Epidemic process of COVID-19 in the Russian Federation: interim results. 2nd report

Objective. To perform an interim analysis of epidemiological parameters of COVID-19 related to contacts and secondary cases of infection in the Russian Federation. Materials and methods. We analyzed 190,856 primary COVID-19 cases and 146,996 people who had been in contact with them. We used some data of monitoring performed by the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing in January–June 2020. We characterized the foci of infection and people who had contacts with primary COVID-19 cases and secondary cases of infection. Results. Just over half (50.02%) of study participants who had contacts with COVID-19 contacted with primary patients with mild disease, whereas 45.40% of individuals contacted with patients with moderate disease and 4.58% of individuals had contacts with patients with severe disease. Patients with mild COVID-19 interacted with more people, which resulted in a greater number of secondary cases of infection. The highest proportion of both primary COVID-19 patients and people who had contact with COVID-19 was observed in the age group of 41–64 years (44.42% and 44.51%, respectively). Approximately one third of COVID-19 patients and people who had contact with COVID-19 were 18 to 40 years old (30.20% and 34.21% respectively). The proportions of children aged 0–6 years and 7–17 years among COVID-19 patients were 2.70% and 4.02%, respectively; the same proportions among those who had contact with COVID-19 cases were 1.94 and 3.13%, respectively. Household contacts were the most common ways of COVID-19 transmission in all age groups. Patients aged between 40 and 64 years played the most significant role in the transmission of this infection in different foci. Individuals from this age group comprised 42.02% of patients infected in social institutions, 43.40% of those who had household contacts, and 47.70% of those infected at work. Conclusion. Patients with mild and moderate disease aged 18 to 64 years had the highest number of contacts and, therefore, caused the highest number of secondary cases of infection. Household contacts played the most important role in COVID-19 transmission in all age groups. Among people aged 18 to 64 years, COVID-19 transmission at work was also important. In all foci of infection, the majority of patients were in the age group of 40–64 years. Our findings can be used to optimize the preventive measures for COVID-19. Key words: epidemic process, age groups, severity, contacts, COVID-19, Russia, household contacts