Paris – The first study to investigate the case of a person in the U.S. who contracted COVID-19 twice found reinfection can occur swiftly and the second bout of illness can be more severe.
The research, published in the Lancet medical journal, indicates that exposure to the virus may not guarantee future immunity.
The study examined the case of a 25-year-old man living in Nevada who became infected with two different genetic variants of the SARS-CoV-2 virus in less than two months. He tested negative twice in between, meaning he’s unlikely to have suffered a single prolonged infection.
The findings come as U.S. President Donald Trump says he’s immune to the virus after a single encounter. Any new findings on resistance can also have implications for a vaccine as drugmakers race toward the finish line.
The degree of protective immunity after a COVID-19 infection is one of the pandemic’s great unknowns.
So far five cases of reinfection have been recorded since the start of the outbreak late last year. The paper noted four other cases of reinfection confirmed globally, with one patient each in Belgium, the Netherlands, Hong Kong and Ecuador. Only the patient in Ecuador also suffered a worse bout of illness the second time around. It’s also possible people with no symptoms could be infected multiple times without knowing it.
The Nevada man first tested positive for the virus mid-April after experiencing a headache, coughing, nausea and diarrhea. He had no underlying conditions that could’ve worsened his illness. He isolated and got better by the end of the month.
At the end of May, though, the man consulted at an urgent care center with fever and dizziness in addition to the symptoms he had experienced the prior month. Five days later he was hospitalized with shortness of breath and given oxygen before testing positive for COVID-19 once more.
Scientists sequenced the genomes of the patient’s virus samples and found significant differences, suggesting the man was infected by two distinct versions of the coronavirus.
The researchers said they couldn’t be sure why the second infection was worse. It’s possible the patient was exposed to a higher dose of virus the second time, that the version he encountered was more virulent or even that the presence of antibodies from the first infection was to blame in a twist observed with another coronavirus. It’s even possible — but unlikely — that there was a continuous infection with some sort of deactivation-reactivation dynamic, they wrote.
"There are still many unknowns,” said Mark Pandori, director of the Nevada State Public Health Laboratory and lead author of the study. "Our findings signal that a previous SARS-CoV-2 infection may not necessarily protect against future infection. The possibility of reinfections could have significant implications for our understanding of COVID-19 immunity, especially in the absence of an effective vaccine.”
Vaccines work by triggering the body's natural immune response to a certain pathogen, arming it with antibodies it to fight off future waves of infection.
But it is not at all clear how long COVID-19 antibodies last.
For some diseases, such as measles, infection confers lifelong immunity. For other pathogens, immunity may be fleeting at best.
In a linked comment to The Lancet paper, Akiko Iwasaka, a professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale University, said the findings could impact public health measures.
"As more cases of reinfection surface, the scientific community will have the opportunity to understand better the correlates of protection and how frequently natural infections with SARS-CoV-2 induce that level of immunity," she said.
"This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity," added Iwasaka, who was not involved in the study.