Only 50 people are known to have contracted COVID-19 more than once, but the new strains have medical experts on high alert


It is very rare for someone to become infected with the coronavirus that causes COVID-19 disease a second time, but the few confirmed cases of reinfection tell us that immunity to the virus is not guaranteed and that vaccination could become a regular part of our life. medical care. careful in the future.

There are around 50 confirmed cases of reinfection worldwide. That is far less than 1% of the 110 million reported coronavirus cases worldwide. BNO News, a Dutch news site, is tracking reinfections globally; 51 confirmed cases of reinfection have been identified along with approximately 11,000 suspected or probable reinfections.

Reinfection is believed to occur when protective antibodies are lowered in people who have previously contracted the virus or in people who contracted the virus without developing antibodies.


“I don’t think anyone had the expectation that if you had COVID and got over it, you could never have it again.”


– Dr. Bruce Polsky, NYU Langone

For some infectious disease doctors, this is not a surprise.

“I think everyone anticipated that there would be reinfections at some distant point after the initial infection,” said Dr. Bruce Polsky, an infectious disease physician at NYU Langone Hospital on Long Island. “I don’t think anyone had the expectation that if you had COVID and got over it, you could never have it again.”

The Centers for Disease Control and Prevention defines reinfection as a positive COVID-19 test that occurs at least 90 days after an initial positive test. (This is to differentiate you from people with persistent “long-term COVID” symptoms). The public health agency says reinfection is rare; however, he also says that he expects the number of reinfections to increase as the pandemic continues.

“The probability of reinfection with SARS-CoV-2 is expected to increase over time after recovery from the initial infection due to decreased immunity and possibly genetic drift,” the CDC said in October.

As the pandemic moves into its second year, this could put some of the roughly 27 million people in the US who have already had COVID-19 at risk of contracting it again.

The duration of the pandemic, along with the emergence of the new, more infectious variants B.1.1.7 and B.1.351, may also put people at risk for a second SARS-CoV-2 virus infection. The CDC has said that the B.1.1.7 strain, which has been confirmed in 1,523 Americans, as of February 16, may become the most dominant form of the virus in the US by the end of March. Variant B.1.351, first identified in South Africa, has been detected in 21 people in the US.

“Yes [B.1.351] becomes dominant, the experience of our colleagues in South Africa indicates that even if you have been infected with the parent virus, there is a very high rate of reinfection to the point where the previous infection does not appear to protect you against reinfection, ”said Dr. Anthony Fauci, medical adviser to President Joe Biden and longtime director of the National Institute of Allergy and Infectious Diseases, told CNN earlier this month.

What is medical research telling us about immunity right now?

Studies on reinfection have had mixed results so far. (Several projects studying reinfection have recently been announced, including one at the Indiana University School of Public Health in Bloomington that tests for COVID-19 reinfection in US hotspots and an observational study that it plans to evaluate. all reinfections reported in France).

A recent preliminary study examining marine recruits arriving at a base on Parris Island in South Carolina found that a previous infection with SARS-CoV-2 protected them against re-infection, but only to a limited extent. Marines with lower IgG antibody titers and neutralizing antibodies had a higher risk of reinfection, the researchers concluded.

Other research underscores the rarity of reinfection. Researchers in Qatar found that less than 1% of the roughly 44,000 people who had recovered from a COVID-19 case contracted SARS-CoV-2 a second time.

But beyond the risk of reinfection, there are a number of factors that can influence immunity to the SARS-CoV-2 virus.


“Since it is not known how long immunity will be induced, we have the possibility that, as the virus continues to mutate, it will mutate to become a cold virus. That’s what we really hope for. ‘


– Dr. Stanley Perlman, University of Iowa

Not all people who get the virus develop antibodies, and some people end up with antibody levels that are not high enough to protect them.

It is also unclear how long the antibodies remain. COVID-19 antibodies decline after 60 days in most people, according to a CDC study of frontline healthcare workers in 12 states and another study from the same group in Nashville, Tennessee, though other studies, including one who examined healthcare workers in the UK, have indicated that IgG antibodies can last six months or more.

“Since it is not known how long immunity will be induced, we have the possibility that, as the virus continues to mutate, it will mutate to become a cold virus,” said Dr. Stanley Perlman, professor of microbiology and immunology at the University of Iowa. “That’s what we really hope for.”

If this were to happen, the virus could dim down until it simply turns into a bothersome but no longer deadly common cold. Common colds, which are coronaviruses that have not been eradicated, can provide immunity for up to three years. People who were infected with SARS or severe acute respiratory syndrome, also a coronavirus, had around three years of immunity.

“Sterilizing immunity” is a term used to explain a type of immunity that means that people cannot get a virus or the disease caused by a virus. That is most likely not the case with SARS-CoV-2. What experts, including Perlman, are now wondering is whether reinfections will cause less severe forms of the disease or will be asymptomatic.

“That could very well be what is happening to people who have a mild illness and are reinfected with a serious illness,” Perlman said. “I think the protection is much longer. So if someone comes out of an ICU and it’s normal, I think they will be protected for years. “

What we know about reinfection rates in the US

The federal government does not track reinfections, so the number of reinfection cases in the US is unknown.The CDC website page with information on reinfections was last updated on October 27.

Some states have shared details on probable or confirmed reinfections upon request.

California, for example, lists two confirmed reinfection cases out of the 3.3 million people who tested positive for the virus there, according to the state’s department of public health. About 615 people in Colorado meet the CDC criteria for reinfection, according to a state spokesperson. “This is a very small percentage of all cases,” representing 0.15% of all cases in Colorado, he said in an email. In Washington state, there are 716 suspected reinfections and one confirmed case.

The first documented case of reinfection in the United States occurred in a 25-year-old man in Reno, Nevada, according to a study published in the Lancet medical journal in October. The individual tested positive in April, had two negative tests in May, and then tested positive again in June.

His case was identified as part of a genomic sequencing program that had been established in Nevada during the pandemic. (The only way to confirm a reinfection is to sequence both samples to make sure they have different mutations, which occur naturally as the virus spreads from person to person.)

“If we look at the differences of the first sample compared to the original [virus from Wuhan, China] that they are absent from the second … that proves they were different, that they had diverged, before they could have entered that person, “said Richard Tillett, biostatistician at the Nevada Institute of Personalized Medicine and co-author of the Lancet Study.

What to know about reinfection and vaccines

If SARS-CoV-2 does not go away, reinfection could increase, even if the virus changes shape to become less deadly or cause less serious illness.

Vaccine developers such as Johnson & Johnson JNJ,
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and Moderna Inc. MRNA,
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They have said they are considering programs to develop COVID-19 boosters or vaccines to be given on a regular basis in the future.

“Over the next several years, we will receive a COVID-19 vaccine just like the flu vaccine,” J&J CEO Alex Gorsky told CNBC on February 9. “We can all imagine a future in which we live with this, but we can keep science at the same rate as the virus.”

As of now, the CDC says that people who have been infected once with the virus should get vaccinated, as long as they wait at least two months after a negative test.

The late-stage clinical trials for both licensed vaccines did not, for the most part, study the impact of the vaccines in people who had previously been infected with the virus. But Pfizer Inc. PFE,
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with the German partner BioNTech BNTX,
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and Moderna separately told the Food and Drug Administration during the regulatory review process that there is “limited” data suggesting that people who have had the virus may be at risk of reinfection and could benefit from vaccination.

“We’ve seen some case reports here and there of people getting reinfected,” Dr. Tal Zaks, Moderna’s chief medical officer, said in January during an investor call. “But in a context of millions of infected people, I don’t think it is material.”

Some healthcare workers at the Hackensack Meridian Health hospital system in New Jersey asked administrators if they should get vaccinated if they were already infected. The short answer is yes, according to Dr. Richard Varga, Hackensack’s chief medical officer.

“We are putting those people in the same PPE,” he said, “because you don’t know exactly how long and how effective their acquired immunity is.”

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