Sydney, Mar 17 (IANS): Mortality rates between the first and second waves of Covid-19 in Europe and the United States fell further, a joint Australian-Chinese study said on Wednesday.

According to the study, lower mortality rates occurred in countries with more socialised and equitable health systems.

Researchers noted there were exceptions, including in Germany and Sweden which saw a much smaller decrease than comparable countries such as the Netherlands, which achieved nearly a 16-fold decrease in deaths, Xinhua reported.

According to the authors, the main factors contributing to the difference were that first-wave deaths disproportionately affected the elderly, and second-wave infections tended to affect younger people, as well as first wave case numbers being underestimated in Europe and the capability of health care systems to respond.

"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 2020," Max Menzies from Tsinghua University said.

Belarus was the only European nation to see an increase in mortality, as did the US states of Arkansas and Tennessee.

Meanwhile the Netherlands, Belgium, France and Denmark led Europe in reducing their reported mortality rates by more than 10-fold between the first and second waves.

The team hoped their unique methodology could be used by epidemiologists to more consistently analyse data and assess the impact of Covid-19 mortality across populations.

"We take a time series of infection rates by country, apply an algorithmic approach to chop it up into first and later waves and then do some relatively simple optimisation and calculations to determine two different mortality numbers," explained PhD student Nick James, from the University of Sydney School of Mathematics & Statistics.

The team acknowledged that their data was based on only those deaths that were reported meaning the true numbers could be different, saying there was opportunity to reapply their formula to more comprehensive data in the future.