Less than 1% of the Austrian population is “acutely infected” with coronavirus, new research based on testing a representative sample of more than 1,500 people suggests.
The government-commissioned study, reportedly the first of its kind in continental Europe, was led by the polling company Sora, which is known for projecting election results, in cooperation with the Red Cross, the Medical University of Vienna, and other institutions.
The study made it possible to estimate the prevalence of acute coronavirus infections in Austria among those not in hospital at the beginning of April, and was designed to provide a clearer picture of the total number of infections, given gaps in testing.
The research, if replicated and confirmed elsewhere, would appear to scotch hopes of countries being remotely close to relying on “herd immunity” – where enough of the population is exposed to the virus to build up a combined immunity – as a viable policy option.
The study stands in contrast to controversial modelling by researchers at Oxford University who, in one scenario they examined, suggested most people in the UK might already have been infected with Covid-19.
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%.
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.
However, researchers, speaking at a press conference to release the results, said the study provided only a “snapshot” and did not account for asymptomatic infections, or people who were immune.
“We did not find out how many people are immune, but only how many people in Austria are currently acutely infected,” said Günther Ogris, from Sora.
The issue of the proportion of asymptomatic infections in the population remains highly contested, with a World Health Organization report in February suggesting truly asymptomatic cases were relatively rare. However, another small Chinese study, reported in the British Medical Journal earlier this month, posited that up to four-fifths of all infections could be without symptoms.
Ogris said Sora had “defined the population as all people living in Austria”, and added that the youngest test subject was not yet a year old, and the oldest was aged 94.
Commenting on the result, the science minister, Heinz Fassmann, said it indicated a low rate of immunity, which meant that without controls there was a continued risk of an exponential growth in infections.
“The mountain is higher than expected and we are not yet on the safe side,” he said.
Austria’s current policy is to test people with symptoms, especially if they have been to a known hotspot or in close contact with an infected individual. That means many people, such as those with no symptoms, or no known contact to an at-risk area, go undetected.
The country reacted early to the outbreak, closing schools, restaurants, theatres and other gathering places more than three weeks ago, and telling people to stay home.
Hospital admissions have stabilised, with the daily percentage increase in infections in low single digits. There have been 319 deaths and 13,337 confirmed cases, of which about 7,000 people are still infected. The study estimated the current number of infections was more than four times that, however, at around 28,500 people. It excluded those in hospital, currently about 1,000 people.
The study, conducted from 1-6 April, tested 1,554 people. It did not involve antibody tests, which can tell whether a person was previously infected and is therefore probably immune. Future studies should involve antibody tests, the government has said, to inform policy as the country starts to reopen shops from 14 April.
The education minister, Heinz Fassmann, whose portfolio includes research, said: “We must monitor whether there is a second wave and the number of infected people starts to rise again. We are still in a very, very sensitive situation. This study shows that, too. Corona is in our society.”