Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said health officials were beginning to see “a number of cases” as reinfections this week.
“Well-documented cases,” he said, “of people who have been infected, after a relatively short period of time, measured from weeks to several months, return, expose themselves and become infected again.”
“So you really have to be careful not to be completely ̵
Although it is possible to be re-infected with the virus, there are still questions that scientists are working to answer, including who is more likely to be reinfected and how long antibodies protect people from another infection.
Scientists are studying how long antibodies last
Researchers at the University of Arizona have found that antibodies that protect against infection can persist for at least five to seven months after infection with Covid-19.
With a pandemic of less than a year, it will probably take some time before scientists can get a clear picture of immunity.
“However, we know that people infected with the first SARS coronavirus, which is the most similar virus to SARS-CoV-2, still see immunity 17 years after infection. “If SARS-CoV-2 is something like the first one, we expect the antibodies to last at least two years and it’s unlikely to be much shorter,” Deepta Bhattacharya, an immunobiologist at the University of Arizona School of Medicine, told CNN earlier.
Other studies, one from Massachusetts and the other from Canada, support the idea of long-term immunity.
It is unclear how the second infections may affect each Covid-19 vaccine. The Nevada man experienced more critical symptoms during his second infection, while the Hong Kong man had no obvious symptoms during his reinfection.
How severe the disease is can affect antibodies
There is something else that researchers have begun to notice: People who have a more severe attack of the disease tend to have a stronger immune response.
“There is a difference between asymptomatic people who have had a very mild infection, there seems to be a slightly higher number than those who do not have detectable antibodies,” said Swaminathan of the WHO. “But almost everyone who has moderate to severe disease has antibodies.”
Arizona’s Bhattacharya repeated this finding.
“People taken from the intensive care unit had higher levels of antibodies than people with a milder illness,” he said, adding that he still did not know what that would mean for long-term immunity.
CNN’s Maggie Fox contributed to this report.