Vaccine effectiveness against virus strain A(H3N2) for 2016/17 season among hospitalized elderly people was 17%. Among those who also received vaccination the previous season, the vaccine effectiveness was -2% (negative).
Authors expect that next season it will not be particularly effective either, due to the fact that the virus strain used in the vaccine 2017/18 - A(H3N2) – remained unchanged.
The article explains why the vaccine for 2016/17 season was not effective (virus growing in eggs and mutating).
During the season 2014/15 effectiveness of the vaccine against flu type A(H3N2) in Canada was estimated at 53% for those who got vaccinated that year. Among those who had been vaccinated the previous year, the effectiveness was negative -32%. Among those who were vaccinated third year in a row, the vaccine effectiveness was negative -54%. The average vaccine effectiveness was -17% (negative).
Influenza type A(H3N2) vaccine effectiveness during 2004-2013 was 65% for those who got vaccinated that season. In those who are vaccinated frequently, the effectiveness was 24%. The effectiveness of type B flu virus was 75% for those vaccinated that season, and 48% for those who are vaccinated frequently.
Research over the course of 8 seasons (1999-2007) shows a threefold increased risk of hospitalization in subjects who did get the trivalent inactivated flu vaccine, vs. unvaccinated subjects.
During these 8 seasons strain A(H3N2) was wrongly guessed 5 times; strain A(H1N1) and B – 4 times.