Odds are, you’ve had COVID-19—whether you know it or not. Almost 60% of people in the U.S. have antibodies in their blood that suggest they’ve been infected by SARS-CoV-2, the virus that causes COVID-19, according to new estimates from the U.S. Centers for Disease Control and Prevention.
But that doesn’t mean 60% of people in the U.S. are immune to COVID-19. “We know that is not what this means. Reinfection happens,” said Dr. Kristie Clarke, co-lead for the CDC’s COVID-19 Epidemiology and Surveillance Taskforce Seroprevalence Team, during a press briefing on April 26. “Protection from vaccination and protection from previous infections does wane over time.”
Two years after the outbreak, there are millions of people infected. Researchers continue to learn more about how the virus affects immunity and what time you can expect not to get sick from it. Here’s what the latest science says about immunity to COVID-19.
Will I be able to get COVID-19 again if I have had it before?
Your immune system mounts a few different defenses against SARS-CoV-2. The invader is defeated by white blood cells known as B cells. These antibodies are produced by antibody proteins. T cells are another form of white blood cells and can destroy cells infected by the virus.
Study by U.K. researchers, published in New England Journal of Medicine in March found that infection-related immunity stays strong for up to a year, then began to wane—whereas the protection offered by two doses of a Pfizer-BioNTech vaccine begins to wane at around six months. In the meantime, research was done in and published in Annals of Internal Medicine in April concluded that people who’d recovered from COVID-19 had significant protection against reinfection for at least seven months.
All of this research took place before Omicron, which has a higher contagious strain than the previous ones. “We can’t really predict how the protection will work for the next variant or over a period of time,” says co-author Dr. Mark Helfand, a professor of medicine at the Oregon Health & Science University.
According to new research from the Indiana University School of Medicine, children may retain their antibodies longer than adults. The researchers found that more children than adults had antibodies capable to neutralize the virus six months later.
These results should provide some comfort for those who have suffered from COVID-19. But, immunity is not guaranteed. One Spanish woman was recently featured for being positive for COVID-19 in two separate tests, which were performed within 20 days. Different people have different levels of antibody after infection. It’s also not clear exactly how antibody levels correlate with protection against infection, so a positive antibody test doesn’t necessarily mean you’re immune to the virus, Clarke said during the CDC briefing.
Dr. Bruce Farber, chief of infectious diseases at Northwell Health in New York, says there’s no way to say for sure how long someone who has recently recovered from COVID-19 can stop worrying about being reinfected. But, he allows, it would be “very unusual” to get COVID-19 within 90 days of a previous case.
If I’m fully vaccinated, am I immune to COVID-19?
COVID-19 vaccines also prompt the body to produce antibodies and trigger a T-cell response, though they’re different from those the body produces naturally.
Although vaccines offer strong, long-lasting protection from severe diseases and death, their effectiveness against infections decreases over time. This means that your chance of becoming sick after the last dose is completed. In a research review, Lancet in March analyzed data from prior studies that assessed the effectiveness of different COVID-19 vaccines, including those made by Moderna, Pfizer-BioNTech, AstraZeneca, and Johnson & Johnson. Across brands, vaccines’ ability to prevent symptomatic disease dropped by 20% to 30% after six months, even though they remained good at preventing severe disease and death, the researchers found. This review was also published before the Omicron variant—against which vaccines are less effective—began spreading widely.
Even with Omicron circulating, however, someone who’d been vaccinated was 2.4 times less likely to test positive for the virus in March than an unvaccinated person, according to the CDC.
Anyone who is unvaccinated, whether they’ve had COVID-19 or not, should still get their shots, says Dr. Jessica Ridgway, an associate professor of medicine at the University of Chicago who co-authored a recent study on COVID-19 reinfection. “They’re incredibly safe and having that additional level of immunity would definitely be helpful for preventing COVID,” she says. A booster dose may also be beneficial in protecting against COVID, according to research.
What if I’m vaccinated And Was COVID-19 available?
If you’ve recovered from COVID-19 and gotten a COVID-19 vaccine, you have what’s known as “hybrid immunity.” Studies suggest this type of protection is better than either vaccination or exposure alone, because you benefit from both natural and vaccine-derived defenses.
“The best immunity, no question in my mind, is hybrid immunity,” Farber says.
However, it is not a good idea to try and catch COVID-19 just for hybrid immunity. While it’s very unusual for someone who is vaccinated and generally healthy to have a severe case of COVID-19, complications can happen. People have gotten Long COVID even when they’re fully vaccinated and experience few symptoms, for example.
How long will I be able to get COVID-19 boosters for?
Recently, the U.S. Food and Drug Administration approved a second round for boosters to people 50 years and over. It also authorized some immunecompromised individuals across all age groups. Additional boosters haven’t yet been authorized for the entire population—but there’s been lots of speculation about whether they will be, since vaccine-related immunity wanes with time.
The FDA’s vaccine advisory committee met in April to discuss ways to streamline and improve booster strategy moving forward. An annual dose, as with flu shots, is a possibility—but the SARS-CoV-2 virus mutates in less predictable ways than the influenza virus, so it’s challenging to make in advance a booster that would target whatever strain is circulating later on.
It is possible to develop boosters which provide multiple-resistant immunity. This model would be a superior one. That science is underway now, but it’s too soon to say exactly what future boosting strategies will look like.
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