Every year, around February or March, the World Health Organization provides its recommendations on the composition of influenza vaccines for the northern hemisphere for the next flu season, based on its projections of what viruses are likely to be in circulation. But it’s hard to predict just how effective the vaccines will be.
In general, flu vaccines are around 50 per cent effective. But for the 2014-15 season, the vaccine effectiveness against H3N2 was less than 10 per cent. Flu shots are by no means perfect, but they’re still considered the best way of protecting people from getting sick.
The trivalent flu vaccine given this year, which contains three components, is comprised of an H1N1 vaccine component, an H3N2 component, and an influenza B component.
While the H1N1 component in this year’s flu shot has been updated for the coming season, the other two components have remained unchanged from last year’s flu vaccine, Skowronski says. Depending on which is the dominant strain this year, this could spell trouble.
“If it turns out to be a H3N2 season, then that means the vaccine effectiveness is likely to be suboptimal,” she says. That’s because last year, with the identical component, the vaccine effectiveness for H3N2 was around 35 to 40 per cent. And since the viruses are constantly changing and mutating, Skowronski says it’s unlikely the effectiveness of the same vaccine component will be any higher for the coming season. “That’s one of the unfortunate, concerning factors, frankly, from my perspective: that the H3N2 component is unchanged, yet we know the virus is changing.”
Even so, just because this year’s flu shot contains two out of three of the same components as last year’s, don’t think you won’t need to get vaccinated again if you got the shot last year. The updated influenza A component may help protect you in an influenza A outbreak, Warshawsky says. Plus, she adds, “We also know that the duration of protection doesn’t necessarily last well from one year to another. So relying on last year’s vaccine will not necessarily carry over protection to this year.”
The amount of information covered in the Globe and Mail’s article is really, really impressive. I learned a lot about the flu, vaccination, and how different vaccines interact with flu. Highly recommended.