“This is really good news to see that we are seeing sustained levels of immune response in humans so far,” Mike Ryan, WHO’s top emergency expert, told a news conference. “It also gives us hope on the vaccine side.”
Maria van Kerkhove, WHO’s technical lead on COVID-19, said: “We still need to follow these individuals for a longer period of time to see how long immunity lasts.”
Isolated cases of re-infection with COVID-19, the disease caused by the SARS-CoV-2 virus, had raised concerns that immunity might be short-lived and that recovered patients may swiftly fall sick again.
But the results of this recent study, carried out in a cohort of UK healthcare workers – who are among those at highest risk of contracting COVID-19 – suggest cases of reinfection are likely to remain extremely rare.
“Being infected with COVID-19 does offer protection against re-infection for most people for at least six months,” Eyre said. “We found no new symptomatic infections in any of the participants who had tested positive for antibodies.”
The study, part of a major staff testing programme, covered a 30-week period between April and November 2020. Its results have not peer-reviewed by other scientists but were published before review on the MedRxiv website.
During the study, 89 of 11,052 staff without antibodies developed a new infection with symptoms, while none of the 1,246 staff with antibodies developed a symptomatic infection.
Staff with antibodies were also less likely to test positive for COVID-19 without symptoms, the researchers said, with 76 without antibodies testing positive, compared to only three with antibodies. Those three were all well and did not develop COVID-19 symptoms, they added.