Flu shot season, that time of year when signs go up in pharmacies and doctor’s offices advertising flu vaccines, seems to start earlier and earlier every year.
According to the CDC, flu vaccine shipments started in August this year and will continue through November, or until all of the vaccine is distributed.
This week, the American Academy of Pediatrics advised parents to get flu shots for all children ages 6 months and older as soon as the vaccine becomes available.
You may have thought, ‘Already? Isn’t it too early?’
Turns out, experts are interested in this question, too, because no one is sure how long the protection from flu vaccines actually lasts. There have never been any randomized clinical trials testing the duration of the flu vaccine’s effectiveness.
Some studies have tried to tease out a timeline of the flu vaccine’s effectiveness by comparing vaccinated versus unvaccinated patients who come to clinics with flu-like symptoms.
A 2018 analysis of these kinds of studies published in the Journal of Infectious Diseases found that the effectiveness of flu vaccine seems to decline significantly sometime between 3 and 6 months after you get the shot, particularly against certain strains, such as H3N2, the A strain that dominated much of last year’s severe flu season, and the B strains.
If you get your flu shot in early September, then, will it still keep you from getting sick in the spring if a flu season gets off to a late start or has a second, late peak?
For more insight on this, we reached out to William Schaffner, MD, an infectious disease expert at Vanderbilt University in Nashville.
WebMD: Is it possible to get a flu shot too early?
Schaffner: This turns out to be a much more complicated question that you would think at first glance. You’d be interested that this has been a matter of discussion in the [CDC’s] Influenza Vaccine Working Group for some time.
The data are mixed. Most of the data come from adults, and often older adults. There are investigators who are convinced that if you get the flu vaccine too early, there is evidence of waning protection by the time you get to February and March, which of course, is when you want to be protected.
On the other hand, there is the notion that a vaccine deferred is a vaccine not received. That frequently happens. The American Academy of Pediatrics certainly understands that. You don’t want to get to the peak of flu season and realize you forgot to get your child a shot.
For children under 8 years of age who are getting their flu vaccine for the first time, they need two doses separated by a month, so for them, it’s really a good idea to start a little early, right?
After saying all of that, there is a general sense that in some years, and this year was one of them, when vaccine manufacturers have been successful in delivering vaccine to large users, like pharmacies and hospital systems, vaccine can start coming in the end of July and August.
People such as myself — even though this is not an official recommendation — are wary of starting to vaccinate that early.
But now we’re into September, and it begins to get even more nuanced. I was asked yesterday, ‘Should I wait a couple of weeks?’
My sense was that this was someone who was going to get vaccinated, so I said ‘Yes. Wait until the end of September beginning of October.’
WebMD: Is that the ideal window?
Schaffner: If you asked me what the ideal was, it would be end of September through October to get vaccinated.
Particularly for older people and such, doing it in October, rather than August, is much better advised.
WebMD: Speaking of older people, I’ve been seeing ads on TV for the senior flu vaccine. Are they working as intended?
Schaffner: There are actually two vaccines licensed for people 65 and older. One is high-dose. The other is adjuvanted, meaning it has an extra ingredient that’s supposed to help it stoke the immune response. The vaccine effectiveness assessments in the population, large as they are, have not been sufficient to give us vaccine specific assessments in the field.
Both vaccines had clinical trial data to show they actually provide better protection for older adults over multiple seasons.
The CDC has not expressed a preference on either of these. Here in my own medical center we are promoting the use of those vaccines for adults age 65 and older.
My wife, who listens to me talk about the flu a lot, when she goes to the pharmacy to get her annual flu shot, she asks for high-dose. I think there are more and more people who are doing that. They’re both paid for by Medicare so there’s no cost out of pocket.
WebMD: How about pregnant women. Should they get a shot now, or wait a few weeks longer?
Schaffner: If you’re pregnant during flu season, you should definitely get vaccinated. There isn’t any doubt about that. There’s a dual benefit, for mom and the baby.
Pregnant women who get influenza have rates of complications from the flu — pneumonia, hospitalizations, etc. — that are comparable to those of seniors.
There are two or three reasons. The baby pushes up the diaphragm which compresses the lungs, that’s kind of a set up for pneumonia. Number two, they retain fluid in pregnancy. That, too, can predispose to pneumonia if you get a viral infection. Number three, women’s immune system is made more tolerate because you don’t want to reject the baby, and it’s thought that might make women more vulnerable because their immune system isn’t fighting as fiercely.
The bonus is that the protection her body makes cross the placenta and get into the baby.
There are now half a dozen or more studies to show that those babies during the first six months of life have some protection against influenza. That’s important because during those first six months we can’t directly vaccinate the baby.
It’s two for the price of one, if you will.
So if you’re pregnant, go get your flu shot, and take the rest of your family along with you because all the adults who are going to be around the baby need to be fully vaccinated to shield them from the virus.
If you’re pregnant and expect to deliver in September, get the shot now. If you’re delivering later in the year, you can probably wait a few weeks, too.