Table 2

Vaccination effects in healthcare workers (the occupational health perspective)

Review IDPopulationLaboratory-confirmed influenzaClinically suspected influenzaSR authors’ conclusions
No. of studies (participants)Efficacy (95% CI)No. of studies (participants)Efficacy (95% CI)On efficacyFor policy
Ng and Lai12HCW1 RCT (359)88% (59 to 96)2 RCTs (606)No significant effect in either study‘No definitive conclusion on the effectiveness of influenza vaccinations in HCWs’‘Further research is necessary to evaluate whether annual vaccination is a key measure to protect HCWs’
Burls et al13HCW1 RCT (361)88% (47 to 97) Inf. A
89% (14 to 99) Inf. B
2 RCTs (606)No significant effect in either study‘Vaccination was highly effective’‘Effective implementation should be a priority’*
Michiels et al14HCW1 non-RCT (262)90% (25 to 99)1 RCT (346)53% (NS) p=0.002None statedNone stated
Demicheli et al19Healthy adults22 RCTs (51 724)62% (56 to 67)16 (25 795)17% (13 to 22)‘Influenza vaccines have a very modest effect in reducing influenza symptoms’‘Results seem to discourage the usage of vaccination against influenza in healthy adults as a routine public health measure.’†
DiazGranados et al15Healthy adultsNot stated59% (50 to 66)‘Influenza vaccines are efficacious’None stated
Osterholm et al17Healthy adults6 (31 892)59% (51 to 67)‘Influenza vaccines provide moderate protection against confirmed influenza’None stated
Villari et al18Healthy adults25 (18 920)63% (53 to 71)49 (46 022)22% (16 to 28)‘Estimates (of effect) vary substantially’‘Further trials…are needed to provide definitive answers for policymakers’
Michiels et al14Healthy adults14 (21 616)44% to 73% (range)19 (19 046)No significant effect‘Inactivated influenza vaccine shows efficacy in healthy adults’None stated
Ferroni and Jefferson16Healthy adults5 (43 830)44% to 77% (range)18 (19 046)7% to 30% (range)‘Inactivated vaccines are effective at reducing infection’None stated
  • *This conclusion may be influenced by the reported effects on protecting patients and days off work in tables 3 and 4, respectively.13

  • †This conclusion is influenced by the additional findings of no demonstrable effect on complications such as pneumonia or transmission.19

  • HCW, healthcare worker; RCTs, randomised controlled trials; SR, systematic review.