The study, published in The Lancet Infectious Diseases, looked at data from last fall in the U.K., shortly after the variant was first detected. It soon spread rapidly, eventually becoming the dominant strain circulating in the country.
The new findings add to scientists' ever-evolving understanding of the U.K. variant, known as B.1.1.7, at a crucial time in the pandemic, as it and other variants are circulating widely in other countries.
Researchers looked at Covid-19 patients who were admitted to University College London Hospital and North Middlesex University Hospital from Nov. 9 to Dec. 20. The scientists sequenced virus samples from 341 patients, finding that 58 percent were positive for the U.K. variant and that 42 percent had been infected with a different strain.
The researchers then compared the severity of symptoms between the two groups and found that patients infected with the B.1.1.7 variant were not at increased risk of becoming severely ill or dying. The study zeroed in on a time when the U.K. variant was just gaining a foothold in London — and as the U.K.'s vaccination program was getting underway.
The study found that samples from patients with the B.1.1.7 variant had greater quantities of virus, or higher "viral loads," but it is not yet clear why.
"One idea for why this variant is more transmissible could be that patients are making more virus," Frampton said.
He said that while the researchers did not find an association between the U.K. variant and the severity of illness, patients hospitalized with the B.1.1.7 variant at the time were more likely to be under age 60 and from ethnic minority backgrounds.
Patients with B.1.1.7 were also more likely to be given oxygen. Frampton said that was not necessarily an indication of more severe disease and that more research is needed.
A paper published last month in the journal Nature found that the B.1.1.7 variant may be associated with a 61 percent higher risk of death than pre-existing variants. Earlier in March, research published in The BMJ found that people over age 30 had a 64 percent higher risk of death from the U.K. variant than from earlier strains. In that study, however, the scientists said the "absolute risk of death in this largely unvaccinated population remains low."
Dr. Eric Topol, director of the Scripps Research Translational Institute in California, who was not involved with the new study, said the conflicting results show how much there is still to learn about the B.1.1.7 variant.
"The new findings don't nullify the other papers — they just make you think," he said. "Maybe the truth is somewhere in the middle. This study says there's no higher death rate, but they did find more need for oxygen, so there's something going on there with respect to this variant."
Although there have been some indications that the B.1.1.7 variant is affecting young people more than previous strains, there is not enough data to know for sure, Topol said. And it can be difficult to separate out other factors that may account for the trend.
"That's one of the tricky things about this variant epidemiology," he said. "There are a lot of moving parts — age, resources, co-existing conditions — and you can't always adjust for all of that stuff."
A variant that is more contagious is likely to mean there will be more cases among children and young people, who previously were not thought to be most vulnerable to Covid-19.
"It doesn't mean the virus is preferentially finding them. It just means we would expect to see more in younger people because, across the board, it causes higher viral loads and more spread," Topol said.
Another area that will require more research is the effect of the U.K. variant on immunity. A separate study published Monday in The Lancet Public Health examined self-reported data from nearly 37,000 people in the U.K. and found that reinfection rates were low. The findings were based on app-submitted surveillance data over 13 weeks from September to December, when the number of cases of the U.K. variant exploded in London and southeastern England.
The researchers found that only 249 out of 36,509 people of those who reported positive tests before Oct. 1, or 0.7 percent, tested positive again more than 90 days later. In other words, people who had been infected with a pre-existing variant were not at higher risk of being reinfected with the B.1.1.7 variant.
"This suggests that B.1.1.7 does not evade immunity that people develop from infection from prior strains of the disease," said a lead author of the paper, Mark Graham, a research fellow at King's College London.
Graham and his colleagues are monitoring for reinfections, particularly as bigger slices of the population in the U.K. and elsewhere become fully vaccinated. Studies have shown that the vaccines currently available offer strong protection against the U.K. variant, and Graham said long-term studies of immunity will offer more clarity about not only the B.1.1.7 strain but also other potentially worrisome variants that could arise.
"Vaccine rollout is going remarkably well in the U.K., and it's making a huge difference, but the one unknown factor that could derail this progress is new variants," he said. "Understanding how that could affect us will be hugely important."
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