Chickenpox in Poland in 2020.

Introduction: Chickenpox is an infectious disease caused by the varicella zoster virus. The characteristic feature of this virus is very high visibility of 90-95%. The most common connection is direct contact with the disease or via droplets. The United States was the first country to introduce a universal, population-based childhood varicella vaccination program in 1995. In its 25 years of implementation, this program has significantly reduced the burden of chickenpox. There was a more than 97% reduction in varicella incidence and a 90% reduction in varicella-related hospitalizations and deaths, the highest (99%) in those under the age of 20 (born after starting the vaccination programme). Chickenpox is very common in Poland. In recent years, starting from 2002, there has been an upward trend in the incidence of chickenpox, except for 2020. In 2020, a decrease in the number of cases was recorded.

Objectives: The aim of the study was to assess the epidemiological situation of chickenpox in Poland in 2020 and to compare it with the situation in previous years.

Material and methods: Evaluation of the epidemiological situation of chickenpox in Poland in 2020 was based on the results of the analysis of aggregate data published in the annual bulletins: "Infectious diseases and poisonings in Poland in 2020." and "Vaccinations in Poland in 2020". In addition, recommendations from the Protective Vaccination Program for 2020 were used.

Results: In 2020, 71,567 cases of chickenpox were registered in Poland, i.e. 39.6% less than in the previous year. The incidence of chickenpox in 2020 was 186.6 per 100,000 and was lower than in 2019. The lowest incidence was recorded in the Świętokrzyskie Voivodship - 118.5/100,000, while the highest in the Kujawsko-Pomorskie Voivodeship - 263.5/100,000. Most cases concerned children aged 0-4 years (36,661). The incidence of chickenpox in men was higher than in women, and in rural areas higher than in urban dwellers. Hospitalization due to chickenpox in 2020 covered 1,368 people, which accounted for 0.51% of the total number of registered cases.

Conclusions: In 2020, there was a decrease in the number of cases of chickenpox compared to the previous year. The lower incidence may have been the result of reduced transmission of the varicella virus due to changes in the health behavior of the population during the COVID-19 pandemic (isolation measures and the introduction of a lock down throughout Poland limiting the activity of the population).