Comparable seasonal pattern for COVID-19 and flu-like illnesses

Area of Science:

• Epidemiology
• Infectious Disease Dynamics
• Public Health

Background:

• Early in the COVID-19 pandemic, its seasonality was hypothesized to resemble that of Influenza-Like Illnesses (ILI).
• This study investigated the COVID-19 seasonality hypothesis one year into the pandemic.

Purpose of the Study:

• To test the hypothesis that COVID-19 exhibits multi-wave seasonality, similar to ILI.
• To compare the temporal patterns of COVID-19 incidence with historical ILI data.

Main Methods:

• Calculated average annual ILI time-series (2016-2019) and compared with COVID-19 time-series (2020-2021) in the Netherlands.
• Utilized a standardized logarithmic infection scale for plotting time-series.
• Employed correlation coefficients and univariate regression analysis to assess the association between COVID-19 and ILI time-series.

Main Results:

• A strong and highly significant correlation was found between COVID-19 and ILI time-series.
• COVID-19 peaks consistently occurred during the flu season, with lows in the opposing period.
• The COVID-19 pandemic displayed multi-wave characteristics: a short first wave at the flu season's end and a longer, more intense second wave during the subsequent flu season.

Conclusions:

• COVID-19 incidence patterns are highly similar to ILI patterns in temperate climates like the Netherlands.
• The COVID-19 pandemic's wave characteristics align with those of previous respiratory pandemics.
• Environmental factors such as solar radiation, temperature, and humidity likely drive COVID-19 seasonality, similar to ILI.