Antibody study shows one in thirty Slovenians exposed to coronavirus

Among 1,368 persons tested, 41 or 3.1% had antibodies in their blood samples and two tested positive for Covid-19, according to Mario Poljak, a researcher at the Institute of Microbiology and Immunology, which led the study.

Given that the sample was representative of the entire population, researchers can say with 95% certainty that 2-4% of the population had had an immune response to Covid-19.

But Miroslav Petrovec, the head of the Institute of Microbiology and Immunology, cautioned that this did not necessarily mean those people are immune to Covid-19, nor how durable their immunity may be.

A back-of-the-envelope calculation based on the figures would appear to indicate that the Covid-19 death rate is low, around the same as for the seasonal influenza, but the authors of the study warned that this cannot be concluded from the study.

As Petrovec noted, the study was designed to gauge the population's immune response, not to measure the death rate. As such, it can only provide answers to questions that it set out to answer.

Poljak noted that the implicit death rate in Slovenia is around the same level as in comparable European countries, but he said benchmarking was made difficult by differences in how individual countries record causes of death.

While similar studies have been conducted in other countries, Poljak said this was the first study in the world to measure the immunity of a representative sample of the population and the first to test for both Covid-19 (with nasal swabs) and immune response (blood sample).

What is more, the participants will be remotely monitored every two weeks for six months and tested again at the end of October, which will give public health authorities crucial data before a possible second wave of the epidemic.

Some countries, including France and the US, have discovered based on a re-examination of old swab samples that they had had coronavirus cases significantly before the first cases were confirmed.

Asked whether that may be the case in Slovenia, Poljak said that this was indeed possible. The institute stores samples for a long time and could theoretically go back and re-test some of the samples.

The researchers warned, however, that such a study would not be representative since samples are usually taken only from patients with particularly severe forms of a disease.

Slovenia's official coronavirus case count rose by three to 1,448 by Tuesday and 99 deaths were reported.