LONDON — A new and potentially more contagious variant of the coronavirus has begun to outpace other versions of the virus in Britain, putting pressure on the government to shorten people’s wait for second doses of vaccines and illustrating the risks of a faltering global immunization drive.
The new variant, which has become dominant in India since first being detected there in December, may be responsible in part for a grievous wave of infections across Southeast Asia, including Nepal, where people have been dying in hospital corridors and courtyards. But efforts to understand the variant picked up once it began spreading in Britain, one of at least 49 countries where it is present. Scientists there are sequencing half of all coronavirus cases amid a push to complete the reopening of its economy.
The preliminary results out of Britain, drawn from only a few thousand cases of the variant, contained both good and bad news, scientists said.
The variant, known by evolutionary biologists as B.1.617.2, is “highly likely” to be more transmissible than the variant behind Britain’s devastating wintertime surge, government scientists have said. That earlier variant, known as B.1.1.7, was itself considerably more contagious than the one that first emerged last year in Wuhan, China.
A Public Health England report published this weekend provided signs that government scientists said were consistent with a more transmissible virus: The variant first seen in India was roughly 50 percent more likely than B.1.1.7 to be transmitted to the close contacts of an infected person. Government scientists said last week that it could be anywhere from a few percentage points to 50 percent more contagious than B.1.1.7.
Helpfully for Britain and other wealthy nations, the latest worrisome variant has emerged at a less dire moment of the pandemic. More than four out of every five people in England above the age of 65 — among the groups most vulnerable to the virus — have been given both doses of a coronavirus vaccine, driving down hospitalizations and deaths.
And a new study by Public Health England offered reassuring signs that fully vaccinated people were about as well protected from the variant first detected in India as they were from other forms of the coronavirus.
The Pfizer-BioNTech vaccine offered 88 percent protection against the variant first sampled in India, only a slight drop from the 93 percent protection given against the variant from Britain, Public Health England said. The AstraZeneca-Oxford vaccine was 60 percent effective against the variant from India, compared to 66 percent effective against the one first seen in Britain.
Because Britons started receiving AstraZeneca’s vaccine later than Pfizer’s, they have been followed for a shorter period, meaning that the effectiveness figures for that vaccine may underestimate the true numbers, scientists said. Other studies in England have shown little to no difference between the effectiveness of the Pfizer and AstraZeneca vaccines.
For now, a rise in cases of the variant from India has not caused an overall surge in the virus in Britain. And not all scientists are convinced that the variant is as contagious as feared. The true test will be whether it surges in other countries, especially those — unlike Britain — that are grappling with high case counts of other variants, Andrew Rambaut, a professor of molecular evolution at the University of Edinburgh in Scotland, wrote on Twitter.
In Britain, part of its rapid growth may have to do with the particular places it was first introduced. Bolton, in northwest England, where the new variant is most advanced, is a highly deprived area with tightly packed housing that could be hastening its spread, scientists said.
“We do not know if the increase in transmissibility is the result of specific mixing patterns, or super-spreading events,” a group of researchers led by Robert Challen of the University of Exeter reported on May 11, in a study that was among those presented to an influential government advisory group.
That government advisory body said several days later that it had “high confidence” that the variant first seen in India was indeed more contagious, warning that a “substantial resurgence of hospitalizations” was possible. It said that the variant was gaining a foothold in diverse parts of Britain where “contact patterns or behaviors” alone could not explain its spread.
It is not clear if the variant from India is any deadlier than B.1.1.7.
With cases of B.1.1.7 falling, the variant first seen in India now accounts for roughly half of the sequenced coronavirus cases being monitored by Public Health England. The agency’s scientists have said it was likely to replace B.1.1.7 as England’s dominant virus within a month, a startling turnabout so soon after B.1.1.7 swept much of the world.
“For countries that are starting to struggle with B.1.1.7, they now know they have an even faster one close by,” said Devi Sridhar, a professor of global public health at the University of Edinburgh in Scotland.
In the United States, which has detected more than 800 cases of the variant from India, a glut of vaccines has given health officials a ready supply of tools for fighting the fast-evolving virus.
But even other wealthy nations, like Britain, are in more difficult positions. To stretch its supply of vaccines, the country extended the gap between the first and second doses of AstraZeneca, Pfizer and Moderna vaccines to up to 12 weeks, longer than the periods studied in clinical trials.
Health officials argued that giving more people the partial protection of a single dose would help the country escape a deadly surge of cases. And the AstraZeneca vaccine appeared to be more potent when its two doses were given at a longer interval.
The gambit appeared to work: Public Health England estimated last week that the immunization campaign had forestalled more than 10,000 deaths and 35,000 hospitalizations in older people.
And yet the latest studies about the variant from India have suggested that those gains came at a price. While fully vaccinated people are amply protected against the new variant, people with only a single dose remain vulnerable, Public Health England said.
A first dose of either the Pfizer or AstraZeneca vaccines provided only about 34 percent protection against the variant first seen in India, a relatively steep drop from the roughly 51 percent protection a single dose of either of those vaccines offer against the earlier variant from Britain.
(There was considerable statistical uncertainty about the 34 percent effectiveness figure, and some scientists offered reasons that it may end up being higher.)
Many Britons are only partially vaccinated. Of the 38 million people given a first vaccine dose in Britain, more than 15 million were still waiting for their second doses, including many in their 40s, 50s and early 60s.
“It may come back to bite us,” Simon Clarke, an associate professor in cellular microbiology at the University of Reading, said of Britain’s delayed dosing strategy. “There’s clear evidence now that one dose isn’t as good as two doses, at least with the Indian variant, and I suspect with others as well.”
In response, the government has sought to tighten the space between two doses for some people, and — belatedly, in the view of many scientists — begun experimenting with ways to encourage sick people to isolate.
Some scientists have urged the government to go further by dramatically closing the gap between doses of the Pfizer or Moderna vaccine, for instance, and rerouting those shots to cities hardest hit by the variant from India. Because the AstraZeneca vaccine appears most protective with a 12-week dosing interval, those scientists said, using it meant leaving people only partially vaccinated for a period of time.
At the very least, Professor Sridhar said, people needed to be reminded to remain cautious until they were fully vaccinated.
Prime Minister Boris Johnson’s plan to scrap almost all remaining lockdown restrictions on June 21 rests in large part, scientists said, on how many second doses Britain can administer in the coming weeks.
For many poorer nations, starved for vaccines, there is little choice but to leave long delays between first and second doses. Some of them are uncertain about when shipments of second doses will arrive. Large portions of those countries remain entirely unprotected.
If the variant from India spreads as quickly in other countries as it has in Britain, the burden on unvaccinated nations may grow.
“It’s a warning,” Professor Sridhar said. “What we’re seeing in India is being repeated in Nepal, it’s being repeated in other countries. You need to get ahead of it.”