Pandemic's second wave less deadly than first in U.S., Europe, study finds

March 16 (UPI) -- The second wave of the COVID-19 pandemic in the United States and Europe was not as deadly as the first, according to an analysis published Tuesday by the journal Chaos.

Deaths attributed to the virus declined roughly 10-fold in Europe and about four-fold in the United States from the first wave of infections to the second, the data showed.

The first wave is generally considered the start of the pandemic in March and April 2020, while the second began in most parts of the United States and Europe in the fall.

"Our work shows sharp drops in mortality with respect to reported cases and deaths," study co-author Max Menzies said in a statement.

However, "the problem will always be, what is the true number of cases in the early first wave? We may never know, but we imagine future research and analysis will try to determine it," said Menzies, a post-doctoral fellow in mathematics at Tsinghua University in Beijing, China.

The decline in deaths from COVID-19 is likely due to improvements in patient treatment, including the use of steroids in hospitalized patients, as well as potential undercounting of cases and deaths in many parts of the world, according to Menzies and his colleagues.

For their analysis, the researchers used applied mathematics, including time series analysis, to study the progression of COVID-19 cases to deaths during the pandemic's different waves on a country-by-country basis.

Time series analysis is a statistical approach to spot trends by taking data on one or more variables -- in this case, cases and deaths -- at equally spaced points of time, the researchers said.

"We take a time series, [and] apply an algorithmic approach to chop it up into first and later waves," co-author Nick James, a graduate student at the University of Sydney, said in a statement.

Through much of the United States and Europe, deaths from COVID-19 declined significantly from the first to the second wave, particularly in wealthier regions.

For example, between the two waves, virus death rates declined 16-fold in the Netherlands and about 14-fold in France and Denmark. They also dropped about 10-fold in Ireland, Spain and Britain.

However, they actually increased slightly in Belarus and Malta and stayed flat in places such as Albania, Bulgaria and Serbia.

In the United States, between the first and second waves, death rates dropped nine-fold in Vermont, eight-fold in New Jersey and seven-fold in New York. The latter two states were hit particularly hard during the first wave of the pandemic.

However, deaths increased slightly in Arkansas and Tennessee and remained stable in Alabama, Arizona, California, Georgia, Mississippi, Nebraska, Nevada, North Dakota and Texas.

"We think answering these questions is important, and to answer this for all of Europe, not just the wealthier Western countries," said Menzies, from Tsinghua University.

"In Belarus, for example, the mortality rate actually increased during its second wave, while Ukraine and Moldova were still in their first wave as of the end of November," he said.