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Infectious diseases
Original research
Evaluation of BBIBP-CorV Sinopharm COVID-19 vaccine effectiveness in Sri Lanka: a test-negative case control study
  1. Shamila Thivanshi De Silva1,2,
  2. Dileepa Senajith Ediriweera3,
  3. Wathsala Wimalasena4,
  4. Manjula Kariyawasam5,
  5. Gihan Kosinna4,
  6. Gayan Bogoda4,
  7. Sumudu Senaratne4,
  8. Kanchana Rathnayake4,
  9. Inosha Weerarathna4,
  10. Ranjan Premaratna1,2,
  11. Prasanna Gunasena4
  1. 1Faculty of Medicine, University of Kelaniya, Kelaniya, Sri Lanka
  2. 2Colombo North Teaching Hospital, Ragama, Sri Lanka
  3. 3Centre for Health Informatics, Biostatistics and Epidemiology, University of Kelaniya Faculty of Medicine, Ragama, Sri Lanka
  4. 4State Pharmaceuticals Corporation of Sri Lanka, Colombo, Sri Lanka
  5. 5Epidemiology Unit, Ministry of Health, Sri Lanka, Colombo, Sri Lanka
  1. Correspondence to Professor Shamila Thivanshi De Silva; shamiladp{at}kln.ac.lk

Abstract

Objectives There is limited research on real-world effectiveness of BBIBP-CorV Sinopharm COVID-19 vaccine. This study evaluated real-world effectiveness of Sinopharm vaccine in Sri Lanka by assessing absolute vaccine efficacy.

Design and setting A retrospective test-negative case-control study was conducted at ten large government hospitals across the country.

Participants Consecutive adults aged ≥18 years attending outpatient departments who tested reverse-transcription-PCR positive for SARS-CoV-2 during the study period were recruited.

Main outcome measures An interviewer-administered questionnaire was administered, and outcome of COVID-19 infection was assessed in cases.

Results Of 1829 recruited, 914 (49.9%) were male, and mean age was 45.2 (SD 15.3) years; 1634 (89.3%) were vaccinated with two doses of BBIBP-CorV Sinopharm vaccine, while 195 (10.1%) were vaccine-naïve. Compared with the vaccinated, unvaccinated persons were older but otherwise similar in their demographic and medical profiles. Unvaccinated were more likely to have fever, shortness of breath and vomiting as symptoms and were more likely to seek treatment. Significantly more vaccinated individuals received treatment at home. After admission, the unvaccinated were more likely to receive oxygen. Significantly more unvaccinated persons died of COVID-19 compared with the vaccinated. Sinopharm vaccine was 78.2% (94% CI 69.0% to 85.0%) effective at preventing COVID-19 infection, 88.7% (81.6%–93.2%) effective at preventing severe infection and 85.6% (69.6%–93.6%) effective at preventing death.

Conclusions BBIBP-CorV Sinopharm vaccine is effective at mitigating severity of illness and reducing the likelihood of hospitalisation, severe illness and death, in those who received primary vaccination, compared with the unvaccinated.

  • COVID-19
  • Vaccination
  • PUBLIC HEALTH

Data availability statement

Data are available upon reasonable request. The datasets used and analysed during the current study are available from the corresponding author upon reasonable request. This includes deidentified participant data and related documents (eg: study protocol, statistical analysis). Data will be available with publication from the corresponding author via email with a signed data access agreement.

http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjopen-2024-090341

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    STRENGTHS AND LIMITATIONS OF THIS STUDY

    • Study conducted island-wide with a representative sample of persons.

    • Absolute vaccine efficacy measured since controls were unvaccinated.

    • Test-negative case control study design is an established method for checking vaccine efficacy.

    • Recall bias was unavoidable regarding symptoms of COVID-19.

    • Since this was an observational study, there may be unmeasured confounding variables, although a strong attempt was made to control for known confounders.

    Introduction

    COVID-19 is a global pandemic caused by the SARS-CoV-2. Pneumonia caused by a novel coronavirus initially detected in Wuhan in Hubei province, China was reported to the WHO in December 2019. Unlike other coronaviruses, SARS-CoV-2 spread rapidly all over the world within a short period.1

    The first confirmed case of COVID-19 in Sri Lanka was reported in March 2020. There were 672 054 confirmed cases and 16 832 deaths attributed to COVID-19 reported in the country up to March 2023.2 Initially Alpha (V1) was the dominant variant in Sri Lanka. By mid-2021, the Delta variant was being increasingly detected. In early 2022, Omicron variants B.A.1 and B.A.2 were the dominant variants in the community.3 The vaccination programme against COVID-19 in Sri Lanka commenced in January 2021, when front-line healthcare workers were given the AstraZeneca vaccine.4 Currently, seven vaccines are approved for use in Sri Lanka, namely Pfizer/BioNTech, Oxford AstraZeneca (two formulations), Sinopharm, Moderna, Sinovac and Sputnik V. BBIBP-CorV Sinopharm is the most used vaccine, accounting for approximately 60% of all vaccine doses administered.4 5 As of March 2023, 40 116 590 vaccine doses have been administered, with 17 143 761 persons (77.3% of the population) vaccinated with at least one dose and 14 752 827 persons (66.6% of the population) fully vaccinated in Sri Lanka.6 In a lower middle-income country with a total population of 22.16 million in 2021,7 this amounts to an impressive 187.34 total doses administered per 100 population.

    SARS COV-2 has imposed an enormous global burden by developing new variants with fluctuating disease severity and mortality throughout the pandemic.8 Immunisation is one of the most effective methods to control this global pandemic.9 Therefore, effectiveness of vaccines and their safety in the real world compared with clinical trials is an essential area of study. Many studies have investigated the vaccine effectiveness (VE) of Pfizer, Moderna, and Oxford AstraZeneca vaccines. There is limited research on real-world effectiveness of the BBIBP-CorV Sinopharm vaccine.

    This study aimed to determine the effectiveness of BBIBP-CorV Sinopharm vaccine at preventing primary infections with COVID-19 and the outcome after infection in those who did and did not receive the vaccine.

    Methods

    A test-negative case-control study was conducted at 10 government hospitals in Sri Lanka, with one major hospital selected from each of the nine provinces in the country during a 7-month period (December 2021 to June 2022).

    All consenting, consecutive persons aged 18 years or more who visited the outpatient department of the selected government hospitals during the study period to test their reverse-transcription-PCR (rRT-PCR) for SARS-CoV-2 were included in the study. Persons who had received only one dose of the BBIBP-CorV Sinopharm vaccine, those who had received two doses of the BBIBP-CorV Sinopharm vaccine but were within 14 days of the second dose and those who had received at least one dose of a vaccine other than BBIBP-CorV Sinopharm were excluded from the study. The WHO sample size calculator for VE was used to determine the sample size assuming 50% predicted VE, 10% desired precision and 50% coverage among controls.10

    A list of attendees who visited the outpatient department to check rRT-PCR for SARS-CoV-2 status was obtained from each hospital. All consecutive persons aged 18 years and above were short-listed. RT-PCR-positive persons from the short-listed were selected as cases, and RT-PCR-negative persons were selected as controls. Names, contact details and addresses of selected persons were obtained from the hospital records, with the permission of hospital directors.

    An interviewer-administered questionnaire was administered by telephone by trained research assistants (online supplemental file 1). Informed verbal consent was obtained once inclusion and exclusion criteria were verified. If a candidate met exclusion criteria, then the next hospital attendee in the RT-PCR list was considered according to his/her test result. The brief questionnaire contained demographic data, COVID-19 vaccination details, medical history and details of the current illness. Vaccination status was verified by checking vaccination cards sent to the investigators via messenger apps. Vaccination status of all participants was also cross-checked with the Ministry of Health of Sri Lanka Epidemiology Unit Vaccination Database using the National Identity Card number. All data were directly entered into a centralised system (REDCap) maintained at the Faculty of Medicine, University of Kelaniya.

    Outcome was verified in cases (severity of infection, hospital stay, intensive care unit (ICU) admission and death). Participants were asked to send a photograph of their diagnosis card to a designated phone number. When a participant had severe disease and was in hospital, the next of kin was contacted to obtain details about the participant’s status. Consent of the next of kin was obtained prior to requesting any data of hospitalised patients. If a participant had died, details were obtained from the next of kin with his/her consent, and the death certificate was obtained via a messenger app for verification.

    Disease was classified as asymptomatic, mild, moderate, severe and critical using standard criteria:11

    • Asymptomatic or presymptomatic infection: individuals who test positive for SARS-CoV-2 using a virologic test but have no symptoms consistent with COVID-19.

    • Mild illness: individuals who have any of the various signs and symptoms of COVID-19 but do not have shortness of breath, dyspnoea, or abnormal chest imaging.

    • Moderate illness: individuals who show evidence of lower respiratory disease during clinical assessment or imaging and who have an oxygen saturation measured by pulse oximetry (SpO2) ≥94% on room air at sea level.

    • Severe illness: individuals who have SpO2 <94% on room air at sea level, a ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/Fio2) <300 mm Hg, a respiratory rate >30 breaths per minute or lung infiltrates >50%.

    • Critical illness: individuals who have respiratory failure, septic shock, and/or multiple organ dysfunction.

    Descriptive data analysis was done to present study population characteristics. Means, SD, median and quartiles were reported for continuous variables, and numbers with percentages were reported for categorical data. Independent sample t-test was used to assess the group difference for the continuous variables, and χ2 test and or Fisher’s exact test was used to assess the group difference for categorical variables (online supplemental file 2).

    Logistic regression models were used to assess the effectiveness of the Sinopharm vaccine against SARS-CoV-2 infection, moderate-to-severe COVID-19 and deaths. This was done by estimating the OR of events of interest among vaccinated compared with those who were not vaccinated. Multiple logistic regression models were used to obtain the adjusted ORs.12 The ORs of breakthrough cases were adjusted for age, gender and exposure to COVID-19, while ORs of severe COVID-19 cases and deaths were adjusted for age, sex and presence of comorbidities.

    Embedded Image

    One minus the OR of vaccination is considered the direct VE:

    VE = (1 – OR)*100%.

    VE measured is absolute VE and is of the primary series (unboosted VE), since study subjects received the primary series vaccination only and had not received booster or third doses at the time of recruitment.

    The model for moderate-to-severe COVID-19 showed significant interactions between vaccination status and age, as well as vaccination status and the presence of comorbidities. Exploratory analysis showed age >45 as the cut-off age that resulted in a difference in VE. Therefore, VE was separately evaluated for those less than or equal to 45 years and more than 45 years of age, as well as the presence and absence of comorbidities. The interaction between vaccination status and the presence of comorbidities was not significant when the vaccination status and the age interaction were considered in the model, indicating a potential confounding effect between age and comorbidities. In this study, we present the results of both interactions considering their clinical importance.

    For the sensitivity analysis, we employed two methods to assess the robustness of our results. First, we obtained adjusted VE estimates by controlling for age, sex, exposure to COVID-19 and the presence of comorbidities. Second, we analysed 1000 bootstrap samples, each comprising 75% of the original data with replacement. This approach allowed us to evaluate the variability and stability of our findings under different sampling scenarios. Statistical analysis was done with Top of FormR programming language V.4.0.0.

    Patient and public involvement

    Patients were first involved in this research when they were recruited to the pilot study. Research questions and outcome measures were influenced by patient responses to the pilot study. Information obtained in the pilot study was not used in the final analysis.

    There was no direct public or patient involvement in the design, recruitment and conduct of the study. Patients were informed about the time required to participate in the research prior to recruitment. The public will be directly involved in the dissemination of study results, since these results are likely to influence public perception regarding vaccination.

    Results

    A total of 1829 persons fulfilling inclusion criteria were recruited; 914 (49.97%) were males, and mean age was 45.2 (SD 15.3) years. Nine hundred and four people (49.43%) tested positive on COVID-19 PCR. Most (1634 (89.3%)) were vaccinated with two doses of BBIBP-CorV Sinopharm vaccine, while 195 (10.1%) were vaccine-naïve (table 1).

    View this table:
    Table 1

    COVID status versus vaccination status of the sample

    The unvaccinated had higher incidence of COVID-19 infections than the vaccinated (79.5% vs 45.8%, p<0.001). Among those who developed COVID-19 infection, the unvaccinated were older than those vaccinated (49 vs 45, p<0.05). The unvaccinated had significantly more symptoms of fever, chills, myalgia and arthralgia, headache, shortness of breath, runny nose and nasal congestion, sore throat and vomiting (table 2). Asymptomatic persons presented for testing mainly after close contact with a COVID-19 infected (or strongly suspected to be infected) person.

    View this table:
    Table 2

    Demographic and symptom comparison between vaccinated and unvaccinated in those who developed COVID-19 infection

    Of 904 participants who developed COVID-19 infection, 72% sought treatment, with a higher percentage of non-vaccinated individuals seeking treatment than vaccinated individuals (95% vs 67%, p<0.001). The treatment setting also varied significantly (p<0.001): 63% of participants were treated at home (14% non-vaccinated vs 74% vaccinated), 31% in hospital wards (81% non-vaccinated vs 21% vaccinated), 3.4% in intermediate care centre (ICC) wards (1.3% non-vaccinated vs 3.9% vaccinated) and 1.7% in the intensive care units (3.2% non-vaccinated vs 1.3% vaccinated). Oxygen therapy was administered to 8% of participants, with a higher proportion among non-vaccinated individuals than vaccinated individuals (26% vs 4.3%, p<0.001) requiring oxygen. Mortality rates showed differences, with 10% of non-vaccinated participants succumbing to the disease compared with 1.6% of vaccinated participants (p<0.001) (table 3).

    View this table:
    Table 3

    Outcome of COVID-19 infection in vaccinated versus unvaccinated persons

    Vaccine effectiveness

    The unadjusted OR for contracting COVID-19 among vaccinated individuals compared with unvaccinated individuals was 0.218 (95% CI 0.150 to 0.310), indicating a VE of 78.2% (95% CI 69.0% to 85.0%). After adjusting for age, gender and exposure, the adjusted OR was 0.204 (95% CI 0.134 to 0.308), with an adjusted VE of 79.6% (95% CI 69.2% to 86.6%). Among the infected participants, severe COVID-19 was observed in 28.4% (44/155) of unvaccinated individuals and 4.2% (32/749) of vaccinated individuals, resulting in an unadjusted OR of 0.113 (95% CI 0.068 to 0.184) and VE of 88.7% (95% CI 81.6% to 93.2%).

    For those aged ≤45 years, 20.8% (15/72) of unvaccinated and 0.2% (1/443) of vaccinated individuals developed severe COVID-19, with an adjusted OR of 0.008 (95% CI 0.0004 to 0.04) and an effectiveness of 99.2% (95% CI 95.9% to 99.6%). For those aged >45 years, 34.9% (29/83) of unvaccinated and 10.1% (31/306) of vaccinated individuals developed severe COVID-19, yielding an adjusted OR of 0.20 (95% CI 0.11 to 0.36) and an effectiveness of 80.2% (95% CI 63.8% to 89.3%).

    For those without comorbidities, 19.8% (16/81) of unvaccinated and 0.6% (3/463) of vaccinated individuals developed severe COVID-19, with an unadjusted OR of 0.03 (95% CI 0.01 to 0.09) and VE of 97.2% (95% CI 91.3% to 99.4%). For those with comorbidities, 37.8% (28/74) of unvaccinated and 10.1% (29/286) of vaccinated individuals developed severe COVID-19, resulting in an unadjusted OR of 0.18 (95% CI 0.09 to 0.34) and a VE of 82.5% (95% CI 66.4% to 91.0%).

    Among the 904 infected participants, 10.3% (16/155) of unvaccinated and 1.6% (12/749) of vaccinated individuals died due to COVID-19. The unadjusted OR was 0.141 (95% CI 0.064 to 0.304), indicating an effectiveness of 85.6% (95% CI 69.6% to 93.6%). After adjusting for age, gender and comorbidities, the adjusted OR was 0.19 (95% CI 0.08 to 0.043), with an adjusted effectiveness of 81.2% (95% CI 57.0% to 92.0%) (table 4).

    View this table:
    Table 4

    Effectiveness of the Sinopharm vaccine against SARS-CoV-2 infection, moderate-to-severe COVID-19 and death

    Sensitivity analysis

    The bootstrap analysis yielded a mean unadjusted VE for contracting COVID-19 infection of 77.8% (95% CI 68.8% to 85.7%) and an adjusted VE of 77.7% (95% CI 67.1% to 86.0%) across the 1000 samples, indicating consistency with the primary results. The mean unadjusted VE for severe COVID-19 was 88.2% (95% CI 78.9% to 94.0%); adjusted VE was 99.2% (95% CI 96.4% to 100.0%) for individuals aged equal or less than 45 years, and 79.0% (95% CI 59.7% to 90.8%) for individuals over 45 years; adjusted VE was 97.1% (95% CI 90.7% to 100.0%) for individuals without comorbidities, and 82.0% (95% CI 61.8% to 92.4%) for individuals with comorbidities across the 1000 samples, reflecting alignment with the initial findings. The mean unadjusted VE for deaths was 84.2% (95% CI 62.4% to 95.0%) and an adjusted VE of 79.7% (95% CI 49.2% to 94.4%) across the 1000 samples, confirming consistency with the original results.

    Discussion

    This test-negative case-control study investigated the vaccine efficacy of BBIBP-CorV Sinopharm COVID-19 in a representative sample of 1829 individuals from all over Sri Lanka. The results of the study showed that the vaccine was 78.2% effective at preventing infection with COVID-19, 88.7% effective at preventing severe infection and 85.6% effective at preventing death due to COVID-19 infection in the population studied.

    These findings are comparable with similar studies of BBIBP-CorV Sinopharm COVID-19 vaccine conducted in other countries, indicating that the vaccine is effective at preventing COVID-19 infection and its severe outcomes across different populations. A study from the United Arab Emirates13 found that those who were partially immunised with Sinopharm vaccine were 62% less likely to be hospitalised and those who were fully immunised were 95% less likely to be hospitalised compared with the unvaccinated. A study from Argentina on 237 330 individuals older than 60 years found that the BBIBP-CorV Sinopharm vaccine showed effectiveness in reducing infection and death by SARS-CoV-2 and COVID-19, with 85% effectiveness in reducing death.14 Another study of over 3 million individuals in UAE showed that the BBIBP-CorV Sinopharm vaccine was 79.6% effective against hospitalisation, 86% against critical care admission and 84.1% against death due to COVID-19.15 Wang et al in a summary on efficacy of the BBIBP-CorV Sinopharm vaccine commented that compared with messenger RNA vaccines, BBIBP-CorV seems to show less immunogenicity and durability on laboratory testing, but its real-world effectiveness in preventing severe diseases appears valuable.16

    It is important to note that these studies vary in terms of the size of the study population, the age and health status of the participants, and the timing of the study. Additionally, the studies were conducted in different countries with different COVID-19 variants circulating, which could impact the effectiveness of the vaccine. Overall, the BBIBP-CorV Sinopharm vaccine has been shown to have a high efficacy rate against COVID-19 infection in multiple studies, although the exact efficacy rate varies depending on the study.

    The real-world effectiveness of the Pfizer/BioNTech, Oxford AstraZeneca and Moderna vaccines have been extensively studied in multiple studies. A study carried out in the USA in 2021 shows 82% and 94% effectiveness of single-dose and complete two-dose regimes of both Pfizer-BioNTech and Moderna COVID-19 vaccines, respectively.17 A test-negative case-control study carried out in the UK in 2021 showed that adjusted VE of single-dose Pfizer was 71.4%, and single-dose Oxford–AstraZeneca was 80.4%. The study concluded that immunisation was effective in reducing COVID-19 related hospitalisation in the elderly.18 A 95.3% of adjusted estimated VE was noted 7 days or more after the second dose of Pfizer vaccine in an observational study from Israel in 2021. The Pfizer vaccine was effective in reducing symptomatic disease, hospitalisation, severe disease and death caused by B.1.1.7 SARS-CoV-2 variant in all recommended age groups.19 A retrospective analysis done in 2020–2021 in the Mayo Clinic health system showed that Pfizer and Moderna vaccines provided 86.1% and 93.3% real-world VE at preventing SARS-CoV-2 infection, respectively. The study also revealed 100% effectiveness of both vaccines in preventing ICU admissions.20

    In the current study, compared with the vaccinated, the unvaccinated were older but were otherwise similar in their demographic and medical profiles. This suggests that vaccination status may not be related to underlying health conditions or demographic factors but rather a personal choice. Unvaccinated individuals had a higher incidence of COVID-19 infection compared with vaccinated individuals (79% vs 46%, p<0.001), which is consistent with previous studies.21–24 Also, unvaccinated individuals who developed COVID-19 infection were older than vaccinated individuals who developed the infection. This may be due to older individuals being more hesitant to get vaccinated or having more barriers to access vaccines.

    The study also found that unvaccinated individuals who contracted COVID-19 had more symptoms compared with vaccinated individuals, including fever, chills, myalgia and arthralgia, headache, shortness of breath, runny nose and nasal congestion, sore throat and vomiting. This highlights the importance of vaccination in reducing the severity of COVID-19 symptoms, a feature previously observed in other vaccine efficacy studies.13 25 The unvaccinated were more likely to seek treatment, probably because of being more symptomatic. Significantly more vaccinated individuals received treatment at home, which was presumably due to reduced severity of symptoms.

    The main strength of this study was that it was conducted island-wide with a representative sample of persons. VE measured is absolute VE since controls were unvaccinated, which is another strength of the study. The study design used is an established method for checking VE. However, the sample size was relatively small, and the potential impact of new variants of COVID-19 on vaccine efficacy was not analysed in detail. There was no physical contact with participants, since all information was obtained via telephone interviews. Recall bias was unavoidable regarding symptoms of COVID-19. There were several non-responders as well.

    Since this was an observational study, there may be unmeasured confounding variables, although a strong attempt was made to control for known confounders. Information on the time between completion of the primary series and entry to the study was also not available.

    The choice of a test-negative case-control study design for evaluating VE is well-suited to minimising confounding factors such as healthcare-seeking behaviour. However, the design inherently carries potential biases that warrant consideration. Specifically, recall bias and misclassification of exposure or outcome are potential limitations. Despite the strengths of our study, such potential biases must be acknowledged. Although recall bias is mitigated by the stringent verification of vaccination status through documented records and cross-referencing with official databases, the possibility of residual bias remains. Misclassification of exposure is minimised by using validated vaccination records, but some inaccuracies may still exist. Similarly, while rRT-PCR is highly reliable, potential misclassification of COVID-19 outcomes cannot be entirely ruled out. These biases could influence our study’s conclusions, potentially leading to either an overestimation or underestimation of VE.

    Conclusions

    The BBIBP-CorV Sinopharm vaccine was effective in reducing the incidence of COVID-19 infection and preventing severe illness and death. The findings of the current study are consistent with previous research that has shown that BBIBP-CorV Sinopharm vaccination reduces the risk of COVID-19 infection and severity of the disease. The Top of Form study highlights the importance of vaccination in reducing the incidence of COVID-19 infection and severity of the disease. Vaccination should be encouraged, particularly among older individuals and those with underlying health conditions. Further research is needed to explore the long-term efficacy and safety of COVID-19 vaccines and the potential impact of new variants of the virus on vaccine efficacy.

    Data availability statement

    Data are available upon reasonable request. The datasets used and analysed during the current study are available from the corresponding author upon reasonable request. This includes deidentified participant data and related documents (eg: study protocol, statistical analysis). Data will be available with publication from the corresponding author via email with a signed data access agreement.

    Ethics statements

    Patient consent for publication

    Ethics approval

    This study involves human participants and was approved by Ethics Review Committee, Faculty of Medicine, University of Kelaniya (Approval No – P/133/09/2021). Participants gave informed consent to participate in the study before taking part.

    Acknowledgments

    We gratefully acknowledge the assistance given by the Director General Health Services, all hospital directors, doctors, nurses and other staff of the outpatient departments of the hospitals who supported us in conducting this study. We especially thank the participants of the study for their cooperation.

    References

    1. ↵
      1. Ge H,
      2. Wang X,
      3. Yuan X, et al
      . The epidemiology and clinical information about COVID-19. Eur J Clin Microbiol Infect Dis 2020;39:1011–9. doi:10.1007/s10096-020-03874-z
      OpenUrlCrossRefPubMed
    2. ↵
      WHO global COVID-19 tracker country situation Sri Lanka. Available: https://covid19.who.int/region/searo/country/lk [Accessed 26 Mar 2023].
    3. ↵
    4. ↵
      1. Epidemiology Unit
      . COVID-19 national epidemiological report. Available: https://www.epid.gov.lk/web/index.php?option=com_content&view=article&id=231&Itemid=487&lang=en [Accessed 26 Mar 2023].
    5. ↵
      1. Epidemiology Unit
      . COVID-19 vaccination summary. Available: https://www.epid.gov.lk//storage/post/pdfs/covid_vaccination_2022-10_30.pdf [Accessed 26 Mar 2023].
    6. ↵
      Sri Lanka – COVID19 vaccine tracker. Available: https://covid19.trackvaccines.org/country/sri-lanka/ [Accessed 20 Aug 2021].
    7. ↵
      The world bank population total - Sri Lanka. Available: https://data.worldbank.org/indicator/SP.POP.TOTL?locations=LK [Accessed 26 Mar 2023].
    8. ↵
      1. Moore JP,
      2. Offit PA
      . SARS-CoV-2 Vaccines and the Growing Threat of Viral Variants. JAMA 2021;325:821–2. doi:10.1001/jama.2021.1114
      OpenUrl
    9. ↵
      1. Gebru AA,
      2. Birhanu T,
      3. Wendimu E, et al
      . Global burden of COVID-19: Situational analyis and review. Hum Antibodies 2021;29:139–48. doi:10.3233/HAB-200420
      OpenUrlCrossRef
    10. ↵
    11. ↵
      1. COVID-19 Treatment Guidelines Panel
      . Coronavirus disease 2019 (COVID-19) treatment guidelines. National Institutes of Health. Available: https://www.covid19treatmentguidelines.nih.gov/ [Accessed 12 Jun 2021].
    12. ↵
      1. Schnitzer ME
      . Estimands and Estimation of COVID-19 Vaccine Effectiveness Under the Test-Negative Design: Connections to Causal Inference. Epidemiology 2022;33:325–33. doi:10.1097/EDE.0000000000001470
      OpenUrlCrossRef
    13. ↵
      1. Mousa M,
      2. Albreiki M,
      3. Alshehhi F, et al
      . Similar effectiveness of the inactivated vaccine BBIBP-CorV (Sinopharm) and the mRNA vaccine BNT162b2 (Pfizer-BioNTech) against COVID-19 related hospitalizations during the Delta outbreak in the UAE. J Travel Med 2022;29:taac036. doi:10.1093/jtm/taac036
    14. ↵
      1. Rearte A,
      2. Castelli JM,
      3. Rearte R, et al
      . Effectiveness of rAd26-rAd5, ChAdOx1 nCoV-19, and BBIBP-CorV vaccines for risk of infection with SARS-CoV-2 and death due to COVID-19 in people older than 60 years in Argentina: a test-negative, case-control, and retrospective longitudinal study. Lancet 2022;399:1254–64. doi:10.1016/S0140-6736(22)00011-3
      OpenUrlCrossRef
    15. ↵
      1. Al Kaabi N,
      2. Oulhaj A,
      3. Ganesan S, et al
      . Effectiveness of BBIBP-CorV vaccine against severe outcomes of COVID-19 in Abu Dhabi, United Arab Emirates. Nat Commun 2022;13:3215. doi:10.1038/s41467-022-30835-1
    16. ↵
      1. Wang C,
      2. Chen L-Y,
      3. Lu Q-B, et al
      . Vaccination with the Inactivated Vaccine (Sinopharm BBIBP-CorV) Ensures Protection against SARS-CoV-2 Related Disease. Vaccines (Basel) 2022;10:920. doi:10.3390/vaccines10060920
    17. ↵
      1. Pilishvili T,
      2. Fleming-Dutra KE,
      3. Farrar JL, et al
      . Interim Estimates of Vaccine Effectiveness of Pfizer-BioNTech and Moderna COVID-19 Vaccines Among Health Care Personnel - 33 U.S. Sites, January-March 2021. MMWR Morb Mortal Wkly Rep 2021;70:753–8. doi:10.15585/mmwr.mm7020e2
      OpenUrlCrossRefPubMed
    18. ↵
      1. Glampson B,
      2. Brittain J,
      3. Kaura A, et al
      . Assessing COVID-19 Vaccine Uptake and Effectiveness Through the North West London Vaccination Program: Retrospective Cohort Study. JMIR Public Health Surveill 2021;7:e30010. doi:10.2196/30010
    19. ↵
      1. Haas EJ,
      2. Angulo FJ,
      3. McLaughlin JM, et al
      . Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data. The Lancet 2021;397:1819–29. doi:10.1016/S0140-6736(21)00947-8
      OpenUrl
    20. ↵
      1. Pawlowski C,
      2. Lenehan P,
      3. Puranik A, et al
      . FDA-authorized mRNA COVID-19 vaccines are effective per real-world evidence synthesized across a multi-state health system. Med 2021;2:979–92. doi:10.1016/j.medj.2021.06.007
      OpenUrl
    21. ↵
      1. Hall VJ,
      2. Foulkes S,
      3. Saei A, et al
      . COVID-19 vaccine coverage in health-care workers in England and effectiveness of BNT162b2 mRNA vaccine against infection (SIREN): a prospective, multicentre, cohort study. Lancet 2021;397:1725–35. doi:10.1016/S0140-6736(21)00790-X
      OpenUrlCrossRefPubMed
    22. ↵
      1. Hyams C,
      2. Marlow R,
      3. Maseko Z, et al
      . Effectiveness of BNT162b2 and ChAdOx1 nCoV-19 COVID-19 vaccination at preventing hospitalisations in people aged at least 80 years: a test-negative, case-control study. Lancet Infect Dis 2021;21:1539–48. doi:10.1016/S1473-3099(21)00330-3
      OpenUrl
    23. ↵
      1. Lopez Bernal J,
      2. Andrews N,
      3. Gower C, et al
      . Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study. BMJ 2021;373:n1088. doi:10.1136/bmj.n1088
    24. ↵
      1. Butt AA,
      2. Omer SB,
      3. Yan P, et al
      . SARS-CoV-2 Vaccine Effectiveness in a High-Risk National Population in a Real-World Setting. Ann Intern Med 2021;174:1404–8. doi:10.7326/M21-1577
      OpenUrl
    25. ↵
      1. Tenforde MW,
      2. Olson SM,
      3. Self WH, et al
      . Effectiveness of Pfizer-BioNTech and Moderna Vaccines Against COVID-19 Among Hospitalized Adults Aged ≥65 Years - United States, January-March 2021. MMWR Morb Mortal Wkly Rep 2021;70:674–9. doi:10.15585/mmwr.mm7018e1
      OpenUrlCrossRefPubMed

    Supplementary materials

    Footnotes

    • X @Thivanshi

    • Contributors STDS and DSE conceptualised and designed the study. DSE prepared and established the REDCap data capture system. WW, GK, GB, SS, KR and IW collected data with assistance from RP. MK assisted in verifying data. DSE analysed the data. STDS prepared and revised the manuscript together with DSE, MK, WW and RP. PG was instrumental in securing a grant to conduct the study. All authors read and agreed to the final version of the manuscript. STDS is the guarantor.

    • Funding We gratefully acknowledge a grant from the State Pharmaceutical Corporation of Sri Lanka for the conduct of this study. The funding body played no role in the design of the study and collection, analysis and interpretation of data and in writing the manuscript.

    • Competing interests None declared.

    • Patient and public involvement Patients and/or the public were involved in the design, conduct, reporting or dissemination plans of this research. Refer to the Methods section for further details.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.