Published: August 5, 2020
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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 above).
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.
(Earlier reports that Bergamo allegedly had 57% antibody prevalence were likely based on hospitalized patients or severe cases and were not representative for the whole population.)
27% of people with antibodies remained asymptomatic, 23% had 1-2 (mild) symptoms, and 41% had 3 or more 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 smell or taste – 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. Instead, many people neutralize the virus with pre-existing or new T-cells or with mucosal (IgA) antibodies, as first shown by a Swiss immunological study.
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, most other regions of Italy are still far from such levels and thus remain vulnerable to the new coronavirus. The same is true for places like Germany with only 1.3% IgG prevalence.
Instead of permanently or repeatedly locking down their societies while waiting for an uncertain vaccine, these and many other places should urgently consider an early treatment strategy for the high-risk segment of their population and study the Swedish approach to pandemic management.
More: Results of the Italian antibody seroprevalence study (ISTAT, August 3, 2020)
Related: Covid-19: A Report from Italy (March 2020)