The flu vaccine is only 10 percent effective this year. Blame eggs.
The way we make vaccines isn’t a good match for the virus type circulating this year.
By Julia Belluz@juliaoftorontojulia.belluz@voxmedia.com
Updated Feb 2, 2018, 8:48am EST

The first data on how well the flu vaccine is working this season in North America has just been published — and it helps explain why everyone appears to be sick right now.

The study, from the journal Eurosurveillance, found that the flu vaccine was only 10 percent effective against H3N2 (the main flu subtype going around in the US this season) among adults aged 20 to 64 years old in Canada — the age group that made up the majority of participants in the study. The protection rate rose to 17 percent when considering all age groups.

In most adults, the study suggests the shot would only prevent 10 percent of H3N2 flu cases. So if 100 in 1,000 unvaccinated people develop flu, the number would drop to 90 in 1,000 among vaccinated people — a very small difference in flu risk between vaccinated and unvaccinated individuals. And more than 80 percent of confirmed US flu cases have involved H3N2.

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The first data on how well the flu vaccine is working this season in North America has just been published — and it helps explain why everyone appears to be sick right now.

The study, from the journal Eurosurveillance, found that the flu vaccine was only 10 percent effective against H3N2 (the main flu subtype going around in the US this season) among adults aged 20 to 64 years old in Canada — the age group that made up the majority of participants in the study. The protection rate rose to 17 percent when considering all age groups.

In most adults, the study suggests the shot would only prevent 10 percent of H3N2 flu cases. So if 100 in 1,000 unvaccinated people develop flu, the number would drop to 90 in 1,000 among vaccinated people — a very small difference in flu risk between vaccinated and unvaccinated individuals. And more than 80 percent of confirmed US flu cases have involved H3N2.

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Part of the reason has to do with ... eggs

There are a couple of reasons why it’s harder to vaccinate against H3N2. For one, the virus mutates as it moves through the population at a faster rate than other flu viruses — making it even harder to design a shot that matches the circulating virus.

ne other reason the flu vaccine tends to underperform in H3N2 years has to do with ... eggs. To produce the vaccines, manufacturers need to grow a lot of flu virus — and they discovered long ago that flu virus grows extremely effectively in eggs. So viruses are injected into fertilized hen’s eggs, incubated for several days while they replicate, then harvested from the eggs, killed (or inactivated), and purified to go into vaccines.

“It’s an antiquated process, but it’s time-honored,” Anthony Fauci, the head of the NIH’s infectious diseases division, explained. While flu vaccines developed with more modern (cell-based and recombinant) methods of production have been licensed in the US, it’s not yet clear they are more protective against flu than the egg-based vaccines.

Plus, no other cell system comes close to growing the flu virus as cheaply or efficiently as eggs, and the industry has invested a lot in the egg-production infrastructure. So, Fauci explained, “We are stuck in the [egg-based] way, and it’s tough to transition to a more modern technology.”

But lately, researchers have found that there are problems with the egg-based approach that specifically relate to H3N2.

“In the process of adapting virus to grow in eggs, that seems to introduce further changes to the [H3N2] virus, which may impair the effectiveness of the vaccine,” Belongia said. In other words, while growing the flu virus for vaccines, H3N2 mutates to adapt to the eggs, which seems to result in a vaccine mismatch.

Skowronski, whose research helped uncover the egg problem, thinks scientists will discover other reasons the flu vaccine sometimes underperforms. “I don’t think [egg-based production methods] tell the whole story,” she said, noting how complicated flu viruses — and our responses to them — are.

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https://www.vox.com/science-and-health/2...e-effectiveness