Background During the first wave of COVID-19 it was hypothesized that COVID-19 is subject to multi-wave seasonality, similar to Influenza-Like Illnesses since time immemorial. One year into the pandemic, we aimed to test the seasonality hypothesis for COVID-19. Methods We calculated the average annual time-series for Influenza-Like Illnesses based on incidence data from 2016 till 2019 in the Netherlands, and compared these with two COVID-19 time-series during 2020/2021 for the Netherlands. We plotted the time-series on a standardized logarithmic infection scale. Finally, we calculated correlation coefficients and used univariate regression analysis to estimate the strength of the association between the time-series of COVID-19 and Influenza-Like Illnesses. Results The time-series for COVID-19 and Influenza-Like Illnesses were strongly and highly significantly correlated. The COVID-19 peaks were all during flu season, and lows were all in the opposing period. Finally, COVID-19 meets the multi-wave characteristics of earlier flu-like pandemics, namely a short first wave at the tail-end of a flu season, and a longer and more intense second wave during the subsequent flu season. Conclusions We conclude that seasonal patterns of COVID-19 incidence and Influenza-Like Illnesses incidence are highly similar, in a country in the temperate climate zone, such as the Netherlands. Further, the COVID-19 pandemic satisfies the criteria of earlier respiratory pandemics, namely a first wave that is short-lived at the tail-end of flu season, and a second wave that is longer and more severe. This seems to imply that the same factors that are driving the seasonality of Influenza-Like Illnesses are causing COVID-19 seasonality as well, such as solar radiation (UV), temperature, relative humidity, and subsequently seasonal allergens and allergies. Highlights • Time-series of COVID-19 and Influenza-Like illnesses have highly similar seasonal patterns in the Netherlands. • COVID-19 satisfies the seasonal criteria of earlier flu-like pandemics. • The implication is that the seasonal factors driving flu season, are also responsible for COVID-19 seasonality. • Determined seasonality by applying comparative time-series analysis and a standardized logarithmic infection scale.
【저자키워드】 seasonality, respiratory viruses, COVID-19 incidence, influenza-like illnesses, 【초록키워드】 COVID-19, pandemic, COVID-19 pandemic, Infection, Characteristics, Pandemics, second wave, temperature, incidence, flu, First wave, association, Hypothesis, Analysis, Netherlands, criteria, allergen, regression analysis, Radiation, Factor, subject, average, allergies, zone, correlation coefficient, driving, country, Result, responsible, significantly, subsequent, calculated, correlated, illness, meet, short-lived, 【제목키워드】 COVID-19, illness,