COVID-19 seasonality in temperate countries

Abstract

Introduction While the beneficial effect of vaccination, restrictive measures, and social distancing in reducing mortality due to SARS-CoV-2 is intuitive and taken for granted, seasonality (predictable fluctuation or pattern that recurs or repeats over a one-year period) is still poorly understood and insufficiently taken into consideration. We aimed to examine SARS-CoV-2 seasonality in countries with temperate climate. Methods We identified countries with temperate climate and extracted average country temperature data from the National Center for Environmental information and from the Climate Change Knowledge Portal. We obtained mortality and vaccination rates from an open access database. We used the stringency index derived from the Oxford COVID-19 Government Response Tracker to quantify restriction policies. We used Spearman's and rank-correlation non-parametric test coefficients to investigate the association between COVID-19 mortality and temperature values. We employed multivariate regression models to analyze how containment measures, vaccinations, and monthly temperatures affected COVID-19 mortality rates. Results The time series for daily deaths per million inhabitants and average monthly temperatures of European countries with a temperate climate had a negative correlation (p < 0.0001 for all countries, 0.40 < R < 0.86). When running multivariate regression models with country fixed effects, we noted that mortality rates were significantly lower when temperature were higher. Interestingly, when adding an interaction term between monthly temperatures and vaccination rates, we found that as monthly temperatures dropped, the effect of the vaccination campaign on mortality was larger than at higher temperatures. Discussion Deaths attributed to SARS-CoV-2 decreased during the summer period in temperate countries. We found that the effect of vaccination rates on mortality was stronger when temperatures were lower. Stakeholders should consider seasonality in managing SARS-CoV-2 and future pandemics to minimize mortality, limit the pressure on hospitals and intensive care units while maintaining economic and social activities.

Impacts of exposure to air pollution, radon and climate drivers on the COVID-19 pandemic in Bucharest, Romania: A time series study

“…Like for other temperate countries, in Romania and its capital Bucharest, there is a linkage between climate variables seasonality and direct impacts on COVID-19 viral infection seasonality. This result was demonstrated also by other studies ( D'Amico et al, 2022 ; Zoran et al, 2022 ).…”

“…Also this study found significant anticorrelations between daily average Planetary Boundary Layer heights over Bucharest city and daily new COVID-19 confirmed cases and mortality as follows: rDNC = −0.53, p < 0.01 and respectively rDND = −0.57, p < 0.01. High levels of daily PBL of (1607.19 ± 526.06) m registered during the first COVID-19 wave in Romania may explain the low severity of the first COVID-19 wave in Bucharest city in comparison with the rest of some European metropolitan cities ( D'Amico et al, 2022 ; Zoran et al, 2020a ; Zoran et al, 2020b ; Zoran et al, 2021 ). An opposite situation was recorded during the second, and the fourth COVID-19 waves when the daily average PBL heights recorded abnormally low values per each wave and season, being respectively of (538.74 ± 293.26) m, and (920.23 ± 603.25) m, that can explain high rates of infectivity and deaths in Bucharest city.…”

“…Among COVID-19 pandemic multi-risk factors, outdoor and indoor environmental exposures are interlinked with social, demographic, and evolutionary ( Destoumieux-Garzon et al, 2022 ). Clinical and host-specific genetic factors may be related to environmental seasonality risk factors for SARS-CoV-2 infection and outcomes ( D'Amico et al, 2022 ; Casado-Aranda et al, 2021 ; Iqbal et al, 2021 ; Nishiura et al, 2020 ; Luo et al, 2020 ; Walls et al, 2020 ; Cao et al, 2020 ). Outdoor environmental factors (climate and air quality) are mainly responsible for the dispersal, diffusion, and infectivity rate of the SARS-CoV-2 pathogens and their new variants virions ( Yuan et al, 2021 ; Hassanzadeh et al, 2020 ; Islam et al, 2021 ; Huang et al, 2020 ; Amin et al, 2020 ).…”

Impact of implementation timing on the effectiveness of stay-at-home requirement under the COVID-19 pandemic: Lessons from the Italian Case

“…Lastly, seasonality played a role in the trajectory of the pandemic during the first wave of COVID-19 in Italy [ 67 , 68 ]. Italy presents differences in terms of temperature and humidity throughout the peninsula, but since the entire country is within the Northern Tropic and more precisely the Mediterranean area, we omitted the seasonal component at a regional level in line with other studies [36] .…”

Questioning the seasonality of SARS-COV-2: a Fourier spectral analysis

“…Along this line of research, remarkable are the studies of D’Amico et al who used a multivariate regression to assess the influence of temperatures and vaccinations on mortality rates in temperate climate countries. They found a negative correlation with temperatures and discovered that the vaccination’s effect grew larger as the temperature decreased 4. Similarly, Ma et al studied the problem in the USA using a generalised additive mixed model.…”