The flu vaccine North Americans are receiving this year may not be providing full protection against the most dangerous virus strain around this season, the Centers for Disease Control and Prevention (CDC) says.
This year, the seasonal influenza ‘A’ H3N2 virus has been the most common in North America and approximately half of the cases analyzed were “drift” variants, meaning they’re not the strain of flu against which the vaccine protects.
Historically, when H3N2 is the most common virus, there have been more illnesses, hospitalizations and deaths than when other forms are dominant, the CDC wrote in a Dec. 4 press release.
Though this may prove dangerous this season, drift variants of the flu aren’t uncommon.
“It’s completely normal for the flu virus to mutate, it’s always doing that and what we do, what public health agencies do and the makers of the vaccines do, is they get recommendations from the World Health Organization for which strains should be included in the seasonal flu shot,” said Chuck Ferguson, communications manager for Wellington-Dufferin-Guelph Public Health.
“So based on the WHO’s recommendations, H3N2 is one of the most common types of influenza affecting Canadians so far this season.”
Health officials decide more than six months prior to the start of the flu season what the composition of the vaccine will be, based on predictions about what they expect to be the most dominant viruses. Ferguson explained that data from the flu season in the southern hemisphere is often used to help make those predictions.
The CDC said the 2014-15 northern hemisphere flu vaccine was created about a month before the drifted H3N2 viruses were discovered in late March.
However, even though the vaccine doesn’t protect specifically against the drifted H3N2 that seems to be most dominant, the flu vaccine will still help lessen the severity of symptoms, Ferguson said.
“The flu shot will protect you from all the regular variants of the influenza and will certainly reduce your symptoms if you catch a variant that’s not covered by the particular shot.”
Because the drifted form hasn’t moved far enough away from the vaccinated H3N2 strain, it is not yet a new virus and the vaccine will still have some impact, he added.
Those most at risk for the flu are also most at risk for the drift variant, Ferguson said. That includes infants, children, the elderly and people with chronic health conditions.
Ferguson said this year’s Canadian flu vaccines protect against H1N1 and H3N2 influenza ‘A’ viruses and one or two influenza ‘B’ strains.
As of Dec. 1, Public Health had distributed 80,450 doses to physicians, pharmacists, hospitals, long-term care homes and other institutions. That’s 6,000 more than at the same time last year, Ferguson said.
In its press release the CDC said it’s too early to say whether this is going to be a particularly severe flu season, but early data shows the year could be headed in that direction.
“We’re still saying the flu shot is the best way Canadians can prevent the flu,” Ferguson said. “It’s a very safe, tried and true method.”
Other preventative measures include regularly washing hands with soap and water or an alcohol-based hand cleanser, coughing or sneezing into a tissue or shirt sleeve, keeping hands away from one’s eyes, nose and mouth, and staying home when sick. Officials say those infected can spread the virus for one to four days prior to experiencing any flu symptoms.
