Epidemic potential of COVID-19 in Omsk region and assessment of the anti-epidemic measures

Aim. To study the spread of COVID-19 among the population of the Omsk region during the first 115 days of the epidemic.
Materials and Methods. We carried out a descriptive epidemiological study using the data from the Center for Hygiene and Epidemiology in the Omsk Region on the officially registered cases of COVID-19 in the Omsk Region from March 27 to July 19, 2020. The following indicators were calculated: exponential growth rate (r), basic reproduction number (R0), effective reproduction number (Rt), expected natural epidemic size and herd immunity threshold.
Results. During the indicated period, there were 5,503 cases of COVID-19 in the Omsk Region. The incidence rate was 285.60/ 0000 (95% CI 278.1 – 293.2), the case fatality rate was 1.5% for completed cases and 0.9^ for all cases. The most active spread of COVID-19 was noted in Omsk and in 5 out of 32 districts of the region (Kalachinskiy, Novovarshavskiy, Russko-Polyanskiy, Moskalenskiy, and Azov German National District). Individuals < 30 years of age were among the least involved in the epidemic process. Among the most affected groups were 55-69 years-old males and 50-64-years-old females. During the observation period, the proportion of asymptomatic forms gradually reduced along with the increase in the proportion of pneumonia cases. A manifold increase in the incidence of community-acquired pneumonia was registered in June and July 2020 compared to the average values in 2017-2019. The exponential growth rate was 6.6% per day, R0 was 1.4-1.5, Rt was 1.18, and herd immunity threshold was 28.6%. The expected size of the epidemic at sustained anti-epidemic measures was 58.0% of the population.
Conclusion. The spread of COVID-19 in the Omsk region is not sufficiently suppressed. Reduced number of asymptomatic cases and incomplete detection of COVID-19 among the patients with community-acquired pneumonia may contribute to the latent spread of the infection and complicated epidemic situation. Maintenance of the restrictive measures and acquirement of the herd immunity (over 28.6% population) may significantly reduce the spread of COVID-19 in the Omsk Region.

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