Elsevier

Vaccine

Volume 28, Issue 47, 3 November 2010, Pages 7460-7467
Vaccine

Effectiveness of seasonal 2008–2009, 2009–2010 and pandemic vaccines, to prevent influenza hospitalizations during the autumn 2009 influenza pandemic wave in Castellón, Spain. A test-negative, hospital-based, case–control study

https://doi.org/10.1016/j.vaccine.2010.09.042Get rights and content

Abstract

We estimate the impact of the two previous influenza seasonal vaccines and the pandemic vaccine on risk of A (H1N1) 2009 laboratory confirmed hospitalizations during the autumn 2009 pandemic wave in Castellón, Spain. We conducted a test-negative, hospital-based, case–control study. Influenza A (H1N1) 2009 infection was detected in 147 (44%) of 334 patients hospitalized for a presumptive influenza related illness. No effect was observed for the 2008–2009 and 2009–2010 seasonal influenza vaccines. However, the pandemic vaccine was associated with an adjusted vaccine effectiveness of 90% (95% CI, 48–100%). Pandemic vaccines were effective in preventing pandemic influenza associated hospitalizations.

Introduction

In April 2009 a new influenza A virus emerged (A/California/04/2009) [1] that expressed pandemic potential characteristics [2]. By June 2009, World Health Organization declared a Phase 6 pandemic [3]. This situation triggered the deployment of a number of contingency measures, it was decided not to interrupt the manufacture of the influenza trivalent seasonal 2009–2010 vaccine, recommended in February 2009 for the Northern Hemisphere [4] and the process leading to the manufacture, approval and distribution of a vaccine against the new pandemic virus was expedited. Pandemic vaccine formulations, containing the haemagglutinin of the new pandemic strain, adjuvanted and with low antigen content were manufactured in Europe, with the intent to have them available as soon as possible and at least before the second pandemic wave forecasted for early 2009 autumn.

Seasonal 2009–2010 influenza vaccine was offered in Spain, free of charge, to the usual risk groups, beginning 28 September 2009. The influenza virus strains included in this seasonal vaccine were antigenically and genetically distinct from the A (H1N1) 2009 pandemic influenza virus [5]. Beginning 16 November 2010, two adjuvanted, low antigen pandemic vaccines [6], were offered to the same risk groups as traditional influenza vaccines, but age in itself was not considered a risk factor. Due to the observations made during the spring and summer pandemic waves [7], [8], [9], [10], obese persons were included as a group at risk.

Focetria® (7.5 μg haemagglutinin with MF59 as adjuvant, Novartis Vaccines and Diagnostics) was, mainly for logistic reasons, used as recommended in individuals 6 months to 18 years of age and in 60 years old or older. While, Pandemrix® (3.75 μg haemagglutinin with AS03 as adjuvant, GlaxoSmithKline Vaccines) was used in those 18–59 years of age. Pregnant women were offered, beginning 23 November, Panenza® (15 μg of haemagglutinin, Sanofi), a non-adjuvanted full-antigenic-dose pandemic vaccine. The strain included in all these pandemic vaccines was fully matched to the circulating pandemic strain [6].

Meanwhile, the public response to the vaccination with the new pandemic vaccines was one of reluctance, fuelled by the incertitude about the seriousness of the threat caused by the new virus, and of concern, produced by the scarcity of available information on the safety or the effectiveness of those new vaccines [11], [12].

Our goal was to determine the impact of seasonal 2008–2009, 2009–2010 influenza vaccines and the new pandemic influenza vaccine on the risk of hospitalization episodes associated with laboratory-confirmed A (H1N1) 2009 influenza infection.

Section snippets

Study design

We conducted a test-negative case–control study [13] in two health districts, with 482,329 inhabitants, located in the province of Castellón, Spain. The study was part of the epidemiologic surveillance and vaccination program activities deployed in response to the pandemic threat, for this reason it was not submitted for approval to an independent Research Ethics Committee. In all aspects, it was performed according to Good Clinical Practices principles and the Helsinki Declaration (Seoul,

Results

From week 42/2009 the reports of new A (H1N1) 2009 laboratory-confirmed cases escalated until a peak was reached on week 47/2009, thereafter, the number of positive cases diminished till week 2/2010 (Fig. 1), where no cases were reported for two consecutive weeks. During this period, the reference laboratory performed 349 RT-PCR tests in hospitalized patients (Fig. 2), of these, 154 (44.1%) were positive for A (H1N1) 2009, 147 met the inclusion criteria and considered cases and data was

Discussion

The emergence of A (H1N1) 2009 influenza virus coinciding with the end of the Northern Hemisphere influenza season and at the beginning of the Southern Hemisphere influenza season gave ample opportunity to explore the effect of the 2008–2009 Northern Hemisphere influenza season vaccine on the risk of disease for this new emerging virus [24], [25]. The studies published [24], [26], [27], [28], [29], [30], [31] offered results that covered all the possibilities, from the 2008–2009 seasonal

Conclusions

Albeit our results are to be interpreted having all the mentioned limitations and unknowns into account, the autumn 2009 pandemic wave, that took place in Castellón, provided us with the opportunity to try to estimate the impact, on the risk of severe influenza outcomes, of the influenza vaccines used in the previous and present influenza season and the pandemic vaccine administered when the wave was near its peak and to use for that purpose a traditional case–control design [23], with the

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