Nearly 100 per cent of children are immune to measles, mumps and rubella after receiving two doses of the vaccine. But with the flu, it’s a much different story. The virus mutates year to year, and vaccines must be created to deal with what are believed to be the strains in circulation. The predominant flu strain that is causing illness in Canada this year is influenza A subtype H3N2.
The flu virus looks like a beach ball that’s covered with tree-shaped proteins called hemagglutinin. The “leaves” of the tree lock into our cells, which causes us to develop the flu. The influenza vaccine binds to the leaves, preventing the virus from getting in.
However, it’s possible that in any given year, there could be issues that affect how well the vaccine works. For instance, the vaccine may not bind effectively to the “leaves.” But researchers also say they don’t fully understand all of the variables involved.
“It’s more complex and I don’t think … we really have all the answers on that,” said Carolyn Pim, associate medical officer of health with Ottawa Public Health.
But scientists do believe that targeting different areas of the virus – namely the trunk or stem of the hemagglutinin, which remains stable year to year – is the key to developing a more effective flu vaccine that can be used against all strains and can provide immunity for years.
Despite the problems with the flu vaccine, people who are at risk of potentially deadly flu-related complications such as chest infections and pneumonia – namely the elderly and people with compromised immune systems – are urged to get it every year.
“Even though influenza vaccine is not as effective as other common vaccines, ‘not as effective’ does not mean ‘not effective,’ ” Thomas Talbot, chief hospital epidemiologist at Vanderbilt University Medical Center, wrote in the Journal of the American Medical Association this month.