Study Confirms It’s Possible to Catch COVID Twice

Aug 24, 2020 – Researchers in Hong Kong say they have confirmed that a person can be infected with COVID-19 twice.

There have been sporadic accounts on social media sites of people who say they have contracted COVID twice. But scientists have been skeptical of the possibility, saying there is no evidence that this is happening.

The new evidence comes from a 33-year-old man in Hong Kong who first contracted COVID-19 in March. He was tested for the coronavirus after developing a cough, sore throat, fever and headache for 3 days. He remained in the hospital until he tested twice negative for the virus in mid-April.

On August 15, the man returned to Hong Kong after a recent trip to Spain and the United Kingdom, areas that have recently seen a resurgence of COVID-19 cases. At the airport, he was tested for COVID-19 using a test that checks saliva for the virus. He tested positive, but this time he showed no symptoms. He was taken to the hospital for surveillance. His viral load – the amount of virus he had in his body – decreased over time, suggesting that his immune system was dealing with the intrusion on its own.

The peculiarity of his case is that each time he was hospitalized, the doctors sequenced the genome of the virus that had infected him. It was slightly different from infection to infection, suggesting the virus had mutated – or changed – within 4 months between its infections. It also proves that it is possible for this coronavirus to infect the same person twice.

Experts from the World Health Organization responded to the case at a press briefing on Monday.

“What we learn about infection is that people develop an immune response. What is not yet entirely clear is the strength of this immune response and the duration of this immune response, ”said Maria Van Kerkhove, PhD, epidemiologist of infectious diseases at the World Health Organization. in Geneva, Switzerland.

A study on the human case is being prepared for publication in the journal Clinical infectious diseases. Experts say the finding shouldn’t be alarming, but has important implications for the development of herd immunity and efforts to find vaccines and treatments.

“This appears to be fairly clear evidence of reinfection due to the sequencing and isolation of two different viruses,” says Gregory Poland, MD, expert in vaccine development and immunology at the Mayo Clinic in Rochester, MN. “The big unknown is how often this happens,” he says. More studies are needed to find out if this was a rare case or something that happens often.

Past experience guides present

Until we know more, Poland says the possibility of getting COVID-19 twice shouldn’t worry anyone.

This also happens with other types of coronavirus – those that cause the common cold. These coronaviruses change slightly each year as they travel around the globe, allowing them to continue to spread and cause their more mundane misery.

It also happens with the seasonal flu. This is the reason why people have to get the flu shot year after year, and why the flu shot has to change slightly every year in order to keep up with the ever changing flu virus.

“We’ve been making flu vaccines for 80 years, and clinical trials are underway as we speak to find new and better flu vaccines,” Poland says.

There has been other evidence that the virus that causes COVID-19 can change this way as well. Researchers at Howard Hughes Medical Center, Rockefeller University in New York, recently used a key part of the SARS-CoV-2 virus – the genetic instructions of its spike protein – to repeatedly infect human cells. Scientists have watched each new generation of viruses infect a new batch of cells. Over time, as it copied itself, some of the copies changed their genes to allow them to survive after scientists attacked them with neutralizing antibodies. These antibodies are one of the main weapons the immune system uses to recognize and deactivate a virus.

While this study is still a pre-print, meaning it has yet to be reviewed by outside experts, the authors wrote that their results suggest the virus may change in ways that help it escape. to our immune system. If that’s true, they wrote in mid-July, it means reinfection is possible, especially in people who have a weak immune response to the virus the first time they encounter it.

Good news

This appears to be true in the case of the Hong Kong man. When doctors tested his blood for antibodies to the virus, they found none. This could mean that he had a weak immune response to the virus the first time, or that the antibodies he produced when he was first infected worsened over time. But during his second infection, he quickly developed more antibodies, suggesting that the second infection acted a bit like a booster to activate his immune system. This is probably the reason why he had no symptoms the second time around.

This is good news, says Poland. This means that our bodies can fight the COVID-19 virus better, and catching it once means the second time may not be that bad.

But the fact that the virus can change quickly in this way has some impact on efforts to develop a vaccine that works well.

“I think a potential implication of this is that we will have to give booster doses. The question is how often, ”says Poland. This will depend on how fast the virus is growing and how often reinfection occurs in the real world.

“I’m a little surprised at 4 and a half months,” Poland says, referring to the time between infections from the Hong Kong man. “I’m not surprised by, you know, I got infected last winter and I got it again this winter,” he says.

It also suggests that immune therapies such as convalescent plasma and monoclonal antibodies may be of limited help over time, as the virus might change in ways that help it foil these treatments.

Convalescent plasma is basically a concentrated dose of antibodies from people who have recovered from COVID-19 infection. As the virus changes, the antibodies in this plasma may not work as well for future infections.

Pharmaceutical companies have learned to harness the power of monoclonal antibodies as powerful treatments for cancer and other diseases. Monoclonal antibodies, which are mass produced in a laboratory, mimic the body’s natural defenses against a pathogen. Just as the virus can become resistant to natural immunity, it can change in ways that help it defeat treatments created in the lab. Some pharmaceutical companies that are developing monoclonal antibodies to fight COVID-19 have already prepared for this possibility by making cocktails of antibodies designed to inactivate the virus by blocking it in different places, which can help prevent it from spreading. develop resistance to these therapies.

“We have a lot to learn,” says Poland. “Now that the proof of principle has been established, and I would say it is with this man, and with our knowledge of seasonal coronaviruses, we need to look more aggressively to define how often this happens.”


Clinical infectious diseases, August 24, 2020.

Gregory Poland, MD, consultant, Division of Pediatric Infectious Diseases; consultant, Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN.

Maria Van Kerkhove, PhD, Infectious Disease Epidemiologist, World Health Organization, Geneva, Switzerland.

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