Number of infectious adults has grown almost four times in a month

The results of the prevalence study led by the University of Tartu show that the number of people with coronavirus infection has surged compared to December. Most of the infected persons have no symptoms, however, and carry the virus unknowingly. The percentage of adults with antibodies is increasing slowly, having risen only by 1 per cent over the last month.

During the study conducted from 11 to 24 January, 2,352 random-sampled* adult people were tested. 3.3% of them, i.e. on average, one in 31 people, tested positive. Two thirds of the infected (on average, 2.1% of the tested people) were infectious. This is almost four times more than in December. A third of the people who tested positive this time had recently recovered from the disease and did not pose a risk of infection to others. Their test result was regarded as residual positive.

According to the head of the survey, the University of Tartu Professor of Family Medicine Ruth Kalda, most of the infected people are currently from the younger age group (aged 18–39), where one person in every 23 is estimated to be infected. Among people aged over 65, there are half as many infected.

Booster dose is the surest way to prevent infection

During this wave of the survey, the percentage of infected people was revealed to be the highest ever during the pandemic. According to Kalda, this creates favourable conditions for the continuing spread of the virus, because people transmit the virus unknowingly.

During this wave of the survey, the percentage of infected people was revealed to be the highest ever during the pandemic. According to Kalda, this creates favourable conditions for the continuing spread of the virus, because people transmit the virus unknowingly.

“The booster dose of the vaccine is the surest way to slow down the spread of the virus. We can see from the results of this wave that people get infected repeatedly, even after a completed vaccination series. It is estimated that one in eighteen adult people who have been vaccinated with two doses are infected, and one in forty among those who have got the booster dose. The third dose reduces the infection risk more than twice,” said Kalda.

Regardless of the rapid spread of the virus, the proportion of people with antibodies has increased by only 1% over the last month, reaching close to 83% of the adult population. Kalda attributes this to the fact that while there have been a lot of third vaccine injections recently, the number of first-dose vaccinations has remained rather modest. “The fact that antibody prevalence in the older age group is about 90% and also the infection rate is the lowest in that group, gives hope that it may be possible to mitigate the risk of hospital overload,” she said.

Risk behaviour remains unchanged

Last month also saw an increase in the percentage of people who had been in contact with the infected. In December, one in 17 adults had been in contact with a virus carrier, now the ratio was one in 13. At the same time, almost 70% of those who have been in contact do not change anything in their behaviour after the contact. This finding is similar to that of the previous month.

Kalda said that the current spread of the virus, the proportion of asymptomatic cases, people’s risk behaviour, as well as the virus situation in other European countries show that this Covid-19 wave has not peaked yet.

The prevalence study is carried out by a broad-based research group of the University of Tartu in cooperation with Synlab, Medicum and Kantar Emor. The study continues this year to provide the scientific advisory board and the government with evidence-based data about the prevalence of the infection. The principal investigator of the study, University of Tartu Professor of Public Health Mikk Jürisson says that the strength of this survey is the large, population-based random sample. “The survey also detects infected people with no symptoms who may be passing on the infection unknowingly. These data are necessary for both choosing the best measures and forecasting the course of the disease,” Jürisson explained.

For more information about the coronavirus prevalence study, see the University of Tartu website.

The study is funded by the European Regional Development Fund from the EU measure to respond to the Covid-19 pandemic.

* The sample has been stratified by region, age group, gender and education level, which means that the weighted averages are used, not the simple arithmetic mean, to estimate the prevalence.

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