Now a team in Poland claim that, after age, weight and gender, a specific gene is the most crucial factor for determining severe Covid risk.
The gene is present in around 14 per cent of Polish people, up to nine per cent of Europeans and 27 per cent of Indians, they say.
Experts said the research could be used to detect patients who are in more urgent need of care, should they end up in hospital.
It could also encourage those carrying the gene to get a vaccine, as only half of Poles are double-jabbed.
Health Minister Adam Niedzielski said: “After more than a year and a half of work it was possible to identify a gene responsible for a predisposition to becoming seriously ill (with coronavirus).
“This means that in the future we will be able to… identify people with a predisposition to suffer seriously from Covid.”
Professor Marcin Moniuszko, of the Medical University of Bialystok, led the research, which has not been published but was presented at a press conference.
Researchers looked at around 1,500 Covid patients, the university said.
The study showed that our genetic profile is “even more important” than existing underlying illness, a press release claimed.
It said having one of the genes meant that someone would be “more than twice as likely to be infected or even to die from Covid-19”.
The group said it would a “relatively simple genetic test” could be used to identify people with the risky gene.
Prof Moniuszko said: “Such a test may help to better identify people who, if infected, may be at risk of a rapid course of the disease before infection occurs.
“Then, such people could receive special care, increased protection both preventive (additional doses of protective vaccinations) and medical (new treatments).”
Other studies have uncovered genetic variations that make a person more vulnerable to the virus.
In November, British scientists said they had identified a version of a gene that may be associated with double the risk of lung failure during Covid.
Oxford University pin-pointed a chunk of DNA that blocks lung cells from fighting off the virus.
The gene, called LZTFL1, doubles the risk of Covid death.
More than one in six Brits and Europeans could have this gene, the study found.
But people from South Asian heritage face an even greater threat.
A massive 61.2 per cent of people from the region are thought to have it.
Scientists say it could explain why South Asian people in the UK have been so hard hit by the coronavirus.
However, they stressed the gene was not the sole reason.
There are several other important factors among these communities that are thought to contribute to the higher mortality rates.
Some two per cent of people with Afro-Caribbean ancestry carried the higher risk genotype.
This further shows the genetic link could not wholly explain the higher death rates reported for black and minority ethnic communities in the UK.