Coronavirus spreading widely, though the amount of infectious persons may be lower than presumed

The recently ended stage in the coronavirus prevalence study conducted by the University of Tartu shows an even spread of the virus in all counties throughout Estonia. At the same time, it revealed that nearly half of the adults who gave a positive coronavirus test had coronavirus antibodies and are probably not contagious.

During the study stage from 11 to 22 February, participants gave a coronavirus (PCR) test and for the first time, also a blood test for detecting antibodies against the virus. According to head of the monitoring study, University of Tartu Professor of Family Medicine Ruth Kalda, researchers compared the information from the pre-test survey with the results of the PCR test and antibody analysis to estimate not only virus prevalence but also the proportion of people who have gained immunity to the virus.

In the course of the study stage, 2,647 randomly-selected adults gave a PCR test, and 2,531 of them also gave an antibody test. 53 people tested positive; 26 of them had had the disease, 27 were still contagious. This allows to conclude that although the estimated number of coronavirus-positive people in the adult population is 17,900, an average of 8,700 of them are infectious.

Antibodies from disease or vaccination

Antibodies against the coronavirus were found in 299 respondents. This means that an estimated 11% in the adult population, or about 120,800 people, have antibodies. Antibodies develop in people in the second or third week of infection or as a result of vaccination. The study revealed that most of the tested people had gained antibodies from a known (39%) or unknown (24%) illness. Nearly 36% of the tested persons had acquired antibodies from vaccination with one (8%) or two doses (28%).

Ruth Kalda admits that although the percentage of coronavirus infections in the adult population continues to be high, it can be assumed that the number of new infections identified solely based on the nasopharyngeal PCR test may have been overestimated so far. “Although data from the monitoring study cannot be directly transferred to the results of everyday tests made in the healthcare system, it still allows to conclude that a certain amount of these too are residual positive. This means that these people’s positive test result is due to quite a recent illness, but the individual is no longer a risk for others,” Kalda explained.

Restrictions observed ever more poorly

The behavioural survey conducted in the course of the monitoring study shows that as time goes on, people are increasingly less inclined to comply with the restrictions. Although masks are worn and hands are washed, conscious avoidance of meetings and keeping safe distance is gradually decreasing, particularly among younger adults. Participation in smaller events and visiting restaurants is growing both among younger adults and people aged 40–64. Nearly a third of those who have had a possible contact or close contact with an infected person change nothing in their behaviour after such contact.

Considering that nearly 60% of those who tested positive have no symptoms, non-compliance with the restrictions creates highly favourable conditions for the continued spread of the virus. What makes the situation even more serious: the monitoring study only reflects the infection figures of the adult population, while the Health Board data also refer to a large proportion of infections among school-aged children.

“Current restrictions must be taken seriously. Complying with all the rules is extremely important to protect risk groups and maintain the capacity of our hospital network. Until there is a growth in the number of people requiring hospital care, including intensive care, due to the coronavirus, and the number of vaccinated risk group members is low, it is inevitable to take all precautions that help curb the spread of the virus,” Kalda underlined.

The monitoring study is conducted by 17 researchers from five institutes of the University of Tartu. Synlab and Kantar Emor are involved as partners. More information can be found on the website of the coronavirus prevalence study.

Further information: Ruth Kalda, Head of Institute of Family Medicine and Public Health, Professor of Family Medicine, University of Tartu, +372 5698 5599,