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Field effectiveness of pandemic and 2009-2010 seasonal vaccines against 2009-2010 A(H1N1) influenza: estimations from surveillance data in France.

Pelat C, Falchi A, Carrat F, Mosnier A, Bonmarin I, Turbelin C, Vaux S, van der Werf S, Cohen JM, Lina B, Blanchon T, Hanslik T - PLoS ONE (2011)

Bottom Line: The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after.The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after.It was significantly lower against ILI.

View Article: PubMed Central - PubMed

Affiliation: UPMC Université Paris 06, UMRS 707, Paris, France. pelat@u707.jussieu.fr

ABSTRACT

Background: In this study, we assess how effective pandemic and trivalent 2009-2010 seasonal vaccines were in preventing influenza-like illness (ILI) during the 2009 A(H1N1) pandemic in France. We also compare vaccine effectiveness against ILI versus laboratory-confirmed pandemic A(H1N1) influenza, and assess the possible bias caused by using non-specific endpoints and observational data.

Methodology and principal findings: We estimated vaccine effectiveness by using the following formula: VE  =  (PPV-PCV)/(PPV(1-PCV)) × 100%, where PPV is the proportion vaccinated in the population and PCV the proportion of vaccinated influenza cases. People were considered vaccinated three weeks after receiving a dose of vaccine. ILI and pandemic A(H1N1) laboratory-confirmed cases were obtained from two surveillance networks of general practitioners. During the epidemic, 99.7% of influenza isolates were pandemic A(H1N1). Pandemic and seasonal vaccine uptakes in the population were obtained from the National Health Insurance database and by telephonic surveys, respectively. Effectiveness estimates were adjusted by age and week. The presence of residual biases was explored by calculating vaccine effectiveness after the influenza period. The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after. It was 86% (56-98) against confirmed influenza. The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after. It was 60% (41-74) against confirmed influenza.

Conclusions: The effectiveness of pandemic vaccines in preventing confirmed pandemic A(H1N1) influenza on the field was high, consistently with published findings. It was significantly lower against ILI. This is unsurprising since not all ILI cases are caused by influenza. Trivalent 2009-2010 seasonal vaccines had a statistically significant effectiveness in preventing ILI and confirmed pandemic influenza, but were not better in preventing confirmed pandemic influenza than in preventing ILI. This lack of difference might be indicative of selection bias.

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Related in: MedlinePlus

Weekly coverage of pandemic and seasonal vaccines in the population throughout the study period.Red curves: vaccine coverage in the 6 month- to 4 year-old age group; Blue: in the 5 to 14 year-old age group; Green: in the 15 to 64 year-old age group; Violet: in the ≥65 year-old age group. Pandemic vaccination targeted different at-risk groups, which were called in turn, according to a calendar established by French public health authorities. The principal steps of this calendar are outlined below the figure. Grey hatched area: epidemic study period for the effectiveness of pandemic vaccines (weeks 46/2009 to 52/2009); Pink area: epidemic study period for seasonal vaccines (weeks 42/2009 to 52/2009); Blue area: post-epidemic study period for pandemic and seasonal vaccines (weeks 05/2010 to 34/2010).
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pone-0019621-g001: Weekly coverage of pandemic and seasonal vaccines in the population throughout the study period.Red curves: vaccine coverage in the 6 month- to 4 year-old age group; Blue: in the 5 to 14 year-old age group; Green: in the 15 to 64 year-old age group; Violet: in the ≥65 year-old age group. Pandemic vaccination targeted different at-risk groups, which were called in turn, according to a calendar established by French public health authorities. The principal steps of this calendar are outlined below the figure. Grey hatched area: epidemic study period for the effectiveness of pandemic vaccines (weeks 46/2009 to 52/2009); Pink area: epidemic study period for seasonal vaccines (weeks 42/2009 to 52/2009); Blue area: post-epidemic study period for pandemic and seasonal vaccines (weeks 05/2010 to 34/2010).

Mentions: In France, pandemic vaccination conformed to a priority list established by public health authorities based on exposure and/or transmission probability, or on risk of complication subsequent to influenza [1]. The priority allocation of pandemic vaccines is shown in Figure 1, along with the evolution of vaccine coverage over time, by broad age categories. Medical and paramedical staffs working in hospitals were first called, on October 20th (week 43). Individuals working with ambulatory patients presenting with influenza or working with patients at high risk of complication for influenza were called on November 2nd (week 45). Risk factors of complication, stated in a High Committee of Public Health advice, on September 7th 2009, were: pregnancy (in particular from the second trimester), obesity, and chronic conditions such as bronco-pulmonary diseases, heart diseases, diabetes and immunosuppression [2]. On November 12th (week 46) all other health care professional were called (880,000), as well as all persons in contact with infants younger than six month-old (1,200,000), child-minders working with children under three year-old (500,000), and every person between six months and 64 years of age with a risk factor (2,815,000). Pregnant women from their second trimester and 6- to 23 month-old children without risk factor were called on November 20th (week 47). High school pupils were called on November 25th (week 48). People over 65 year-old with a risk factor (3,200,000) and children older than 23 month-old (7,700,000) and were called in week 49. Finally, adults over 18 year-old without a risk factor were called in week 53 (39,000,000). In the end, 63,295,000 persons had been called to vaccination centers to receive a pandemic influenza vaccine: all the French population, except infants younger than 6 month-old.


Field effectiveness of pandemic and 2009-2010 seasonal vaccines against 2009-2010 A(H1N1) influenza: estimations from surveillance data in France.

Pelat C, Falchi A, Carrat F, Mosnier A, Bonmarin I, Turbelin C, Vaux S, van der Werf S, Cohen JM, Lina B, Blanchon T, Hanslik T - PLoS ONE (2011)

Weekly coverage of pandemic and seasonal vaccines in the population throughout the study period.Red curves: vaccine coverage in the 6 month- to 4 year-old age group; Blue: in the 5 to 14 year-old age group; Green: in the 15 to 64 year-old age group; Violet: in the ≥65 year-old age group. Pandemic vaccination targeted different at-risk groups, which were called in turn, according to a calendar established by French public health authorities. The principal steps of this calendar are outlined below the figure. Grey hatched area: epidemic study period for the effectiveness of pandemic vaccines (weeks 46/2009 to 52/2009); Pink area: epidemic study period for seasonal vaccines (weeks 42/2009 to 52/2009); Blue area: post-epidemic study period for pandemic and seasonal vaccines (weeks 05/2010 to 34/2010).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3091864&req=5

pone-0019621-g001: Weekly coverage of pandemic and seasonal vaccines in the population throughout the study period.Red curves: vaccine coverage in the 6 month- to 4 year-old age group; Blue: in the 5 to 14 year-old age group; Green: in the 15 to 64 year-old age group; Violet: in the ≥65 year-old age group. Pandemic vaccination targeted different at-risk groups, which were called in turn, according to a calendar established by French public health authorities. The principal steps of this calendar are outlined below the figure. Grey hatched area: epidemic study period for the effectiveness of pandemic vaccines (weeks 46/2009 to 52/2009); Pink area: epidemic study period for seasonal vaccines (weeks 42/2009 to 52/2009); Blue area: post-epidemic study period for pandemic and seasonal vaccines (weeks 05/2010 to 34/2010).
Mentions: In France, pandemic vaccination conformed to a priority list established by public health authorities based on exposure and/or transmission probability, or on risk of complication subsequent to influenza [1]. The priority allocation of pandemic vaccines is shown in Figure 1, along with the evolution of vaccine coverage over time, by broad age categories. Medical and paramedical staffs working in hospitals were first called, on October 20th (week 43). Individuals working with ambulatory patients presenting with influenza or working with patients at high risk of complication for influenza were called on November 2nd (week 45). Risk factors of complication, stated in a High Committee of Public Health advice, on September 7th 2009, were: pregnancy (in particular from the second trimester), obesity, and chronic conditions such as bronco-pulmonary diseases, heart diseases, diabetes and immunosuppression [2]. On November 12th (week 46) all other health care professional were called (880,000), as well as all persons in contact with infants younger than six month-old (1,200,000), child-minders working with children under three year-old (500,000), and every person between six months and 64 years of age with a risk factor (2,815,000). Pregnant women from their second trimester and 6- to 23 month-old children without risk factor were called on November 20th (week 47). High school pupils were called on November 25th (week 48). People over 65 year-old with a risk factor (3,200,000) and children older than 23 month-old (7,700,000) and were called in week 49. Finally, adults over 18 year-old without a risk factor were called in week 53 (39,000,000). In the end, 63,295,000 persons had been called to vaccination centers to receive a pandemic influenza vaccine: all the French population, except infants younger than 6 month-old.

Bottom Line: The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after.The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after.It was significantly lower against ILI.

View Article: PubMed Central - PubMed

Affiliation: UPMC Université Paris 06, UMRS 707, Paris, France. pelat@u707.jussieu.fr

ABSTRACT

Background: In this study, we assess how effective pandemic and trivalent 2009-2010 seasonal vaccines were in preventing influenza-like illness (ILI) during the 2009 A(H1N1) pandemic in France. We also compare vaccine effectiveness against ILI versus laboratory-confirmed pandemic A(H1N1) influenza, and assess the possible bias caused by using non-specific endpoints and observational data.

Methodology and principal findings: We estimated vaccine effectiveness by using the following formula: VE  =  (PPV-PCV)/(PPV(1-PCV)) × 100%, where PPV is the proportion vaccinated in the population and PCV the proportion of vaccinated influenza cases. People were considered vaccinated three weeks after receiving a dose of vaccine. ILI and pandemic A(H1N1) laboratory-confirmed cases were obtained from two surveillance networks of general practitioners. During the epidemic, 99.7% of influenza isolates were pandemic A(H1N1). Pandemic and seasonal vaccine uptakes in the population were obtained from the National Health Insurance database and by telephonic surveys, respectively. Effectiveness estimates were adjusted by age and week. The presence of residual biases was explored by calculating vaccine effectiveness after the influenza period. The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after. It was 86% (56-98) against confirmed influenza. The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after. It was 60% (41-74) against confirmed influenza.

Conclusions: The effectiveness of pandemic vaccines in preventing confirmed pandemic A(H1N1) influenza on the field was high, consistently with published findings. It was significantly lower against ILI. This is unsurprising since not all ILI cases are caused by influenza. Trivalent 2009-2010 seasonal vaccines had a statistically significant effectiveness in preventing ILI and confirmed pandemic influenza, but were not better in preventing confirmed pandemic influenza than in preventing ILI. This lack of difference might be indicative of selection bias.

Show MeSH
Related in: MedlinePlus