text: SAY you have caught covid-19 and recovered – are you now immune for life, or could you catch it again? We just don’t know yet.
  In February, reports emerged of a woman in Japan who had been given the all-clear after having covid-19 but then tested positive for the SARS-CoV-2 virus a second time. There have also been reports of a man in Japan testing positive after being given the all-clear, and anecdotal cases of second positives have emerged from China, too.
  This has raised fears that people may not develop immunity to the virus. This would mean that, until we have an effective vaccine, we could all experience repeated rounds of infection.
  But the science is still uncertain. “There is some anecdotal evidence of reinfections, but we really don’t know,” says Ira Longini at the University of Florida. It may be that the tests used were unreliable, which is a problem with tests for other respiratory viruses, says Jeffrey Shaman at Columbia University in New York.
  Early signs from small animal experiments are reassuring. A team from the Chinese Academy of Medical Sciences in Beijing exposed four rhesus macaques to the virus. A week later, all four were ill with covid-19-like symptoms and had high virus loads. Two weeks later, the macaques had recovered and were confirmed to have antibodies to the virus in their bloodstream.
  “You can be infected with other coronaviruses over and over. We don’t know if that’s true for this virus”
  The researchers then tried to reinfect two of them but failed, which suggests the animals were immune (bioRxiv, doi.org/ggn8r8). “That finding is very encouraging, as it suggests that it is possible to induce protective immunity against the virus,” says Alfredo Garzino-Demo at the University of Maryland School of Medicine.
  But that doesn’t necessarily mean long-term immunity. There are other coronaviruses circulating among humans and although they induce immunity, this doesn’t last. “Some other viruses in the coronavirus family, such as those that cause common colds, tend to induce immunity that is relatively short-lived, at around three months,” says Peter Openshaw at Imperial College London.
  “Because [the virus] is so new, we do not yet know how long any protection generated through infection will last. We urgently need more research looking at the immune responses of people who have recovered from infection to be sure,” says Openshaw.
  Other immunologists agree. “Immunity to SARS-CoV-2 is not yet well understood and we do not know how protective the antibody response will be in the long-term,” says Erica Bickerton at the Pirbright Institute in the UK.
  “For ordinary coronavirus infections, you do not get lasting immunity,” says Longini. “You can be infected over and over, and we really don’t know for this novel coronavirus if that’s also true.”
  Other infectious disease specialists are more optimistic. “The evidence is increasingly convincing that infection with SARS-CoV-2 leads to an antibody response that is protective. Most likely this protection is for life,” says Martin Hibberd at the London School of Hygiene & Tropical Medicine. “Although we need more evidence to be sure of this, people who have recovered are unlikely to be infected with SARS-CoV-2 again.”
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