Experts in human ageing believe they have found a reason Covid-19 is particularly damaging and virulent among older people.

A group of tiny ribonucleic acid (RNA) molecules that should attack the virus when it tries to infect the body are diminished with age and chronic health problems, say two doctors at the Centre for Healthy Aging at Augusta University in the US.

They think this decrease helps to explain why older people and those with pre-existing medical conditions are vulnerable populations.

The Western Cape, which has had 110 (53%) of SA's 206 Covid-19 deaths, said on Tuesday that the most deaths occurred in the 51-60 age group, followed by 61-70, 41-50 and 71-80. 

Writing in the journal Aging and Disease, Sadanand Fulzele and Carlos Isales said microRNAs are on the front line when viruses invade the body.

Age and some chronic medical conditions diminish the number of microRNAs, making it easier for coronavirus to replicate.

The researchers have identified what appear to be key microRNAs involved in responding to this virus. They now want to narrow them down to the most important, and find ways to replenish them.

In 29 samples of SARS-CoV-2 - the virus which causes Covid-19 - from 17 countries on five continents, they found 873 microRNAs that target the SARS-CoV-2 genome.

They were associated with more than 72 biological processes, and many are already known to become dysregulated and/or diminish with age and medical conditions such as diabetes and cardiovascular disease.

In studies worldwide, these comorbidities have been common in people who develop serious cases of Covid-19, and in four out of five fatalities.

Isales said the 29 samples contained identical microRNAs, which indicated the virus had a uniform presence internationally and that any effective treatments or vaccines should have a broad impact.

Cocktails of microRNAs, potentially administered through the nose, might help restore sufficient levels of the key virus fighters, the researchers said.

Another question was whether younger people who developed serious Covid-19 had insufficient numbers of some of the key protective microRNAs.