TORONTO (CP) ó This yearís flu shot offered moderate protection against one type of influenza virus circulating in North America, but no protection against the main strain that has been afflicting Canadians in the tail end of the flu season, new research suggests.Quote has been trimmed
An interim look of the efficacy of this yearís flu vaccine showed it had zero impact on the main strain of influenza B viruses circulating this winter, called B/Florida-like viruses.
In recent weeks influenza B cases have been on the upswing in parts of Canada. In fact, while the influenza A subtype H1N1 was the predominant strain earlier in the flu season, a recent surge in flu B infections means those viruses are on the verge of overtaking H1N1 as the main source of flu illness in the country this year.
Flu vaccine, which has to be reformulated every year because the viruses mutate constantly, is made to protect against three strains of flu: the influenza A subtypes H1N1 and H3N2 and one type of influenza B virus.
Experts gather at the World Health Organization months in advance of flu season to make best guesses about which virus families within each of those three types are likely to be the major causes of disease the following winter. When they gathered in February 2007 to make choices for the 2007-2008 flu shot, they missed the mark for both the H3N2 and influenza B viruses.