Flu vaccine only 23 per cent effective this season: CDC

Flu shot
File photo. File, Mary Ann Chastain, The Canadian Press

TORONTO – Health officials already warned that this year’s flu vaccine wasn’t an ideal match to combat the season’s nasty H3N2 virus. Now, U.S. scientists measured its potency: the vaccine was only 23 per cent effective.

In a new study released Thursday, Centers for Disease Control and Prevention scientists say the 23 per cent efficacy is among one of the worst results since they started tracking how well the vaccines work. Ideally, the best flu vaccines are 50 to 60 per cent effective.

Their findings are based on 2,300 people in five states who fell sick.

The northern hemisphere, more or less, uses the same vaccine – there are only miniscule variations by product and manufacturer.

READ MORE: Nasty H3N2 flu season worsens as cases rise across Canada

The Public Health Agency of Canada has already conceded that the vaccine isn’t “optimally matched” to protect against H3N2. In an emailed statement, an agency spokesperson said the Canadian situation mirrors the U.S.

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“To date, the available Canadian data estimates a low level of vaccine effectiveness against the H3N2 strain consistent with the U.S.,” the statement read.

PHAC says that in past years, Canadian vaccine effectiveness has been similar to American rates, too. Initial Canadian figures on effectiveness should be available at the end of January.

Public health officials across the board already warned of a vaccine mismatch, and braced for a busy flu season – H3N2 tends to affect its patients more, requiring more hospitalizations than people battling the virus at home.

Each year, strains of the influenzas mutate and re-emerge, infecting victims and triggering a new season. Those of us in the northern hemisphere keep a watchful eye over the flu in the southern hemisphere, which affects residents during their winter (or our summer).

READ MORE: Nasty flu season strikes as H3N2 cases spike across Canada

Scientists look at the patterns and make their predictions based on what viruses made their rounds below us and estimate what mutations could occur before the influenzas make their way over the equator.

Picking out three strains for a vaccine is guesswork, and by the time influenza makes its way into the northern hemisphere, it’s had time to mutate or “drift.” But by then, the flu vaccine is already formulated.

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This year, the vaccine isn’t as effective but health officials say it’s still worthwhile to roll up your sleeve and get the shot.

READ MORE: This year’s flu shot may not be the right match, CDC tells doctors

While it may not protect against this one strain of the flu, it’ll still fight against other strains floating around. It’ll also lessen the risk of complications.

“Though reduced, the cross-protection might reduce the likelihood of severe outcomes such as hospitalization and death,” the CDC advisory said to American doctors when it discovered the mismatch.

Read more about who should be vaccinated here.

Read the CDC report here.

– With files from Global News’ Kathlene Calahan and The Associated Press