Abstract
The objective of this study was to identify factors related to the expansion of infection and prevention of influenza A(H1N1)pdm09. A retrospective non-randomized cohort study (from June 2009 to May 2010) on influenza A(H1N1)pdm09 was conducted in a sample of residents from Hiroshima Prefecture, Japan. The cumulative incidence of the influenza A(H1N1)pdm09 and the pandemic vaccine effectiveness (VE) were estimated. The response rate was 53.5% (178,669/333,892). Overall, the odds ratio of non-vaccinated group to vaccinated group for cumulative incidence of influenza A(H1N1)pdm09 was 2.18 (95% confidence interval (CI): 2.13–2.23) and the VE was 43.9% (CI: 42.8–44.9). The expansion of infection, indicating the power of transmission from infected person to susceptible person, was high in the 7–15 years age groups in each area. In conclusion, results from this survey suggested that schoolchildren-based vaccination rate participates in determining the level of herd immunity to influenza and children might be the drivers of influenza transmission. For future pandemic preparedness, vaccination of schoolchildren may help to prevent disease transmission during influenza outbreak.
Highlights
In the 20th century, there were three influenza pandemics: the 1918–1919 Spanish flu (A/H1N1), the 1957–1958 Asian flu (A/H2N2), and the 1968–1969 Hong Kong flu (A/H3N2) [1]
In order to assess the impact of age-specific vaccination program on herd immunity, we explored the correlation between age-specific vaccination rates and cumulative incidence for the overall area
The results show that vaccinations during the influenza A(H1N1)pdm09 effectively reduced the cumulative incidence
Summary
In the 20th century, there were three influenza pandemics: the 1918–1919 Spanish flu (A/H1N1), the 1957–1958 Asian flu (A/H2N2), and the 1968–1969 Hong Kong flu (A/H3N2) [1]. 21st century, influenza A(H1N1)pdm began in Mexico and the USA in April 2009 and rapidly spread globally. In Japan, the first case of H1N1 infection was confirmed in May 2009, after which the disease spread quickly across the nation. Between May 2009 and August 2010, influenza A(H1N1)pdm affected approximately 21 million people and caused 203 deaths among 127 million people in the country [2]. Under abnormal situations such as the 2009 influenza pandemic, it would be beneficial to identify the route of infection, analyze pandemic dynamics and build a vaccination strategy to safeguard against the pandemic. Avoiding infection has an impact on medical and economic burden [3]
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