The case of a man in the United States infected twice with COVID-19 shows there is much yet to learn about immune responses and also raises questions over vaccination, scientists said on Tuesday.
The 25-year old from Reno, Nevada, tested positive in April after showing mild symptoms, then got sick again in late May with a more serious bout, according to a case report in the Lancet Infectious Diseases medical journal.
“There are many reasons why a person might get sicker the second time around,” Akiko Iwasaki, a professor of immunobiology at Yale University, told NPR. “They may have been exposed to a lot higher levels of the virus the second time around,” she said.
The report was published just hours after US President Donald Trump, who was infected with COVID-19 and hospitalised earlier this month, said he believes he now has immunity and felt “so powerful”.
More than 37 million people have been reported to be infected by the novel coronavirus globally and 1,080,857 have died, according to a tally by Johns Hopkins University. In the United States, which leads the world in cases and deaths, more than 215,000 people have died.
Scientists said that while known incidences of reinfection appear rare – and the Nevada man has now recovered – cases like his were worrying. Other isolated cases of reinfection have been reported around the world, including in Asia and Europe.
A study of nearly 20,000 patients of the Mount Sinai Health System found stable levels of protective antibodies in people who had a mild case of COVID-19, making reinfection unlikely for at least three months.
“It is becoming increasingly clear that reinfections are possible, but we can’t yet know how common this will be,” said Simon Clarke, a microbiology expert at Britain’s Reading University.
“If people can be reinfected easily, it could also have implications for vaccination programmes as well as our understanding of when and how the pandemic will end.”
‘Still don’t know enough’
The Nevada patient’s doctors, who first reported the case in a non peer-reviewed paper in August, said sophisticated testing showed that the virus strains associated with each bout of infection were genetically different.
“These findings reinforce the point that we still do not know enough about the immune response to this infection,” said Paul Hunter, a professor in medicine at Britain’s University of East Anglia.
Brendan Wren, a professor of vaccinology at the London School of Hygiene and Tropical Medicine, said the Nevada case was the fifth confirmed example of reinfection worldwide.
“The demonstration that it is possible to be reinfected by SARS-CoV-2 may suggest that a COVID-19 vaccine may not be totally protective,” he said.
“However, given the (more than) 40 million cases worldwide, these small examples of reinfection are tiny and should not deter efforts to develop vaccines.”