Longtime readers know I've balked at getting a flu shot for decades.
The main concern is whether or not it's really effective. I get it... It's hard to consider getting a shot that might only have a 19% chance of really preventing the flu.
But many of you know that I changed my mind in 2017 when I saw new research showing that the flu vaccine can provide heart protection.
So this year, with so many headlines screaming about the "twindemic" of COVID-19 and the flu, I thought I'd take the time to explain my thinking on the flu shot and whether or not it's worth getting this year.
How does the flu shot work?
The influenza virus mutates very quickly – more so than many other viruses. So every year, researchers have to predict which strains we're most likely to face in the coming flu season. They use those strains to create a vaccine.
When our bodies encounter the virus from the vaccine, it triggers a mild response. Our bodies make antibodies to that particular virus. Antibodies work by patrolling the body. They've learned how to stick to the virus's outer shell proteins (called hemagglutinin or HA). So if our bodies see invaders with that same (or similar) HA protein, the antibodies attach to it and send out signals to come kill that invader. That way, your body can attack and kill new virus particles quickly, even before you have too many symptoms.
Why is it not 100% effective?
Because the flu virus mutates so quickly, researchers aren't often that accurate with their predictions. Sometimes they get close, and other times they miss by a wide margin. So your shot could be anywhere from 60% effective (the 2010 to 2011 season) to 19% effective (the 2014 to 2015 season). On average, over the past 10 flu seasons, it has been about 48% effective.
In the 2019 to 2020 season, influenza B viruses were more common early on. Then, as the season progressed, we saw a lot of influenza A strains, particularly H1N1. This year's vaccine contains those most commonly seen strains, including a type of the H1N1pdm09 that we saw in 2019.
So ideally, the vaccine strains would be a close match to the strains that circulate in the population that coming season. That means your antibodies should have no trouble recognizing the virus again, and your body would kill any infecting particles before you get sick.
But even if the strains aren't a close match to the vaccine, you'll still have partial immunity. This is cross-reactivity. It means your antibodies can still stick to the virus, but maybe not as well. Remember those HA proteins? Well they also change as the virus mutates... So we lose effectiveness in our vaccine-created antibodies.
So what's the real point of only having partial immunity? Can I still get the flu?
Yes, you can still get the flu even if you've gotten the vaccine. But it turns out that if you get the vaccine, you're far less likely to wind up with complications or to need hospitalization. This is true even if the vaccine's virus isn't the exact same as the one that's in the general population. We've seen several studies showing this:
A 2017 study from the Journal of Infection showed that with the vaccine, adults were about 40% less likely to need hospitalization if they got the flu. And according to a study in Vaccine, if you do wind up in the hospital, vaccinated folks are 59% less likely to need intensive care.
So it'll keep me out of the hospital. What's this about heart protection, too?
The flu takes a tremendous toll on the body, and especially puts a massive strain on your heart. Fighting off influenza activates your immune system. And when you're fighting off the virus, inflammation increases, particularly in your blood vessels.
More and more studies show that increases in inflammation lead to blockages... which ultimately leads to heart attacks or strokes.
What's more, the flu can cause your blood vessels to leak fluid, which builds up in your lungs. That can quickly lead to less oxygen in your blood, putting a strain on your heart.
We know that infection from the flu increases your risk of heart attack, and this is likely why. A 2018 study found that for a seven-day period after a flu diagnosis, people are six times more likely to suffer a heart attack.
The study looked at hospitalizations for heart attack for folks who had the flu. During one year before and one year after the flu diagnosis, the rate for hospitalizations was about 3.3 admissions per week. But for that one week after the flu diagnosis, admissions jumped to 20 per week.
Of course, your risk of heart attack is higher if you have existing conditions like diabetes or high blood pressure, as many folks in this study had. But what about the general population?
Well, a study earlier this year from the Annals of Internal Medicine found that out of 80,000 folks hospitalized for the flu between 2010 and 2018, one in eight had a "sudden, serious heart complication."
So lowering your risk with a flu shot makes sense for most older folks, especially with other risk factors.
So... most folks? Does that mean you don't recommend the vaccine for everyone?
For now, I still believe that if you're a young and healthy adult – without heart disease risk factors – chances are you don't need the flu vaccine. But if you're older and in less than Olympic fitness and health, you should do what I do and get a flu shot. That includes:
- Folks age 65 and older
- Those with a compromised immune system (including autoimmune diseases like Crohn's disease and those undergoing cancer treatments)
- Those who have heart disease or are at risk of heart attack
- Pregnant women
- Babies and young children
Similarly, if you're around someone who falls into one of these groups, consider getting a vaccine. For instance, if you're caring for someone recovering from chemotherapy, you don't want to risk exposing them. Complications for these folks can be life-threatening or fatal.
And to that list, I'd add that if you're at higher risk for COVID-19 (obese and diabetic), you should also consider getting vaccinated. I expect we'll continue to see more cases of COVID-19 as we head into colder weather and the cold and flu season. So protecting yourself against the flu makes sense. Hospitals will likely see an increase in patients, and that's the last place you want to go if you get a full-blown influenza infection. So consider that as well when deciding to get a flu shot.
As always, I want to hear from you, whether it's about the flu, vaccines, COVID-19, or anything else. Don't hold back. Send any questions and comments to our e-mail: [email protected].
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Here's to our health, wealth, and a great retirement,
Dr. David Eifrig and the Health & Wealth Bulletin Research Team
September 24, 2020