The Italian health and statistics authorities ISS and ISTAT have published the results of their first nationwide coronavirus antibody study based on close to 65,000 participants.
The study found a nationwide IgG antibody prevalence of 2.5%. The highest prevalence was found in the northern region of Lombardy (7.5%), the lowest prevalence was found in the southern region of Sicily (0.3%). (See chart below).
In the former coronavirus hotspot provinces of Bergamo and Cremona (both within Lombardy region), IgG antibody prevalence was 24% and 19%, matching other global hotspots like New York and once again confirming a ~20% IgG antibody prevalence threshold.
27% of seropositive people (people who had antibodies) remained asymptomatic, 23% had 1-2 (mild) symptoms, and 41% had 3+ symptoms or a temporary loss of the sense of smell or taste.
Importantly, only 25% to 27% of people who reported a temporary loss of the sense of taste or smell – a very typical Covid-19 symptom – had IgG antibodies.
This confirms the results of the previous Spanish antibody study and once again shows that only a fraction of the people who likely had contact with the new coronavirus (need to) develop IgG antibodies to neutralize the virus. Many people appear to neutralize the virus with pre-existing or new T-cells or with mucosal (IgA) antibodies, as first shown by a Swiss immunological study.
In turn, this means that even in former hotspots like Bergamo – which pioneered the fatal strategy of moving Covid patients into nursing homes, a mistake later copied by places like New York and New Jersey – the population-adjusted Covid lethality (IFR) is likely close to 0.1%, as 80% or more of the population may already have come into contact with the new coronavirus.
However, Bergamo was caught off guard by the very rapid pre-symptomatic spread of the virus and subsequently suffered a collapse of its elderly care and health care system and an extremely high mortality during several weeks in March, leading to the notorious television images.
While places like Bergamo and Cremona likely reached the much-cited “herd immunity” threshold,