Experts used modelling to show that infections were becoming more deadly even before the highly transmissible Alpha variant of the virus took hold.
They concluded that other factors, such as pressure on health services and the colder months, may have led to a higher number of people dying once they were infected than earlier in the year.
Writing in the journal PLOS ONE, the team, including from JP Morgan, said that “according to our models, the caseload and mortality data do not offer unequivocal evidence for higher lethality of a new variant.
“We compare these results for the UK with similar models for Germany and France, which also show increases in inferred IFR (infection fatality rate) during the same period, despite the even later arrival of new variants in those countries.
“We argue that while the new variant(s) may be one contributing cause of a large increase in IFR in the UK in autumn 2020, other factors, such as seasonality, or pressure on health services, are likely to also have contributed.”
The experts used a statistical approach known as Bayesian inference and drew on weekly data on the number of cases and the number of deaths due to Covid-19 in the UK.
They concluded that in late autumn 2020, Covid-19 did indeed become more lethal – meaning that the probability that an infected person would die from the disease increased.
It has been widely suspected this was due to the spread of the Alpha variant but the new research suggests infections were more lethal even before this point.
The team called for further studies into all the factors affecting how deadly Covid is.
Last winter, the Alpha variant was blamed for the introduction of strict measures on household mixing, including over Christmas.
The variant was first detected in September. In November, about a quarter of cases in London were the new variant, rising to around two-thirds of cases in mid-December.
According to the Office for National Statistics (ONS), there were 57,896 deaths in the UK involving Covid-19 during the first wave of the pandemic (up to August 2020).
During the second wave (September 1 to May 22, 2021), deaths were much higher at 95,967.Internet Explorer Channel Network