Protection Against Reinfection in Lombardy, Italy
How many patients who had Covid-19 infection during the first wave of the virus in Lombardy, Italy had it again, at least 90 days and 2 negative RT-PCR tests, later? There is a new study from Lombardy that demonstrates that very few of the original cohort of Covid-19 + patients (Feb-July 2020) redeveloped Covid-19 during the next year. Patients who were negative during those early months were followed for almost a year for comparison, and many developed Covid-19. The difference in the number of infections in these two groups was statistically significant (P<0.001).
Reinfection was defined as a positive RT-PCR Covid test more than 90 days after recovery plus 2 negative tests. Only 5 patients of 1579 original Covid + patients had a reinfection - and one was hospitalized.
There were 528 Covid-19 infections in the original 12,968 Covid-19 negative subjects while being observed for almost a year.
Antibody levels and other markers of immunity were not measured, but the statistical difference in infection rate was a strong indicator that the previously infected patients had enough natural acquired immunity from their first infection to prevent reinfection for almost a year. (JAMA Internal Medicine May 28, 2021) Recent studies demonstrate that there is a robust antibody response in patients who had Covid-19 after just 1 dose of vaccine.