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Federal health officials are urging Americans to boost their immunity before the winter holidays by getting a COVID-19 booster shot. But not everyone has the same defenses when it comes to keeping the virus at bay.
More than 47 million people in the US have already contracted the coronavirus, at least according to officially recorded figures. In reality, it’s probably many millions more.
An undetermined proportion of those people have also been vaccinated, meaning they now have what scientists call hybrid immunity. This is what happens when your immune system has essentially done both a dress rehearsal to fight off the virus – thanks to the vaccine – and a real feat – thanks to the virus.
So if you’ve already had a symptomatic case of COVID-19, do you really need a booster?
It probably comes as no shock that scientists are still not entirely sure. Boosters have not been available for most Americans for long, and the studies to understand how necessary they are for everyone — let alone for those who have been infected and vaccinated — are yet to be done.
But scientists say their best guess is that people with hybrid immunity already have better immunity than vaccinated people who never got COVID-19 or people who got COVID-19 but not the vaccine.
“It’s fair to say that your immunity will probably be stronger, so the chances of getting sick, especially with the delta variant, are very, very low,” says Dr. Duane Wesemann, an immunologist at Brigham and Women’s Hospital and Harvard Medical School.
Think of it like playing an instrument
Think of the immune system and coronavirus like you would learn an instrument: practice once and you’ll remember the song the next day, but if you stop, you probably won’t a year later. “The same principles apply to the immune system,” Wesemann says. “You’ll spend more time, more effort holding onto something you’ve seen multiple times.”
And if you are infected and vaccinated, that is already a lot of practice.
Just because you have this more robust immunity doesn’t mean it’s a bad idea to get a booster. This is especially true if you’re already predisposed to developing severe COVID-19, says John Wherry, director of the Institute for Immunology at the University of Pennsylvania.
All of this is still being studied, but Wherry says there’s no reason to think it would be risky for people with hybrid immunity to get an additional shot.
“The safety profile is quite similar during the primary vaccination course and boosters and it doesn’t seem to be very different depending on whether you had COVID before or not,” he says.
Our best picture of the power of hybrid immunity comes from studying humans who were infected and later vaccinated — what some scientists have even described as “superhuman immunity.”
“Looks like you’re already getting a pretty dramatic booster,” Wherry says. “They would probably be lowest on my priority list of who needs the booster injection.”
Research shows that people with this type of hybrid immunity produce more antibodies, and that this response is not only more stable, but also really robust between variants, says Wesemann, whose lab has studied the immune response in people who are infected and then vaccinated.
What if a person had a breakthrough infection?
So what about a person’s level of protection for the opposite scenario – when a fully vaccinated person later develops a breakthrough infection? “You would probably have superior immunity at this point,” says Dr. Gregory Poland, director of the Mayo Clinic’s Vaccine Research Group.
Most likely, this kind of hybrid immunity would rival what’s seen in people who recovered from COVID-19 and were subsequently vaccinated, but there could be subtle differences in the details of the immune response, Wherry says. “But these things that might be different might not matter to a particular person to ward off the next infection.”
All this needs to be studied in order to arrive at a more conclusive answer. Until then, the takeaway is the same no matter how you got to hybrid immunity: There’s no great urgency to get a booster for otherwise healthy and low-risk people. But if you’re at a higher risk because of underlying conditions, or if you live or work closely with someone who is, this can be a great extra protection for you and those around you.
“The potential benefits of increased immunity are there, and the risks are small,” Wesemann says. “I would probably recommend it for a group of individuals I thought were at high risk.”