New York, Nov 29 (IANS): In the pandemic's early phases, most deaths were among older adults, but in 2021, deaths in younger persons increased while deaths in older persons decreased, a new study has found.

The increase in "years of life lost" was due to a shift toward younger people dying of Covid-19 during the first two years of the pandemic, according to the study by two investigators from Brigham and Women's Hospital in the US.

Earlier in the pandemic, age and pre-existing conditions played a major role in developing public health advice.

But by early 2021, the Covid-19 landscape had shifted completely and vaccines became available, treatments advanced and people's behaviours changed.

While 2020 Covid death rates were high among older adults, those older adults exhibited a relatively higher vaccination rate and adhered more strictly to nonpharmaceutical interventions throughout 2021.

Such systemic and behavioural changes in response to Covid-19 impacted mortality rates and determined what ages, in what years, were higher risk.

"There were a lot of changes between the first and second years of the Covid-19 pandemic," said corresponding author Mark Czeisler in the study published in Annals of Internal Medicine.

Between March 2020 and October 2021, COVID-19 maintained a spot as one of the top-five causes of death for US adults.

Its specific rank within that top-five, however, changed based on age, demonstrating a greater proportion of young people prematurely dying from COVID-19 in 2021.

Researchers quantified this downward age-shift in COVID-19 deaths, using 'Years of Life Lost' (YLL) rather than mortality.

Using these resources, the team calculated per cent of Covid-19 deaths and YLL per death.

Despite 20.8-per cent fewer Covid deaths in 2021 versus 2020, YLL increased 7.4-per cent.

"A shift in Covid-19 mortality to relatively younger people in the second pandemic year contributed to markedly increased premature mortality from this increasingly preventable death," said Czeisler.

"Understanding the factors that contribute to this age shift is critical as we continue developing our knowledge of the COVID-19 pandemic," the researchers noted.