COVID-19 virus SARS-CoV-2

Czechoslovak Epidemiological Development

The COVID-19 epidemiology in Czechoslovakia during, and past the second wave of the epidemic between August 2, 2020 and September 12, 2021. For comparison graphs are expressed as the number of official confirmed cases per 100000 per Km2 of epidemiologically relevant population density (here, the entire surface area of Czechia and Slovakia). By November 1, 2020 only about 31 % of the Czech population (10,7 million) has reached its herd immunity against the strain of SARS-CoV-2 virus driving the first peak of the second wave. Interestingly in the Slovak population (5,5 million) only about 12% reached its immunity threshold to the same strain. Likely in combination with strict non-pharmaceutical interventions (NPIs) implemented in both nations this was exhibited as a sharp decline in the combined COVID-19 incidence. The continuation of strong interventions however was not able to prevent the second peak run up on January 10, 2021. Viral RNA genome sequencing data show that this peak was driven by a genetically different strain of the virus. By then 78% of the Czech population and 38% of Slovaks were already exposed to the pathogen and began mounting their immune response. However, it appears that much higher than 60% of SARS-CoV-2 virus population exposures are required in order to establish more durable immune protection. In Czech Republic over 124% of the population was already exposed to the COVID-19 virus (i.e. many individuals had to be exposed to number of different strains more than once) by the third, last peak of the second wave on March 7, 2021. In Slovakia it was only 56% of their population exposed on February 28, 2021. It is too early to predict whether the proximity to Czechia and both nations' population mixing would suffice to protect Slovaks in the future, however the latest Slovak run up to the third wave in September 2021 suggests that this will not be the case.

Notice that despite harsh social distancing measures deployed in both nations, the COVID-19 incidence entered into pronounced epidemiological oscillations suggesting only limited effect of non-pharmaceutical measures on COVID-19 epidemiology. Sequencing data show each oscillation peak to be associated with a different predominant viral strain.

The COVID-19 epidemiology in Czech Republic between March 22, 2020 and June 6, 2021 plotted together with its infection fatality ratio (IFR) profile. Notice none of the last two second wave peaks had appreciable impact on the resulting COVID-19 mortality.

As the nation's herd immunity was becoming established throughout the epidemic, the overall infection fatality ratio (IFR) profile was showing a continuous declining trend.

Data: WHO weekly reported SARS-CoV-2 virus positive cases.