An Italian study published Friday in the Monthly Medical Journal revealed that the natural immunity developed after the first infection with COVID-19 will reduce the risk of reinfection for at least a year. Gamma Internal Medicine.
Of a group of 1,579 patients who tested positive, only 5 cases of re-infection were observed. The mean interval between initial infection and re-infection was more than 230 days.
Of the 13,496 people without initially infected with SARS-CoV-2, 528 had a primary infection. The infection rate per 100,000 people was 1 for re-infection versus 15.1 for new infections. “These differences are significant,” notes the medical doctor at NYC Health + Hospitals Study author Mitchell Katz.
The study concluded that natural immunity to COVID-19 appears to confer a protective effect for at least a year, which is comparable to the protection reported in recent vaccine studies.
A team of scientists has followed groups of patients from the Lombardy region, one of the hardest-hit health regions in Italy. Asymptomatic and asymptomatic patients of all ages recruited from several screening programs were included.
“We studied the occurrence of primary infection and re-infection of SARS-CoV-2 in people diagnosed with the virus during the first wave of the epidemic in Italy.” – Stady
Reinfection is considered “valid” if a second positive PCR is found 90 days after the first infection has completely resolved and with at least two consecutive negative tests between episodes. “This 90-day window was chosen taking into account the persistence of the RNA virus for up to 12 weeks.”
However, the author of the study states that the observation ended before SARS-CoV-2 variants began to spread.
“Before assuming that people with SARS-CoV-2 infection are protected from future infections, there are two caveats. We don’t know how long natural immunity will last. We don’t know if natural immunity also provides protection for the SARS-CoV-2 variant,” notes Doctor Mitchell. Katz.
These results complement those of an American study, which found that patients who tested positive for SARS-CoV-2 antibodies were less likely to develop COVID-19 infection in 90 days than patients who had no antibodies.