It is possible to catch Covid-19 twice, study shows

Aflurry of claims on social media sites have been of people saying they have gotten Covid-19 twice. Scientists have been sceptical about the possibility of that happening. After all, that’s what the immunity is supposed to be all about.

But researchers in Hong Kong have confirmed it – a person can be infected with Covid-19 twice.

The new proof comes from a 33-year-old man in Hong Kong who first caught COVID-19 in March.

He was tested for the coronavirus after he developed a cough, sore throat, fever, and a headache for 3 days. He stayed in the hospital until he twice tested negative for the virus in mid-April.

On Aug. 15, the man returned to Hong Kong from a recent trip to Spain and the U.K., areas that have recently seen a resurgence of COVID-19 cases.

At the airport, he was screened for COVID-19 using a test that checks saliva for the virus. He tested positive, but this time, had no symptoms. He was taken to the hospital for monitoring. His viral load -- the amount of virus he had in his body -- went down over time, suggesting that his immune system was taking care of the intrusion on its own.

The special thing about his case is that each time he was hospitalized, doctors sequenced the genome of the virus that infected him. It was slightly different from one infection to the next, suggesting that the virus had mutated -- or changed -- in the 4 months between his infections. It also proves that it’s possible for this coronavirus to infect the same person twice.

Experts with the World Health Organization responded to the case at a news briefing Monday.

“What we are learning about infection is that people do develop an immune response. What is not completely clear yet is how strong that immune response is and for how long that immune response lasts,” said Maria Van Kerkhove, PhD, an infectious disease epidemiologist with the World Health Organization in Geneva, Switzerland.

A study on the man’s case is being prepared for publication in the journal Clinical Infectious Diseases. Experts say the finding shouldn’t cause alarm, but it does have important implications for the development of herd immunity and efforts to come up with vaccines and treatments.

“This appears to be pretty clear-cut evidence of reinfection because of sequencing and isolation of two different viruses,” says Gregory Poland, MD, an expert on vaccine development and immunology at the Mayo Clinic in Rochester, MN.

“The big unknown is how often is this happening,” he says. More studies are needed to learn whether this was a rare case or something that is happening often.