Prescribing of neuraminidase inhibitors for influenza in UK primary care since the 2009 pandemic

We determined prescribing rates of neuraminidase inhibitors (NIs) for influenza in UK primary care since 2009 in relation to national prescribing guidelines. All NI prescriptions issued during the influenza seasons between October 2010 and May 2013 were extracted from The Health Improvement Network (THIN), a large UK primary-care database. We calculated NI prescribing rates per 100,000 person-weeks (pw) by age group, sex, deprivation level, influenza season and presence of chronic conditions with 95% confidence intervals (CIs), and used negative binomial regression models to determine the independent association between these variables and NI prescribing. NI prescribing was rare. The prescribing rate was 1·7/100,000 pw (95% CI 1·7-1·8) during influenza-active periods, and 0·1/100,000 (95% CI 0·1-0·1) during non-active periods. Prescribing rates were highest in 25- to 44-year-olds in 2010/2011 and in persons aged ⩾85 years in 2011/2012 and 2012/2013. Individuals with chronic conditions had significantly higher prescribing rates than persons without (rate ratio 2·62, 95% CI 2·27-3·03). GPs are more likely to prescribe NIs to high-risk individuals and during influenza active periods, as per national guidelines. We could not assess the proportion of patients with influenza-like illness who were prescribed an NI.

Mortality caused by influenza and respiratory syncytial virus by age group in England and Wales 1999-2010

BACKGROUND

The mortality burden caused by influenza cannot be quantified directly from death certificates because of under-recording; therefore, the estimated number of influenza deaths has to be obtained through statistical modelling.

OBJECTIVE

To estimate the number of deaths caused by influenza and respiratory syncytial virus (RSV) in England and Wales between 1999 and 2010 using a multivariable regression model.

METHODS

Generalised linear models were used to estimate weekly deaths by age group (<15, 15-44, 45-74 and 75+ years) as a function of positive influenza and RSV isolates. Adjustment was made for temperature variation (using weekly means of daily Central England temperature time series), underlying seasonal variation and temporal trends. The parameters from the model were used to predict the number of deaths caused by influenza and RSV across winter seasons.

RESULTS

Between 7000 and 25 000 deaths across all ages were associated with influenza in the winter periods 1999-2009. The mortality burden was the highest among the over 75 age group, among whom 2·5-8·1% of deaths were caused by influenza. The lowest number of influenza deaths was estimated for the winter 2009/2010 when pandemic influenza A/H1N1 (2009) was the predominant circulating strain. RSV accounted for 5000-7500 deaths each winter season.

CONCLUSIONS

The model presented provides a robust and reasonable approach to estimating the number of deaths caused by influenza and RSV by age group at the end of each winter.

Assessment of baseline age-specific antibody prevalence and incidence of infection to novel influenza A/H1N1 2009

OBJECTIVES

The objectives of the H1N1 2009 serological surveillance project were twofold: to document (1) the prevalence of cross-reactive antibodies to H1N1 2009 by age group in the population of England prior to arrival of the pandemic strain virus in the UK and (2) the age-specific incidence of infection by month as the pandemic progressed by measuring increases in the proportion of individuals with antibodies to H1N1 2009 by age.

METHODS

Residual aliquots of samples submitted to 16 microbiology laboratories in eight regions in England in defined age groups in 2008 and stored by the Health Protection Agency serological surveillance programme were used to document age-stratified prevalence of antibodies to H1N1 2009 prior to the arrival of the pandemic in the UK. Functional antibodies to the H1N1 2009 virus were measured by haemagglutination inhibition (HI) and microneutralisation (MN) assays. For timely measurement of monthly incidence of infection with H1N1 2009 between August 2009 and April 2010, the microbiology serum collections were supplemented by collection of residual sera from chemical pathology laboratories in England. Monthly seroincidence samples were tested by HI only, apart from the final sera collected post pandemic in 2010, which were also tested by MN. Incidence during the pandemic was estimated from changes in prevalence between time points and also by a likelihood-based method.

SETTING

Eight regions of England.

PARTICIPANTS

Serum samples from patients accessing health care in England from whom blood samples were taken for unrelated microbiological or chemical pathology testing.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Baseline age-specific prevalence of functional antibodies to the H1NI 2009 virus prior to the arrival of the pandemic; changes in antibody prevalence during the period August 2009 to April 2010.

RESULTS

Pre-existing cross-reactive antibodies to H1N1 2009 were detected in the baseline sera and increased with age, particularly in those born before 1950. The prediction of immunological protection derived from the baseline serological analysis was consistent with the lower clinical attack rates in older age groups. The high levels of susceptibility in children < 15 years, together with their mixing within school, resulted in the highest attack rates in this age group. Serological analysis by region confirms that there were geographical differences in timing of major pandemic waves. London had a big first wave among the 5- to 14-year age group, with the rest of the country reducing the gap after the second wave. Cumulative incidence in London remained higher throughout the pandemic in each age group. By the end of the second wave it is estimated that as many as 70% of school-aged children in London had been infected. Taken together, these observations are consistent with observations from previous pandemics in 1918, 1957 and 1968 - that the major impact of influenza pandemics is on younger age groups, with a pattern of morbidity and mortality distinct from seasonal influenza epidemics.

CONCLUSIONS

Serological analysis of appropriately structured, age-stratified and geographically representative samples can provide an immense amount of information to set in context other measures of pandemic impact in a population, and provide the most accurate measures of population exposure. National scale seroepidemiology studies require cross-agency coordination, multidisciplinary working, and considerable scientific resource.

FUNDING

The National Institute for Health Research Health Technology Assessment programme and the Health Protection Agency.

Effectiveness of seasonal 2010/11 and pandemic influenza A(H1N1)2009 vaccines in preventing influenza infection in the United Kingdom: mid-season analysis 2010/11

This study provides mid-season estimates of the effectiveness of 2010/11 trivalent influenza vaccine and previous vaccination with monovalent influenza A(H1N1)2009 vaccine in preventing confirmed influenza A(H1N1)2009 infection in the United Kingdom in the 2010/11 season. The adjusted vaccine effectiveness was 34% (95% CI: -10 - 60%) if vaccinated only with monovalent vaccine in the 2009/10 season; 46% (95% CI: 7 - 69%) if vaccinated only with trivalent influenza vaccine in the 2010/11 season and 63% (95% CI: 37 - 78%) if vaccinated in both seasons.

Effectiveness of seasonal 2010/11 and pandemic influenza A(H1N1)2009 vaccines in preventing influenza infection in the United Kingdom: mid-season analysis 2010/11

This study provides mid-season estimates of the effectiveness of 2010/11 trivalent influenza vaccine and previous vaccination with monovalent influenza A(H1N1)2009 vaccine in preventing confirmed influenza A(H1N1)2009 infection in the United Kingdom in the 2010/11 season. The adjusted vaccine effectiveness was 34% (95% CI: -10 - 60%) if vaccinated only with monovalent vaccine in the 2009/10 season; 46% (95% CI: 7 - 69%) if vaccinated only with trivalent influenza vaccine in the 2010/11 season and 63% (95% CI: 37 - 78%) if vaccinated in both seasons.

Effectiveness of pandemic and seasonal influenza vaccine in preventing pandemic influenza A(H1N1)2009 infection in England and Scotland 2009-2010

Following the global spread of pandemic influenza A(H1N1)2009, several pandemic vaccines have been rapidly developed. The United Kingdom and many other countries in the northern hemisphere implemented seasonal and pandemic influenza vaccine programmes in October 2009. We present the results of a case–control study to estimate effectiveness of such vaccines in preventing confirmed pandemic influenza infection. Some 5,982 individuals with influenza-like illness seen in general practices between November 2009 and January 2010 were enrolled. Those testing positive on PCR for pandemic influenza were assigned as cases and those testing negative as controls. Vaccine effectiveness was estimated as the relative reduction in odds of confirmed infection between vaccinated and unvaccinated individuals. Fourteen or more days after immunisation with the pandemic vaccine, adjusted vaccine effectiveness (VE) was 72% (95% confidence interval (CI): 21% to 90%). If protection was assumed to start after seven or more days, the adjusted VE was 71% (95% CI: 37% to 87%). Pandemic influenza vaccine was highly effective in preventing confirmed infection with pandemic influenza A(H1N1)2009 from one week after vaccination. No evidence of effectiveness against pandemic influenza A(H1N1)2009 was found for the 2009/10 trivalent seasonal influenza vaccine (adjusted VE of -30% (95% CI: -89% to 11%)).

Effectiveness of pandemic and seasonal influenza vaccine in preventing pandemic influenza A(H1N1)2009 infection in England and Scotland 2009-2010

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Pandemic Influenza A (H1N1) 2009 and mortality in the United Kingdom: risk factors for death, April 2009 to March 2010

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Pandemic Influenza A (H1N1) 2009 and mortality in the United Kingdom: risk factors for death, April 2009 to March 2010

This paper describes the epidemiology of fatal pandemic influenza A(H1N1) cases in the United Kingdom (UK) since April 2009 and in particular risk factors associated with death. A fatal case was defined as a UK resident who died between 27 April 2009 and 12 March 2010, in whom pandemic influenza A(H1N1) infection was confirmed by laboratory or recorded on death certificate. Case fatality ratios (CFR) were calculated using the estimated cumulative number of clinical cases as the denominator. The relative risk of death was estimated by comparing the population mortality rate in each risk group, with those not in a risk group. Across the UK, 440 fatal cases were identified. In England, fatal cases were mainly seen in young adults (median age 43 years, 85% under 65 years), unlike for seasonal influenza. The majority (77%) of cases for whom data were available (n=308) had underlying risk factors for severe disease. The CFR in those aged 65 years or over was nine per 1,000 (range 3 - 26) compared to 0.4 (range 0.2 to 0.9) for those aged six months to 64 years. In the age group between six month and 64 years, the relative risk for fatal illness for those in a risk group was 18. The population attributable fractions in this age group were highest for chronic neurological disease (24%), immunosuppression (16%) and respiratory disease (15%). The results highlight the importance of early targeted effective intervention programmes.

Rubella seroprevalence in pregnant women in North Thames: estimates based on newborn screening samples

Objectives

Routine screening for rubella susceptibility is recommended in the UK so that women found to be susceptible can be offered immunization in the post partum period. We demonstrate the use of newborn dried blood spot samples linked to routine vital statistics datasets to monitor rubella susceptibility in pregnant women and to investigate maternal characteristics as determinants of rubella seronegativity.

Setting

North Thames region of England (including large parts of inner London).

Methods

Maternally acquired rubella IgG antibody levels were measured in 18882 newborn screening blood spot samples. Latent class regression finite mixture models were used to classify samples as seronegative to rubella. Data on maternal country of birth were available through linkage to birth registration data.

Results

An estimated 2.7% (95% CI 2.4%–3.0%) of newly delivered women in North Thames were found to be seronegative. Mothers born abroad, particularly in Sub-Saharan Africa and South Asia, were more likely to be seronegative than UK-born mothers, with adjusted odds ratios of 4.2 (95% CI 3.1–5.6) and 5.0 (3.8–6.5), respectively. Mothers under 20 years were more likely to be seronegative than those aged 30 to 34.

Conclusion

Our findings highlight the need for vaccination to be targeted specifically at migrant women and their families to ensure that they are protected from rubella in pregnancy and its serious consequences.