The PROSECO prospective study shows the dynamics of anti-SARS-CoV-2 antibodies in the Czech population

18 Aug 2021

The PROSECO prospective study by RECETOX - Masaryk University shows the dynamics of anti-SARS-CoV-2 antibodies in the Czech population until March 2021

Scientists from Masaryk University's RECETOX research center have published data from the first large-scale population-based study on the presence of COVID-19 antibodies in the Czech population.

The data, analyzed from PCR testing, revealed that almost 1.7 million people in the Czech Republic had contracted the virus since the epidemic began; this constitutes about 17% of the population. However, this number does not account for asymptomatic or mild infections, which were not confirmed by testing.

While in the first pandemic wave, only 87 new cases were confirmed per 100,000 inhabitants during three months, at the peak of the second wave, more than 100 new cases per 100,000 people were confirmed daily, ranking the Czech Republic amongst the worst-hit countries in Europe and the world. Nevertheless, the actual number of people who were infected and developed antibodies during the second wave of the pandemic can only be estimated by a national seroprevalence study, in which a representative sample of the population is tested for the presence of anti-SARS-CoV-2 antibodies. Several published studies have described the progression of COVID-19 infection during the second wave of the pandemic, but as of yet, none has covered the hard-hit Central and Eastern European region.

This week, RECETOX scientists published results from the first phase of PROSECO, a long-term prospective study monitoring the dynamics of anti-SARS-CoV-2 antibody levels in the Czech population. The study was made possible by the Czech Ministry of Interior health insurance company’s prevention fund, which has supported repeated measurements of anti-SARS-CoV-2 antibodies in the blood of volunteer clients. The three-phase study started in October 2020 and completed recruiting participants by March 2021 before initiating the extensive national vaccination campaign. Over 30,000 participants, 18 years and older, provided blood samples collected by the QualityLab's network of accredited laboratories. Then, the antibody levels were measured to determine the dynamics of IgG antibody seroconversion to SARS-CoV-2 in the immunologically naive and unvaccinated population.

In addition to RECETOX staff, epidemiologists from University College London, the World Health Organization‘s office in the Czech Republic, and the Institute of Health Information and Statistics participated in analyzing and interpreting the data. "Results from the study‘s first phase showed a rapid increase in seropositivity, demonstrating the extensive exposure of the Czech population to SARS-CoV-2 during the second wave of the pandemic: while antibodies were present in only 28% of volunteers in October and November 2020, in December 2020 and January 2021 they were present in 43%, and in February and March 2021 in 51% of volunteers. This indicates that already in March 2021, a significant segment of the Czech population was no longer immunologically naive to SARS-CoV-2 infection," commented Vojtěch Thon one of the study‘s authors from Masaryk University. "The increasing trend agrees with national data on the cumulative number of positive PCR tests and confirms the published dynamics of the epidemic. However, the measured data also indicate that the percentage of the population exposed to SARS-CoV-2 by March 2021 was significantly higher than would have been suggested by estimates based on PCR testing data alone," added Ladislav Dušek, Director of the Institute of Health Information and Statistics (UZIS). At least one-third of participants who had tested positive for antibodies did not experience any symptoms, and 28% of the seropositive individuals had never had a PCR test. These figures demonstrate the crucial role of large-scale serological studies in revealing the extent of exposure and spread of the virus in the population.

In March 2021, the Czech Republic initiated a massive vaccination campaign aimed at vaccinating the entire adult population against SARS-CoV-2 by the end of September 2021. Therefore, from March to September, all participants will have had their antibodies measured again to map the effects of the vaccination campaign on antibody development. In the third phase of testing, from October 2021 to March 2022, the persistence or decline in anti-SARS-CoV-2 IgG antibodies will be further monitored in individuals who previously contracted COVID-19 and those who have been vaccinated.

"The PROSECO study will improve epidemiological and serological characterization of the SARS-CoV-2 infection and provide valuable long-term data on the spread of SARS-CoV-2 virus and the dynamics of antibody development in a representative sample of the population," said Srdan Matič, head of the World Health Organization's Czech office, about the study. "Such data are crucial for determining the most effective vaccination strategies and for successfully managing the next phases of the COVID-19 global pandemic."

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