Herd Immunity is not realistic
For the first time we have true randomized testing –and it shows that Austria was officially picking up about a quarter of the real number of infections in the population. So when Austria was officially saying 7,000 were infected, the true number was 28,500. Finally, this puts a solid limit on the chance that asymptomatic rate of infection was high. There is no iceberg.
About 75% of cases were mild or truly asymptomatic (and thus not getting officially tested), but it was still only a small slice of the population — just one third of one percent.
Peter Beaumont, The Guardian
The co-founder of Sora, Christoph Hofinger, told a news conference: “Based on this study, we believe that 0.33% of the population in Austria was acutely infected in early April.” Given the margin of error, the figure was 95% likely to be between 0.12% and 0.76%.
99% of the population is still vulnerable
The Austrian chancellor estimates only 1% of the population had had the infection (presumably he is including an estimate of people who had already had the virus, cleared it, and tested negative).
The Austrian chancellor, Sebastian Kurz, who saw initial findings a few days ago, said on Monday that the rate of infection was around 1%. This disproved the idea of herd immunity, which requires widespread infection, as a viable policy option, he said.
Austria has sampled 1,554 people with help from a polling company from April 1 – 6. The nose and throat swabs they used will have found active infections, not past ones. But the peak of infections was March 26, so this will still have included some, perhaps many, of those people who were infected the week before. It depends on how long people shed virus for, and like everything with this virus, that’s not simple. Some people shed for a long time even weeks, but others don’t.
Ten times worse than the flu
Austria has officially recorded 6,941 cases in total of which 337 have died. So the mortality rate for diagnosed cases is 5% and likely to rise due to the lag of one to two weeks (and even longer) before deaths occur. So the mortality rate of all infections (including asymptomatic) is more like 1.2%, making this at least ten times deadlier than the flu. (It may be worse if Austria was able to protect the 80+ and other vulnerable groups).
Hopefully new treatments will improve that.
We can see that testing around 1 – 6th April should give a realistic estimate of the scale of infections. Nose and throat swabs are probably a PCR test looking for two RNA segments unique to the virus. PCR means Polymerase Chain Reaction, where small amounts of DNA or RNA get amplified up so they can be tested.
Austria was among the early movers in Europe to try to contain the outbreak, clamping down on public life and enforcing social distancing when cases were still in the hundreds and few had died. The country will start to relax some of the measures next week, when small shops and hardware and gardening stores can reopen, but it will keep schools and other stores closed until May.
The only way to figure out the true rate of asymptomatic infections is with an antibody test (also known as a serum test), but that’s not possible yet, though many labs are reportedly close. These tests require a blood sample, but will hopefully show how many people were exposed to the virus, at least for a few months after the infection.