New Statistical Analysis Shows COVID-19 Became Much More Lethal in Late 2020

A new statistical analysis supports the belief that COVID-19 became more deadly in the UK by the end of 2020, while also suggesting that multiple factors – not just the alpha variant of the virus causing COVID-19 – were to blame. Patrick Pietzonka of the University of Cambridge, UK, and colleagues present these findings November 24, 2021 in the open-access journal PLOS ONE.

Studying how the lethality of COVID-19 has changed over time in different regions could aid ongoing efforts to tackle this disease. While simple, preliminary reviews of infection and mortality data suggest that COVID-19 may have become more deadly in the UK by the end of 2020, more rigorous analyzes have been lacking.

Deterministic trajectories for the different model variants are shown, along with data (black). Models with no change in infection mortality rate (IFR) are shown as dashes, models with change in IFR solid. Credit: Pietzonka et al., 2021, PLOS ONE, CC-BY 4.0

To investigate whether COVID-19 did indeed become more deadly in late 2020, Pietzonka and colleagues used a statistical approach known as Bayesian inference. This enabled them to draw statistically stronger conclusions on lethality from weekly data on the number of cases and deaths from COVID-19 in the UK. More specifically, they used Bayesian inferences to compare predictions from different mathematical simulations of the spread of COVID-19 and deaths, some of which involved increased lethality.

This analysis suggests that COVID-19 did indeed become more deadly in the UK in late autumn 2020, meaning that the chances of an infected person dying from the disease increased.

According to previous speculations, this increase in lethality was caused by the alpha variant (B.1.1.7) of the SARS-CoV-2 virus, which was more contagious than previously widespread variants in the UK. However, the new analysis suggests that lethality increased at a greater rate than the alpha variant would have explained, and that the increase in lethality started before the alpha variant became widespread.

These findings suggest that while the alpha variant contributed to increased lethality in late 2020, other factors were also involved. Further research will be needed to identify those factors, but the authors suggest they may include increased health care pressures and seasonality — a seasonal cycle in the severity of a virus commonly seen for other respiratory illnesses such as the common cold and flu.

Reference: “Bayesian inference across multiple models suggests sharp increase in UK COVID-19 lethality by late 2020” Nov 24, 2021, PLOS ONE.
DOI: 10.1371/journal.pone.0258968