Flu vaccine to underperform again

Epidemiologist expects less than ideal protection against resurgent H3N2 flu strain but better than 'zero' last year

There are signs the flu season may hit B.C. early and hard and public health officials are warning they expect the flu vaccine to again be less effective than they’d like.

The most dangerous influenza type for vulnerable people is the H3N2 strain that was dominant in last year’s severe flu season.

But because of a genetic mismatch, the vaccine provided last year was useless in warding off H3N2, according to B.C. Centre for Disease Control epidemiologist Dr. Danuta Skowronski.

That component of the vaccine was replaced on orders of the World Health Organization, but preliminary evidence suggests the new version will still not be a good match against H3N2, falling well short of the 60 to 70 per cent protection rates against other flu strains in most years.

“I believe it’s going to be better than last year – in other words I don’t think it’s going to be zero – but by how much, I can’t say,” Skowronski said.

She said there’s good reason to hope it may be 40 to 60 per cent effective overall, adding she continues to recommend the vaccine, particularly for those more vulnerable.

“If you are a high-risk person, especially with heart and lung conditions or elderly, even if you’re looking at vaccine protection of 30, 40 or 50 per cent, you’re still better off than if you’re unvaccinated.”

Flu vaccine will be widely available by November and may be offered sooner than that in high-risk settings like residential care homes.

Epidemiologists had expected H3N2 would be less prevalent this year, with more of a mix of H1N1 and influenza B strains also in circulation, making the mismatch less of a worry.

But Skowronski noted there have already been two H3N2 outbreaks in long-term care homes in B.C.’s Vancouver Coastal health region – one in the summer and another in late September.

“To have had outbreak activity already in the summer is very unusual,” she said. “We are monitoring that closely for the possibility of an early season.”

Apart from last year, B.C. hasn’t seen flu outbreaks this early since 2009.

Last year, with H3N2 widespread and the mismatched vaccine offering no defence, there were 175 outbreaks in long-term care homes.

That was the highest number in more than a decade and twice as many outbreaks as the previous peak year of 2012.

Skowronski acknowledged the mismatch problems threaten to erode public confidence in the flu vaccine but hopes vulnerable patients are not dissuaded.

“For me, it would be a double tragedy, frankly, if coming out of last season our high-risk people lost faith and did not get the vaccine.”

While influenza is a “miserable” illness, Skowronski said it’s not life-threatening to healthy people, for whom vaccination is still encouraged but a matter of personal preference.

About one-third of B.C. residents typically get the flu vaccine each year.

H3N2 vaccines have consistently underperformed in recent years.

Skowronski said more work is needed to try to solve the challenges of accurately gauging the vaccine’s fit against the virus in the lab, and in effectively reproducing a well-matched vaccine without losing its properties.

Also requiring more research, she said, is emerging evidence suggesting repeated use of the vaccine by a given patient diminishes its effectiveness for them in future years.

While the flu vaccine may not perform as well for someone who also received it the previous year as it would for a first-time user, Skowronski said, they’ll still be better off than unvaccinated people.

Her team is trying to recruit more B.C. doctors and nurses to help track the spread of flu strains this year and monitor the effectiveness of this year’s vaccine.