First covid-19 reinfection documented in Hong Kong, researchers say

The case has potential implications for vaccine development, as well as policies based around the concept of herd immunity that presume those who recover from the virus are not likely to be reinfected. But some experts noted that it was also in line with what immunologists would expect.

“[T]his is a textbook example of how immunity should work,” Akiko Iwasaki, an immunology expert at Yale University, tweeted on Monday.

The 33-year-old man, an unnamed IT worker from the city, was first hospitalized in late March after testing positive for covid-19. His symptoms included a fever and a cough.

The man was released from hospital in mid-April after testing negative for the virus and having no further symptoms. But after visiting Spain in August, he tested positive again upon returning to Hong Kong, despite appearing asymptomatic.

Physicians at first thought he might be a persistent carrier of the virus, the study’s authors write, but they sequenced the genome of his first and second infection to show the virus strain was different, indicating he had been reinfected.

If the man’s reinfection is confirmed, it may suggest that the level of immunity after an infection may be lower than many had hoped or it could simply indicate that immunity occurs on a spectrum and while the man had no signs of illness — likely a sign of partial immune protection — he did test positive.

“Many believe that recovered Covid-19 patients have immunity against re-infection because most developed a serum neutralizing antibody response,” a news release announcing the study noted. “However, there is evidence that some patients have waning antibody level after a few months.”

Kwok-Yung Hyuen and other study authors suggested in their paper that their “results suggest SARS-CoV-2 may continue to circulate among humans despite herd immunity,” using the technical name of the novel coronavirus.

The study’s authors conclude that herd immunity is unlikely to eliminate covid-19 on its own and that a potential covid-19 vaccine may not provide lifelong immunity to the disease.

They also recommend that even those who have recovered from the coronavirus should continue to comply with social distancing rules and other measures such as wearing a mask.

Iwasaki, the Yale expert, said that study’s findings were “no cause for alarm,” noting that the second infection was asymptomatic implying that while immunity was not enough to block reinfection, it protected the person from disease.

The paper also found that the patient who had no detectable antibodies at the time of the second infection he developed antibodies afterward, Iwasaki wrote on Twitter. “This is encouraging,” she said.

Studies that look at antibodies after a covid-19 infection have reached differing conclusions about the level of immunity that can be expected months later. Experts have noted with the common cold, another illness caused by a coronavirus, people are often reinfected each season.

What may be important is understanding how widespread reinfection is and whether subsequent infections carry as many risks as the first infection, researchers say.

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