Effectiveness of flu shot under 20 per cent for dominant strain this season: experts
File image of person receiving a flu shot.
The Canadian Press
Published Thursday, February 1, 2018 1:38PM EST
TORONTO -- Researchers say the effectiveness of this season's flu shot has been low, with the vaccine preventing only 10 to 20 per cent of infections caused by the dominant H3N2 strain affecting Canadians.
Lead researcher Danuta Skowronski of the BC Centre for Disease Control says that's in line with what Australia experienced during the southern hemisphere's flu season, which ended in late August as Canada's was about to begin.
Both Canada and Australia used the same vaccine components, which are meant to offer protection against two A-type influenza viruses -- H3N2 and H1N1 -- and a B strain.
The same vaccine was used last season in Canada and was found to be 42 per cent effective in preventing cases of H3N2 in this country. That suggests the virus has genetically mutated, making the vaccine less effective this year.
However, Skowronski says the flu shot was 55 per cent effective overall in preventing cases of the respiratory illness caused by the dominant B strain of influenza also affecting Canadians this season.
The mid-season estimates for Canada by a network of influenza researchers across the country are published in the online journal Euro Surveillance.