GlobalHealth Threats

The United States Centers for Disease Control and Prevention (US CDC) has found that the 2016-17 U.S. flu season was moderate overall, longer lasting than previous seasons and dominated by influenza A(H3N2) viruses. The season peaked in February, with influenza B viruses predominant after March and some influenza A(H1N1)pdm09 also detected.

In an article published in their Morbidity and Mortality Weekly Report (MMWR), the 2016-17 northern hemisphere flu vaccine was found to be 34% effective against A(H3N2) viruses and 56% against B viruses. The overall vaccine effectiveness was 42%, meaning that influenza related medical visits were on average reduced by over 40%. Influenza vaccines have higher protective rates when A(H1N1) or B viruses are circulating. Flu seasons dominated by A(H3N2) viruses tend to result in only modest vaccine effectiveness, and lead to increased hospitalisations and deaths, particularly in children under 5-years or adults over 65-years.

The authors propose a change to the H1N1 virus which should be used in the 2017-18 flu vaccine, which would match those that are included in the current 2017 southern hemisphere vaccine. They also found that the viruses in circulation showed no resistance to antiviral medications such as oseltamivir and zanamivir.