People who have had a coronavirus infection once are protected from a second infection for at least nine months and possibly longer, a new study suggests.
Long-term care facility residents who tested positive for Covid-19 antibodies had an 85% reduced risk of reinfection, and staff had a 60% lower risk, according to the study published on Thursday in the journal Lancet Healthy Longevity.
A team at University College London and other UK-based institutions analyzed data on 682 residents and 1,429 staff members from long-term care facilities in England between October and February. Some of the residents and staff were thought to have had Covid-19 in the past because they tested positive for antibodies in blood samples collected between June and November.
Among residents who tested negative for antibodies, the researchers found that 93 out of 456 — or 20% — later tested positive for Covid-19 infections during the study. But just 2% of residents who tested positive for antibodies later tested positive for Covid-19.
Among staff members who tested negative for antibodies, the researchers found 11% later acquired Covid-19 infections during the study. Among staff who tested positive for antibodies, only 2% did.
"… the risk of PCR-positive SARS-CoV-2 infection was substantially lower in residents and staff who were positive for SARS-CoV-2- specific antibodies at baseline," the researchers wrote in their study. SARS-CoV-2 is the name of the coronavirus that causes Covid-19.
"Our findings suggest that previous infection reduced the risk of reinfection by approximately 85% in residents and 60% in staff members. We identified only 14 cases of possible reinfection, mainly affecting staff, and although almost all of these individuals reported symptoms, none required hospital treatment," they wrote. "These findings suggests that previous SARS-CoV-2 infection provides a high degree of protection against a second infection and is broadly consistent with findings from longitudinal studies in hospital staff."
"It's really good news that natural infection protects against reinfection in this time period. The risk of being infected twice appears to be very low,” Dr. Maria Krutikov of the University College London Institute of Health Informatics said in a statement.
More research is needed to determine whether similar findings would emerge among a larger group of people from other regions of the world.