Booster dose greatly reduces the risk of infection

Results of the most recent wave of the coronavirus prevalence study led by the University of Tartu indicate that the booster dose of the vaccine can reduce the risk of coronavirus infection several times. Compared to October, the number of adults with coronavirus antibodies has increased significantly. The proportion of virus carriers has fallen by a third within a month.

During the study wave from 1 to 13 December, 2,331 adults across Estonia were tested for coronavirus. 35 people tested positive, but as 22 of them had just recovered from the virus, only 13 were still infectious. This means that, on average, every 175th adult, or 0.6% of the adult population, can currently be infectious in Estonia, down by nearly a third compared to the study wave conducted in October.

The results indicated that those who have already received the booster dose are best protected against the virus. Their risk of infection is nearly ten times lower than that of unvaccinated people and nearly five times lower than that of people vaccinated with two doses.

Coronavirus antibody levels were determined in 2,290 participants, 2,130 of whom have antibodies. Thus, an estimated 82% of adults have developed antibodies — which is 5% more than in October. The situation is the best among older people, as their antibody prevalence has risen to 91%.

The leader of the prevalence study, Professor of Family Medicine of the University of Tartu Ruth Kalda said the study results seem to be rather encouraging before the coming holidays, but the situation can change quickly. "Seeing how the infection rates have started to rise again in several European countries, the current situation should be taken as a momentary reprieve before the new wave due to the Omicron strain. Our results show a rather good antibody prevalence, but we do not know how well the antibodies can protect us from the new virus strain. International studies to date, mainly based on lab experiments, have shown that the Omicron strain can break through this protection but less often leads to a serious disease. To mitigate the risks, it would therefore be wise to get vaccinated and also get the booster dose as soon as possible, as this provides significantly better protection against a serious illness," Kalda explained.

Third wave of the virus made people more cautious

The behavioural analysis of the prevalence study revealed that risk behaviour has decreased. For example, masks are worn more carefully than before, distance working is more common, and physical meetings are replaced by electronic ones more often. At the same time, almost three quarters of those who have been in contact with a virus carrier do nothing to prevent the spread of the infection. Still, unvaccinated people have become more cautious, and half of them remain in at least partial self-isolation after close contact.

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.

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

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

Further information: Ruth Kalda, Head of the Institute of Family Medicine and Public Health, Professor of Family Medicine, 5698 5599,


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