A man adjusts a COVID-19 testing tent in New York City on April 27, 2022. Credit: Spencer Platt/Getty Images
You most likely have had COVID-19, whether you know it or not. Nearly 60% of people in the US have antibodies in their blood that suggest they’ve been infected with SARS-CoV-2, the virus that causes COVID-19, according to new estimates from the Centers for Disease Control and Prevention. and US Disease Prevention.
But that doesn’t mean that 60% of people in the US are immune to COVID-19. “We know that is not what this means. Reinfection happens,” said Dr. Kristie Clarke, co-leader of the Seroprevalence Team of the CDC’s COVID-19 Surveillance and Epidemiology Task Force, during an April 26 news conference. “Protection from vaccination and protection from previous infections decline over time.”
Even two years and millions of infections into the pandemic, researchers are still learning about immunity to the virus and how long you can expect to remain disease-free after a vaccine or illness. Here’s what the latest science says about immunity to COVID-19.
If I already had COVID-19, will I get it again?
Your immune system mounts a few different defenses against SARS-CoV-2. White blood cells called B cells produce antibody proteins, which help fight off the invader. Meanwhile, T cells, another type of white blood cell, can kill cells that have been taken up by the virus.
A study by UK researchers published in the New England Journal of Medicine in March found that immunity linked to infection remains strong for up to a year, then begins to wane, while the protection offered by two doses of a Pfizer-BioNTech vaccine begins to wane at around six months. Meanwhile, a research review published in the Annals of Internal Medicine in April it concluded that people who had recovered from COVID-19 had significant protection against reinfection for at least seven months.
But all of that research was done before the appearance of the Omicron variant, which is more contagious than earlier strains. “We really can’t 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 Oregon Health and Science University.
Children may retain their antibodies even longer than adults, according to a new study from researchers at the Indiana University School of Medicine. Six months after infection, more children than adults still had antibodies capable of neutralizing the virus, they found.
While those findings should provide some comfort to people who have had COVID-19, there are no guarantees when it comes to immunity. (A woman in Spain recently made headlines for testing positive for COVID-19 twice, just 20 days apart.) Some people develop more antibodies after an infection than others. It’s also unclear 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 of knowing for sure how long someone who recently recovered from COVID-19 can stop worrying about getting infected again. But, he admits, it would be “very unusual” to contract COVID-19 within 90 days of a previous case.
If I am fully vaccinated, am I immune to COVID-19?
COVID-19 vaccines also prompt the body to produce antibodies and trigger a T-cell response, although these are different from the ones the body produces naturally.
Vaccines provide strong, long-lasting protection against serious illness and death, but their effectiveness against infection declines over time, so your risk of getting sick is lowest soon after your most recent dose. A research review published in the lancet in March analyzed data from previous studies evaluating the effectiveness of different COVID-19 vaccines, including those made by Moderna, Pfizer-BioNTech, AstraZeneca and Johnson & Johnson. Across all brands, the vaccines’ ability to prevent symptomatic disease fell by 20% to 30% after six months, although they were still 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, became widely available.
However, even with Omicron in circulation, someone who had 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 isn’t vaccinated, whether or not they’ve had COVID-19, should still be vaccinated, 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 are incredibly safe and having that extra level of immunity would definitely be helpful in preventing COVID,” she says. Plus, research shows that getting a booster dose can help take protection to even higher levels.
What happens if I am vaccinated? Y had COVID-19?
If you have recovered from COVID-19 and received a COVID-19 vaccine, you have what is known as “hybrid immunity.” Studies suggest that this type of protection is better than vaccination or exposure alone, as it benefits from both natural and vaccine-derived defenses.
“The best immunity, hands down, is hybrid immunity,” says Farber.
Of course, you should never try to get COVID-19 to get hybrid immunity. While it is highly unusual for someone who is vaccinated and generally healthy to have a severe case of COVID-19, complications can occur. People have caught prolonged COVID even when fully vaccinated and experiencing few symptoms, for example.
Will I have to keep getting COVID-19 boosters forever?
The US Food and Drug Administration (FDA) recently authorized a second round of boosters for people age 50 and older, as well as some immunocompromised people in all age groups. Additional boosters have not yet been authorized for the entire population, but there has been much speculation as to whether they will be, as vaccine-related immunity wanes over time.
The FDA’s vaccine advisory committee met in April to discuss ways to optimize and improve the booster strategy going forward. An annual dose, as with flu shots, is a possibility, but the SARS-CoV-2 virus mutates less predictably than the influenza virus, so it’s challenging to do a booster ahead of time that target any strains that are circulating further ahead.
A better model might be to develop boosters that provide immunity to multiple variants. That science is underway now, but it’s too early to say exactly what future momentum strategies will look like.