Intubated woman with ventilator assisted breathing due to flu or coronavirus pneumonia

(© Kiryl Lis -

CAMBRIDGE, England — Do the winter months make the coronavirus more severe for patients? A new study reveals COVID became much more lethal toward the end of the year last year.

The statistical analysis by researchers at the University of Cambridge shows that people were more likely to die if they caught COVID-19 in the closing months of 2020. The findings also suggest that multiple factors — not just the alpha variant of the virus that causes COVID — were to blame.

While the alpha variant (B.1.1.7) of the virus was more infectious than earlier widespread variants, the new analysis implies that the mortality rate increased too much for the alpha variant to be solely responsible. Furthermore, the increase in mortality started before the alpha variant had spread out.

To explore whether COVID did become more lethal in late 2020, researchers employed a statistical approach known as Bayesian inference. This enabled them to draw statistically stronger conclusions about lethality from weekly data on the number of cases and the number of deaths due to COVID in the U.K. Specifically, they used Bayesian inference to compare predictions from different mathematical simulations of COVID-19 spread and deaths, some of which incorporated increased lethality.

COVID study
Deterministic trajectories for the various model variants are shown, along with data (black). Models without change in infection fatality rate (IFR) are shown as dashed, models with change in IFR solid.
(Credit: Pietzonka et al., 2021, PLOS ONE, CC-BY 4.0)

Their findings seem to confirm that while the alpha variant was a contributing factor to increased deaths in late 2020, it wasn’t the only one. The researchers say that further study will be needed to identify those factors, but they suggested they may include increased strain on health care services and seasonality — a seasonal cycle in the severity of a virus that is commonly seen for other respiratory diseases such as flu and the common cold.

This disease’s lethality has altered over time in various places, and this information might help guide future attempts to combat it. While basic, early examinations of infection and death statistics imply that COVID-19 may have grown more fatal in the United Kingdom as recently as late 2020, more comprehensive analyses have so far remained elusive.

The findings are published in the journal PLOS One.

South West News Service writer Stephen Beech contributed to this report.

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