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Some Vaccinated People Are Dying of Covid-19. Here's Why Scientists Aren't Surprised.

The Wall Street Journal. logo The Wall Street Journal. 7/2/2021 Jason Douglas, Stephen Fidler
© Yui Mok/pa/Zuma Press

LONDON—As the Delta variant of the coronavirus surges through the U.K., almost half of the country’s recent Covid-19 deaths are of people who have been vaccinated. But doctors and scientists aren’t sounding the alarm about the apparently high proportion of deaths among the vaccinated population.

On the contrary, they say the figures so far offer reassurance that vaccines offer substantial protection against the variant, particularly after two doses. Delta, first identified in India, has since spread to at least 85 countries, including the U.S., where it is now estimated to be the most common variant.

The U.K. is a testing ground for how vaccines are coping. Delta is racing through the country—with 146,000 identified cases in the past week, 72% up on the week before. The country is also a world leader in identifying through testing and genetic sequencing which versions of the virus are prevalent: By mid-June, 97% of cases were Delta infections. And Delta is spreading among a population that is among the most highly vaccinated in the world: 85% of adults have had at least one vaccine shot and 63% have had two.

The spread of Delta has led the U.K. government to postpone by a month the ending of Covid restrictions until July 19. But ministers are increasingly confident that the unlocking will take place as planned because vaccinations have broken the lockstep between new cases, later hospitalizations and deaths.

Data from Public Health England show that there were 117 deaths among 92,000 Delta cases logged through June 21. Fifty of those—46%—had received two shots of vaccine.

But rather than suggest Delta is displaying a worrying ability to evade the vaccine and cause severe illness, scientists say those figures support the shots’ effectiveness. There are three main reasons why.

First, vaccines aren’t 100% effective. Not everyone who is inoculated will respond in the same way. Those who are elderly or whose immune systems are faulty, damaged or stressed by some other illness are less likely to mount a robust response than someone younger and fitter. Covid-19 vaccines are highly effective but some people will still be vulnerable to the virus even after receiving their shots.

Second, the risk of dying from Covid-19 increases steeply with age. If a vaccine reduces an 80-year-old’s risk of death from Covid-19 by 95%, for instance, that 80-year-old’s risk of death might still be greater than the risk faced by an unvaccinated 20-year-old. Some chronic illnesses such as diabetes, hypertension and lung disease are also associated with a higher risk of severe illness and death.

Third, as more of the population gets vaccinated, there are fewer unvaccinated people for the virus to infect. If the pool of vaccinated people is larger than the pool of unvaccinated people, then it is possible and even likely that breakthrough infections resulting in death in the older, vaccinated group would match or exceed deaths in the younger, unvaccinated group. Consider an imaginary country with 100% of people vaccinated, where the virus can still somehow spread. All Covid-19 deaths would be in vaccinated individuals.

Of those 50 deaths in fully vaccinated people in England, all were in people aged 50 years and over, the data show. There have been no deaths recorded in double-vaccinated under 50s.

The data show that, overall, the fatality rate for confirmed cases of Covid-19 has been lower than it was with the Alpha variant, which was first spotted in the U.K. late last year and has since spread around the world. Public Health England pegged the fatality rate for Alpha at 1.9%. It estimates the fatality rate for Delta is closer to 0.3%, which scientists say reflects both mass vaccination and improved treatment for Covid-19. And the vaccine also reduces the chances of catching the virus at all.

Tom Wingfield, a lecturer and infectious-disease physician in Liverpool, England, said these effects are visible in the Covid-19 wards in his district during the current Delta-fueled wave of infection in the U.K.

Those requiring hospital treatment are far fewer in number than in previous waves, he said. So far, the majority have been unvaccinated. Most are from younger age groups who have only recently been made eligible for shots and tend to need less intensive treatment than older patients.

Dr. Wingfield said he has seen Covid-19 patients who have had their shots, but that they have tended to be frail and elderly or suffering from chronic illness. Healthier people who have been double dosed are much less common, he said.

“I think it shows the vaccines are working,” Dr. Wingfield said.

Irene Petersen, professor of epidemiology and health informatics at University College London, said by using a simple, back-of-the-envelope calculation, it is possible to estimate the number of people who might have died in the absence of vaccines in this current phase of the pandemic.

The data show there were 59 over-50s among the 117 deaths who hadn’t received two vaccine doses. Assuming a take-up rate of the vaccine of 95%, in line with the rates seen among the oldest age groups in Britain, that implies some 1,180 people might have died from Covid-19 in the absence of vaccination. Ninety-five percent of that number—1,121—would have occurred in those who are now fully protected. Since only 50 deaths occurred in that group, that implies vaccines reduced the risk of death by 95%.

Public Health England, using a variety of statistical analyses, has estimated that vaccination reduces the risk of hospitalization with the Delta variant in people who have received two doses by between 91% and 98%, with a central estimate of 96%.

Though vaccines offer substantial protection against severe illness and death, there is growing evidence from lab studies and real-world data that Delta does have some ability to bypass vaccines to cause milder infection.

Public Health England says that its analysis of Delta cases in England implies protection against symptomatic Covid-19 caused by Delta of around 79%. That compares with an 89% reduction in the risk of symptomatic Covid-19 with Alpha.

In Israel, a senior health official said in late June that in a recent outbreak of 200 or so Delta cases, about half were in children 15 years old and younger and the other half were in those aged 16 and above, of whom more than 80% are fully vaccinated.

British data shows Delta is even more adept at evading our immune response after just one dose of vaccine, highlighting the importance, public health officials say, of getting two shots. A single dose reduces the risk of symptomatic Covid-19 with Alpha by 49%, according Public Health England, but only by 35% with Delta.

“What the U.K. is seeing now is increasing coverage of the vaccine does actually suppress the need for hospitalizations, and deaths, from the Delta variant. But there are breakthrough infections,” said Julian Tang, a clinical virologist and professor of respiratory medicine at the University of Leicester.

Write to Jason Douglas at jason.douglas@wsj.com and Stephen Fidler at stephen.fidler@wsj.com

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