New research from England’s public health service has confirmed a suspicion spawned by bursting hospital wards across the United States: The delta variant of the coronavirus not only spreads 50% more readily than the Alpha variant it rapidly overtook, it’s also making unvaccinated people sicker.
Through most of April and May, unvaccinated Britons who were infected by the delta variant were more than twice as likely to be admitted to hospitals than were their unvaccinated peers who were infected with the Alpha strain, which was first identified in the United Kingdom.
In addition, unvaccinated people infected with delta were more likely than those infected with Alpha to seek care in a hospital’s emergency department, the new study found.
The report, published late Friday in the journal Lancet Infectious Diseases, is considered the largest and most detailed accounting to date of the delta variant’s impact on the pandemic. It is based on the health records of 43,338 Britons who tested positive for coronavirus infections between March 29 and May 23 of this year and whose samples were genetically sequenced.
The findings not only confirm that surges involving the delta variant will drive more people into hospitals and strain medical resources: By implication, they suggest that when the variant attacks a population with large numbers of unvaccinated people, its victims become more acutely ill.
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Its results may help explain why the United States is now admitting an average of 12,285 patients to hospitals each day — a rate that has climbed steadily since late July.
The delta variant was first detected here in mid-May and now accounts for 99% of all U.S. infections. Communities with low vaccination rates have seen their hospitals and emergency departments overwhelmed with COVID-19 patients.
“We knew we are seeing more patients, and we suspected that delta is sending more people to hospitals,” said Ali H. Mokdad, a population health specialist at the University of Washington’s Institute for Health Metrics and Evaluation. “What’s surprising is the extent of it — how big the difference is.”
Hospitalization practices for COVID-19 are bound to differ from place to place, and some people will seek out hospital care more readily than others. The new study controls for this by accounting for age, gender and the economic and social circumstances that influence a person’s likelihood of seeking hospital care and getting it.
In the study’s roughly two-month span, genetic surveillance showed that the then-dominant Alpha variant was quickly being muscled aside by the newer genetic strain first detected in India. Between March and late May, delta went from virtually undetectable to accounting for half of all genetically sequenced infections in England.
Among vaccinated people, an infection with the delta variant was no more likely to lead to hospital admission than a so-called breakthrough infection involving the Alpha variant.
While that finding is reassuring — and in line with evidence that vaccines protect well against severe illness and hospitalization — it is of limited value to U.S. public health planners. The number of breakthrough infections seen at that early point in Britain’s vaccination campaign was too small to generate confident conclusions. And the United Kingdom has relied heavily on a vaccine developed by Oxford and AstraZeneca, which is not used in the United States.
The results echo early research conducted in Scotland that suggested in June that infection with the delta variant doubled the risk of hospitalization compared with the Alpha variant.
But even as hospital wards here have filled with unvaccinated Americans, experts at the U.S. Centers for Disease Control and Prevention have been wary of saying the delta variant itself is more dangerous.
The increase in hospitalizations could be the natural consequence of the variant’s greater penchant for spreading, CDC experts have said: As more people get infected, the number of people who need hospitalization will rise accordingly.
Dr. Eric Topol, director of the Scripps Research Translational Institute in La Jolla, said the rigorous accounting of England’s experience as the delta variant moved in offers stronger evidence that the strain isn’t simply infecting more people more quickly.
“Everything is coming together to suggest that it’s not just the spread” that has packed hospital wards, he said.
A welter of new studies has shown that infection with delta causes a steep rise in the amount of virus in a person’s nose and upper airways. That makes it easier for the virus to spread to others, and it infects them with a higher dose of virus.
In unvaccinated people, the massive viral invasion can overwhelm the immune system’s ability to respond quickly enough. Within a couple of weeks of infection, more people find themselves sick enough to go to a hospital.
“We don’t know the mechanism” for this increased level of illness, Topol said. “But it’s becoming increasingly clear there’s something about delta.”
“This is an important report,” he added.