Dozens of Britons have had four bouts of Covid-19 and thousands more have been infected three times, officials say.
But while many people have been reinfected multiple times, others appear to have avoided contracting the coronavirus despite coming into close contact with cases — a disparity that scientists have struggled to explain. Here are some of the more plausible theories.
An international consortium of researchers has launched a study to examine whether a small proportion of people could be genetically resistant to Covid-19. The identification of such protective genes could lead to the development of new treatments for the coronavirus.
The scientists appealed worldwide last October to find apparently Covid-resistant people to take part in the study, with the aim of recruiting at least 1,000 in total. “Of particular interest are people who have shared a home and bed with an infected partner – couples known as discordant couples,” the scientific journal reported nature.
The team from ten research centers worldwide had already recruited around 500 potential candidates. And within two weeks of their hunt beginning, another 600 people had reportedly signed up to sign up.
“I didn’t think for a second that people who were exposed and didn’t appear to be infected would come to us,” said study co-author Jean-Laurent Casanova of Rockefeller University in New York.
The potential resistance the study participants may have “is known to exist for other diseases, including HIV, malaria and norovirus.” The guardreported science correspondent Linda Geddes.
“In these cases, a genetic defect means that some people lack a receptor that is used by the pathogen to enter cells so they cannot be infected,” Geddes explained.
Director of Studies András Spaan, Professor at from Rockefeller University in New York that “it could well be that some individuals have such a defect in a receptor used by Sars-CoV-2,” the virus that causes Covid-19.
However, Spaan “thinks it is unlikely that the majority of those who have avoided Covid are genetically resistant, even if they have partial immune protection,” Geddes said.
A study led by a team of Imperial College London found that people who have fought colds may have a lower risk of contracting Covid-19.
“We found that large amounts of pre-existing T cells, produced by the body when infected with other human coronaviruses such as the common cold, can protect against Covid-19 infection,” said study co-author Rhia Kundu from Imperial’s National Heart and Lung Institute.
Researchers tested blood in September 2020 – before Covid vaccines were rolled out – from 52 people living with others who had just tested positive for the coronavirus. A total of 26 contracted Covid during the 28-day study period.
To find out why the other half of the group escaped infection, the researchers looked at the role played by T cells, which are “a crucial part of the body’s immune system,” he said BBC.
Some of these T cells “kill any cells infected with a particular threat,” such as a cold virus, the broadcaster explained. And after a cold infection, some “remain in the body as a memory bank, ready to defend against future onslaughts of the virus.”
According to a study published in nature In January, the 26 test subjects who had not contracted Covid had “significantly higher levels” of pre-existing T cells induced by previous cold coronavirus infections and also proteins from the Sars-CoV-2 virus recognize crosswise.
However, study co-author Kundu stressed that “no one should rely on this alone,” adding, “The best way to protect against Covid-19 is to get a full vaccination, including the booster dose.”
The team and other scientists also pointed out that not all colds are coronaviruses. dr Simon Clarke, from the University of Reading, who was not involved in the study, said: “It could be a serious mistake to think that anyone who has recently had a cold is protected from Covid-19 as coronavirus only accounts for 10% -15% of colds.”
blood group connection
Some research suggests that people with blood types A and AB are more susceptible to contracting Covid, while those with blood type O are less likely to test positive for the virus.
Two studies published in the blood advances Journal in October 2020 showed a possible link between blood type and susceptibility to Covid. The first, by Danish researcherscompared health registry data from more than 473,000 people tested for Covid-19 to data from a control group of more than 2.2 million untested people.
“Among the Covid-19 positives, they found fewer people with blood type O and more people with blood types A, B and AB,” she reported science daily.
the second study examined data from 95 critically ill Covid patients hospitalized in Vancouver, Canada. It has been found that patients with blood types A and AB are more likely to require mechanical ventilation and dialysis for kidney failure.
Despite these results, however, many scientists are not convinced of the alleged blood group connection. A review of nearly 108,000 Covid patients in the US published in a paper in the Journal of the American Medical Association found no such link in April 2021 and said more research was needed.
A less scientific possible explanation for why some people appeared to have avoided Covid is that they were actually infected but were showing no symptoms.
Accordingly ReutersGovernment estimates for the proportion of asymptomatic omicron infections in the UK have ranged from 25% to 54%.
And while many people continue to routinely test for Covid, a recent study by Imperial College London found that lateral flow testing may miss a “significant” number of infections.
An analysis by a team from the university found that the Innova-branded tests missed between 20% and 81% of positive cases.
Concerns have also been raised that many people performing such tests make mistakes – e.g. E.g. eating or drinking within half an hour or forgetting to blow your nose beforehand – which can lead to incorrect results.
As one Twitter user asked, “Are others wondering if they’re really testing negative or just not shoving this thing up their noses far enough?”
https://www.theweek.co.uk/news/science-health/956261/how-have-some-people-avoided-covid How did some people avoid contracting Covid-19?