cb Nicholls 2004.
| Methods | Retrospective cohort study of an outbreak of influenza A(H3N2) between 10 March and 5 April 2002 in a semi‐closed, highly vaccinated religious community in the UK. 90% of members of the community had been vaccinated before 7 November 2001. Data collected by self completion questionnaire, response rate was 92% (350/380). | |
| Participants | 350 residents of religious community including 133 children aged 0 to 14 years | |
| Interventions | Inactivated trivalent influenza vaccine containing A/Moscow/10/99‐like (H3N2), A/New Caledonia/20/99‐like (H1N1), and B/Sichuan/379/99‐like. The study reports a comparison of efficacy of the vaccine in members vaccinated in the USA with those vaccinated in the UK, in effect testing the hypothesis of possible lower efficacy of the UK‐administered vaccine. | |
| Outcomes |
Serological
Throat swabs from 39 case volunteers, 10 non‐cases, and 5 of undefined status. Paired sera from 9 members and single sera from 2 were drawn. 27 throat swabs were positive for H3N2/Panama/2007/99‐like, which is well matched to vaccine content. Effectiveness A case was defined as self reported fever or chills accompanied by 1 or more of cough, sore throat, headache. Outcomes were evaluated by questionnaires distributed on 2 April 2002. Safety N/A |
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| Funding Source | Unclear | |
| Notes | The authors conclude that the vaccine was not effective in preventing the outbreak, despite being well matched to the circulating virus (risk of developing ILI symptoms was not significantly different between vaccinated and UV: OR 1.14, 95% CI 0.41 to 3.14). VE was ‐5% in those vaccinated in the UK and 77% (53.2% to 88.4%) for those vaccinated elsewhere, mainly in the USA. The study reflects its mostly retrospective nature. The outbreak peaked on 20 March, 5 days before the arrival of the investigators. We do not understand why there is no matching of ILI cases with positive influenza diagnosis by vaccine exposure. Why report effectiveness when they could report efficacy? | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| PCS/RCS‐Selection Exposed cohort | High risk | Selected cohort |
| PCS/RCS‐Selection Non Exposed cohort | Unclear risk | Same community |
| PCS/RCS‐Comparability | High risk | Insufficient information |
| PCS/RCS‐Assessment of Oucome | High risk | Self report |
| Summary assessments | High risk | Plausible bias that seriously weakens confidence in the results |