Eggs may be to blame for the low effectiveness of the flu shot

Posted at 11:50 PM, Feb 08, 2018
and last updated 2018-02-09 09:43:50-05

This flu conundrum will really scramble your mind: chicken eggs may be at least partially to blame for this really bad flu season!

In recent studies from Australia and Canada, the flu shot was shown to be as little as 10-percent effective against the flu this year, depending on the age of the patient. It’s an early prediction, but flu season could drag on until May, according to the U.S. Centers for Disease Control and Prevention.

That alarming percentage is applicable to working-age adults—people ages 20 to 64 years old—so the effectiveness could change if you add in the entire population, according to a report from Vox. The vaccine’s overall effectiveness was estimated at 17 percent, according to a study out of Australia.

So what does any of this have to do with eggs? It starts with how the vaccine is produced.


flu shot photo
Getty Images | Spencer Platt


How The Flu Vaccine Is Made

To produce the flu vaccine, you must first grow the virus. I was surprised to learn that viruses are most commonly injected and grown in eggs. The process is cheap and has been used for about 70 years.

A particular strain of the flu is injected into fertilized eggs, incubated and harvested. The virus is then killed or purified before being added to vaccines.


eggs photo
Getty Images | Justin Sullivan


It’s not a perfect process but it’s what doctors and scientists have relied on for years. What makes this year particularly tricky is the strain circulating globally this season: H3N2, a strain of the influenza A virus. It apparently mutates at a higher rate compared to other strains.

Flu viruses will constantly mutate on their own, which is why a flu vaccine is so difficult to develop in the first place. But in the comfy environment of its own little egg, H3N2 is prone to mutation as it adapts to the egg, according to Vox. Since the virus itself changes during the process, the vaccine may become ineffective. This is a particularly burdensome problem with H3N2.

Eggs Aren’t Completely To Blame

Eggs are far from the only challenge in developing a vaccine. Forbes reports it can take five to six months to develop a batch of influenza vaccines. Starting in February, flu experts have to start predicting which flu strains will be circulating by October, the start of the following flu season.

Health experts in the U.S. will use data from Australia and other parts of the world to piece together information to develop the best vaccine for a particular flu season. That process has its own set of uncertainties. According to the Vox report, vaccine manufacturers may prepare for one combination of viruses to spread—but if different strains end up circulating, the vaccine will not work.


Swine Flu Vaccinations Get Under Way In Germany
Getty Images | Andreas Rentz


It gets worse. According to the CDC, vaccine effectiveness can also vary among different age groups. Flu viruses change constantly, even over the course of a single flu season. That means a vaccine may be effective in one city, but less effective in another if the strain changes by the time it crosses the country.

Right now, the CDC says egg-based is the production method of choice for most current flu vaccines. There are other methods out there—one uses an insect virus grown in caterpillar cells, according to NBC News—but the industry overall has yet to shift from the egg-based approach.

There’s also hope for a universal vaccine, one that would protect against all influenza viruses. That would be a true game changer.

Why Get The Flu Shot This Season?

With a lousy chance of being protected against H3N2 this year, why get the flu shot? Well, it’s better than no protection at all, especially when the virus is basically everywhere. Since October, the CDC says nearly 15,000 people have been hospitalized with confirmed cases of influenza. All but two U.S. states have reported widespread flu activity.

Plus, your getting the flu shot means better protection for the most vulnerable people: children and the elderly.

When it comes to getting the flu shot, better late than never is this year’s motto, especially given that flu season could still go on for months. Did you get yours?

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