How long does immunity to COVID-19 last?


Odds are, you had COVID-19 whether you knew it or not. Nearly 60% of people in the United States have antibodies in their blood that suggest they have been infected with SARS-CoV-2, the virus that causes COVID-19, according to new estimates from the Centers for Disease Control and Prevention from the United States.

But that doesn’t mean 60% of people in the United States are immune to COVID-19. “We know that’s not what it means. Reinfection happens,” said Dr. Kristie Clarke, co-lead of the CDC’s COVID-19 Epidemiology and Surveillance Task Force Seroprevalence Team, during an April 26 press briefing. . “Protection against vaccination and protection against previous infections decrease 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 stay free after an injection or illness. Here’s what the latest science says about immunity to COVID-19.

If I already had COVID-19, will I catch 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 over by the virus.

A study by British researchers published in the New England Journal of Medicine in March found that infection-related immunity remains strong for up to a year and then began to decline, while the protection afforded by two doses of a Pfizer-BioNTech vaccine begins to decline at around six months. Meanwhile, a research review published in the Annals of Internal Medicine in April concluded that people who had recovered from COVID-19 had significant protection against reinfection for at least seven months.

But all of this research was done before the emergence of the Omicron variant, which is more contagious than previous strains. “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, professor of medicine at Oregon Health & Science University.

According to a new study by researchers at the Indiana University School of Medicine, children can retain their antibodies even longer than adults. Six months after infection, more children than adults still had antibodies capable of neutralizing the virus, they found.

While these findings should bring 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 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 to say for sure how long someone who has recently recovered from COVID-19 can stop getting sick. worry about being reinfected. But, he admits, it would be “highly unusual” to catch 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 they are different from those the body naturally produces.

Vaccines provide strong, long-lasting protection against serious illness and death, but their effectiveness against infection decreases over time, so your risk of getting sick is lowest soon after your last dose. A research review published in the Lancet in March analyzed data from previous studies that assessed the effectiveness of different COVID-19 vaccines, including those made by Moderna, Pfizer-BioNTech, AstraZeneca and Johnson & Johnson. Regardless of brand, the ability of vaccines to prevent symptomatic disease dropped by 20 to 30 percent after six months, the researchers found, although they remained effective in preventing severe illness and death. This review was also published before the Omicron variant – against which vaccines are less effective – began to become widely available.

Even with Omicron in circulation, however, 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 is unvaccinated, whether they have had COVID-19 or not, should still get vaccinated, says Dr. Jessica Ridgway, associate professor of medicine at the University of Chicago and study co-author recent report 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 provide even higher levels of protection.

What if I’m vaccinated and had COVID-19?

If you have recovered from COVID-19 and received a COVID-19 vaccine, you have what is called “hybrid immunity”. Studies suggest that this type of protection is better than vaccination or exposure alone, because you benefit from both natural and vaccine-derived defenses.

“The best immunity, without a doubt in my mind, is hybrid immunity,” says Farber.

Of course, you should never try to catch COVID-19 for the purpose of getting hybrid immunity. Although it is very unusual for a vaccinated and generally healthy person to have a severe case of COVID-19, complications can occur. People have contracted Long COVID even when fully vaccinated and showing few symptoms, for example.

Will I need to continue receiving COVID-19 boosters forever?

The U.S. 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 general population, but there has been much speculation as to whether they will, as vaccine-related immunity wanes over time.

The FDA’s Vaccine Advisory Committee met in April to discuss ways to streamline and improve the recall strategy going forward. An annual dose, as with influenza vaccines, is a possibility, but the SARS-CoV-2 virus mutates in a less predictable way than the influenza virus, so it is difficult to prepare in advance a booster that would target the strain that will circulate later.

A better model might be to develop boosters that provide multi-variant immunity. This science is underway now, but it’s too early to tell exactly what future stimulus strategies will look like.

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Write to Jamie Ducharme at jamie.ducharme@time.com.


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