One optimistic theory has been that many tens of millions of people have already been infected with coronavirus so the Case Fatality Rate is actually quite low and we are heading toward Herd Immunity. Unfortunately, due to the testing shortage, we’ve been lacking tests performed on a large fraction of people. But here’s a valuable new sample: 1/3rd of population of Robbio in Italy have had their blood tested for CV antibodies just in the last few days. From FranceTVInfo:

Italy: large-scale serological tests Italy is the first country in Europe to use large-scale serological testing. In a blood test, it is possible to know if the body has reacted to the virus. Updated 04/06/2020 | 17:29 A blood test is enough to tell if someone has had the Covid-19 coronavirus , and whether or not they can get out of the house and go to work again. This is one of the major challenges of the coming weeks in Italy, and what probably awaits us in France. These serological tests are a first in Europe and an educational test. 2,000 residents of the town of Robbio (Italy) accepted a blood test to find out if they had developed antibodies to Covid-19.

Robbio is a town about 50 kilometers southwest of Milan, so it’s in the hot zone, but perhaps not in hottest zone, which I believe is northeast of Milan in Bergamo. The total population is about 6,000, so they tested about 1/3rd of the town in a couple of days earlier this month.

13 to 14% of people immunized A third of the city was tested in 48 hours. Local health professionals welcome this. A blood test is the only way to know for sure whether the body has reacted to the virus and whether some immunity has been acquired. In Italy, the test is paid, 45 euros, and is not reimbursed. Finally, it is done on a voluntary basis. Immunized citizens are not in the majority, according to the first results, and represent 13 to 14% of the sample analyzed.

Can anybody find out the number of excess deaths in small town of Robbio in Lombardy, where 2000 of 6000 residents have been tested for CV antibodies, with 14% positive? This would give us a better Case Fatality Rate estimate.

Update: From Agenzia Italia on April 2 via Google Translate:

At the moment, there are 27 positive people in Robbio and there are 4 dead, “but the figures are falling, many have died from the virus without affecting its positivity.

I think that means the mayor believes that both the confirmed cases (before his new testing initiative) and death counts are understated. Many small town mayors in Lombardy have made the same point that they have had many more excess deaths (relative to March of previous) years than were enumerated in their town’s CV death toll. (Of course, some of the excess deaths could be due to patients avoiding hospitals due to infection fears or overcrowding, and then dying of lack of care for something else.)

In the past two days, the ATS has called us asking for the name of two citizens they did not find from whom they had been contacted previously. I replied that they had already been buried for days.”

Other mayors have argued that their death tolls were understated because the authorities were only counting CV deaths in hospitals.

So with a population of 6,169, Robbio had 27 confirmed cases, but blood tests of 2000 residents found 13-14% positive for antibodies, suggesting that confirmed cases were only about 3% of actual cases.

Another update: An April 1 report in 24 Ore says that there were 6 deaths in Robbio in March 2020 compared to an average of 4.6 in March 2015-2019. So Robbio was likely not one of the worst hit towns in northern Italy. For example, in Bergamo (about 100 km to the northeast), for example, there were 430 deaths in March 2020 versus a mean of 109.8 in the previous five years.

So if 13.5% of Robbio’s 6,169 people were infected, that would be 832 infections. If all six deaths in March were due to the virus that would be an Infection Fatality Rate of 6/832 or 0.7% (so far — as we’ve seen with the Diamond Princess, deaths keep going up over the weeks). My impression is that Robbio’s province of Pavia didn’t have the overwhelming run on the hospitals as in Bergamo. Plus Pavia is a real center of medicine in Italy. So a 0.7% IFR is under fairly good circumstances, whereas Bergamo shows how bad it can get when the hospitals get overrun.