Effectiveness of seasonal influenza vaccine in preventing medically attended influenza infection in England and Wales during the 2010/2011 season: a primary care-based cohort study.

BACKGROUND: Estimates of seasonal influenza vaccine effectiveness (VE) are affected by factors such as the strain of the current circulating influenza virus and characteristics of the host. OBJECTIVE: The objective of this study was to provide VE estimates for the 2010/2011 seasonal trivalent influenza vaccine (TIV) in preventing medically attended influenza in England and Wales for the season 2010/2011. METHODS: A cohort study design was employed using electronic health records extracted from 104 GP practices in the Royal College of General Practitioners (RCGP) primary care sentinel network. Endpoints included influenza-like illness (ILI), lower respiratory tract infection (LTRI) as well as PCR-confirmed influenza from patients swabbed from practices participating in a swabbing scheme. Adjustment was made for age, month, underlying chronic condition, region and number of consultations in the 12 months prior to the study period. In addition to the cohort analysis, a nested test-negative case-control analysis (TNCC) was carried out using the swab-negative results as controls. RESULTS: In the cohort analysis, VE against LRTI was -0·5% [95% CI: (-7·0%, 7·5%)], against ILI was 37·8% [95% CI: (32·3%, 43·0%)] and against PCR-confirmed influenza was 50·0% [95% CI:(25·9%, 65·6%)] for type A and 44·4% [95% CI: (10·1%, 65·6%)] for type B. Using the TNCC design, the type A VE was 56·5% [95% CI: (30·4%, 72·7%)] and for type B was 54·0% [95% CI: (21·0%, 73·3%)]. CONCLUSIONS: This study shows that the 2010/2011 TIV provided moderate protection against the circulating influenza strains for the 2010/2011 season. It also suggests that VE against the less specific diagnosis of ILI can be found, but less specific endpoints such as LRTI are not useful.

Virological self-sampling to monitor influenza antiviral susceptibility in a community cohort.

OBJECTIVE: To perform antiviral susceptibility monitoring of treated individuals in the community during the 2009 influenza A(H1N1) pandemic in England. PATIENTS AND METHODS: Between 200 and 400 patients were enrolled daily through the National Pandemic Flu Service (NPFS) and issued with a self-sampling kit. Initially, only persons aged 16 and over were eligible, but from 12 November (week 45), self-sampling was extended to include school-age children (5 years and older). All samples received were screened for influenza A(H1N1)pdm09 as well as seasonal influenza [A(H1N1), A(H3N2) and influenza B] by a combination of RT-PCR and virus isolation methods. Influenza A(H1N1)pdm09 RT-PCR-positive samples were screened for the oseltamivir resistance-inducing H275Y substitution, and a subset of samples also underwent phenotypic antiviral susceptibility testing by enzyme inhibition assay. RESULTS: We were able to detect virus by RT-PCR in self-taken samples and recovered infectious virus enabling further virological characterization. The majority of influenza A(H1N1)pdm09 RT-PCR-positive NPFS samples (n = 1273) were taken after oseltamivir treatment had begun. No reduction in phenotypic susceptibility to neuraminidase inhibitors was detected, but five cases with minority quasi-species of oseltamivir-resistant virus (an H275Y amino acid substitution in neuraminidase) were detected. CONCLUSIONS: Self-sampling is a useful tool for community surveillance, particularly for the follow-up of drug-treated patients. The virological study of self-taken samples from the NPFS provided a unique opportunity to evaluate the emergence of oseltamivir resistance in treated individuals with mild illness in the community, a target population that may not be captured by traditional sentinel surveillance schemes.

Ten lessons for the next influenza pandemic-an English perspective: a personal reflection based on community surveillance data.

We review experience in England of the swine flu pandemic between May 2009 and April 2010. The surveillance data from the Royal College of General Practitioners Weekly Returns Service and the linked virological data collected in the integrated program with the Health Protection Agency are used as a reference frame to consider issues emerging during the pandemic. Ten lessons are summarized. (1) Delay between illness onset in the first worldwide cases and virological diagnosis restricted opportunities for containment by regional prophylaxis. (2) Pandemic vaccines are unlikely to be available for effective prevention during the first wave of a pandemic. (3) Open, realistic and continuing communication with the public is important. (4) Surveillance programs should be continued through summer as well as winter. (5) Severity of illness should be incorporated in pandemic definition. (6) The reliability of diagnostic tests as used in routine clinical practice calls for further investigation. (7) Evidence from serological studies is not consistent with evidence based on health care requests made by sick persons and is thus of limited value in cost effectiveness studies. (8) Pregnancy is an important risk factor. (9) New strategies for administering vaccines need to be explored. (10) Acceptance by the public and by health professionals of influenza vaccination as the major plank on which the impact of influenza is controlled has still not been achieved.

Effectiveness of trivalent and pandemic influenza vaccines in England and Wales 2008-2010: results from a cohort study in general practice.

Estimation of influenza vaccine effectiveness (VE) is complicated by various degrees of mismatch between circulating and vaccine strains each season. We carried out a cohort study to estimate VE of trivalent (TIV) and pandemic influenza vaccines (PIV) in preventing various respiratory outcomes among general practice (GP) patients in England and Wales between 2008 and 2010. Dates of consultations for influenza-like illness (ILI), acute respiratory tract infection (ARTI), lower respiratory tract infection (LRTI) and nasopharyngeal swabs were obtained from the patient-level electronic records of the 100 practices enrolled in a national GP network. Dates of vaccination with TIV and PIV were also extracted. Confounders including age, time period and consultation frequency were adjusted for through Poisson regression models. In the winter of 2008/9, adjusted VE of TIV in preventing ILI was 22.3% (95% CI 13.5%, 30.2%). During the 2009/10 winter VE for PIV in preventing ILI was 21.0% (5.3%, 34.0%). The VE for PIV in preventing PCR-confirmed influenza A/H1N1 (2009) was 63.7% (-6.1%, 87.6%). TIV during the period of influenza circulation of 2008/9 and PIV in the winter of 2009/10 were effective in preventing GP consultations for ILI. The cohort study design could be used each season to estimate VE; however, residual confounding by indication could still present issues, despite adjustment for propensity to consult.