Booster shots against COVID-19 are once again on my mind. The U.S. Food and Drug Administration says that older people and immunocompromised people are eligible for a second booster shot provided it has been at least four months since their last shot. After I got over the shock of the FDA calling me “older” — meaning anyone 50 and up — I’ve been pondering whether to get a second booster (otherwise known as a fourth dose of an mRNA vaccine, or third dose of any vaccine if you initially got the Johnson & Johnson vaccine), and if so, when.
Peter, a 60-year-old acquaintance who asked me not to use his last name to protect his privacy, told me he’s going to get a second booster, but not now. He’s holding out for fall and hoping for a variant-specific version of the vaccine. Right now, he and his wife “are vaxxed out,” he says. And he worries that getting boosted too often could hurt his immune system’s ability to respond to new variants. “I just think it’s the law of diminishing returns,” he says.
Lots of scientists and policy makers are thinking about these issues, too. For instance, last week an advisory committee to the U.S. Centers for Disease Control and Prevention met to discuss boosters. And a bevy of studies about how well boosters work and how they affect the immune system have come out in recent weeks, some of them peer-reviewed, some still preliminary.
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In making my own decision, I wanted to know several things. First, does a second booster really provide additional protection from the coronavirus beyond what I got from my first booster (SN: 11/8/21)? Second, are there downsides to getting boosted again? And finally, if I’m going to do it, when should that be and which vaccine will I get?
To get a handle on the first question, I need to know how much protection the first booster actually gave me. I’m not immunocompromised, so there’s no reason for me to get an antibody test to see if I have enough of those defenders to fend off the coronavirus. I just have to assume that my immune system is behaving normally and that what’s true for others in my age group also goes for me.
How long does COVID-19 booster immunity last?
Although the exact numbers vary, several studies have found that a third dose of the Pfizer COVID-19 vaccine gave higher levels of protection against the omicron variant than two doses did (SN: 3/1/22). But that protection wanes after a few months.
Data from Israel, where some people have been getting fourth doses for months, suggest that a second booster does indeed bolster protection, but again only temporarily. In health care workers who got a fourth dose, antibody levels shot up above levels achieved after the third jab, researchers reported April 7 in the New England Journal of Medicine. Vaccine effectiveness against infection was 30 percent with the Pfizer shot and 11 percent with Moderna. Both were better at preventing symptomatic disease, with Pfizer weighing in at 43 percent and Moderna at 31 percent. But those who did get infected produced high levels of the virus, suggesting they were contagious to others.
In a separate study published in the same journal, researchers looking at people 60 and older found that a fourth dose gave protection against both infection and severe disease, but the protection against infection began to decline after about five weeks.
There’s more data on protection against severe illness from a study of more than 11,000 people admitted for COVID-19 to a hospital or emergency department in the Kaiser Permanente Southern California health care system. At nine months after the second shot, two doses of the Pfizer vaccine were 31 percent effective at keeping people out of the emergency room with omicron, researchers reported April 22 in Lancet Respiratory Medicine. The shots were 41 percent effective at preventing more severe illness resulting in hospitalizations from the omicron variant.
The third dose (first booster) bumped the effectiveness way up to 85 percent against hospitalization and 77 percent against ER visits, the team found. But the effect was temporary. By three months after the booster, effectiveness had declined to 55 percent against hospitalization and 53 percent against emergency room visits. The same jump in protection and quick waning from the first booster has also been noted in the United Kingdom and Qatar.
It’s been about six months since my first booster shot, so any extra protection I got from it is probably gone by now. But will a fourth dose restore protection?
The CDC calculates that for every million people 50 and older who get a fourth dose of vaccine, 830 hospitalizations, 183 intensive care unit admissions and 85 deaths could be prevented. Those are impressive numbers, but many people think efforts should be focused more on getting still-unvaccinated people immunized instead of worrying about additional shots for the already vaxxed. CDC’s numbers support that. Because unvaccinated people are so vulnerable to the coronavirus, you would need to vaccinate just 135 people aged 50 and older with two shots to prevent one hospitalization. But already vaccinated people still have quite a bit of immunity, so you’d need to vaccinate 1,205 older people with a fourth dose to prevent one hospitalization.
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