Opinion | How Dangerous Is the Delta Variant?

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When a wave of coronavirus infections crashed over India in the spring, scientists wondered whether a new variant, Delta, was partly to blame. Time appears to have answered the question: Having spread to at least 85 countries, the Delta variant is now fueling outbreaks around the world and prompting new lockdowns — even in countries that seemed to have the virus under control.

“The Delta variant is currently the greatest threat in the U.S. to our attempt to eliminate Covid-19,” Dr. Anthony Fauci said last week.

What makes the Delta variant so concerning, and how will it affect the course of the pandemic? Here’s what people are saying.

What scientists know about the variant so far

The Delta variant has multiple mutations that appear to make it 40 to 60 percent more transmissible than Alpha, the variant first identified in Britain, which is itself estimated to be about 30 to 50 percent more transmissible than the original coronavirus. In Australia, security cameras even documented a transmission that occurred between two people passing each other in a shopping mall.

“It is the most hypertransmissible, contagious version of the virus we’ve seen to date, for sure — it’s a superspreader strain if there ever was one,” Eric Topol, a professor of molecular medicine and an executive vice president at the Scripps Research Institution, told Scientific American.

The good news: Several of the vaccines in use still appear to work well against Delta.

A Public Health England study published in May found that the variant only slightly reduced the effectiveness of two doses of the Pfizer and AstraZeneca vaccines. The Moderna vaccine is expected to perform similarly well.

A preprint from Public Health England found that two doses of either vaccine also provided exceptional protection against hospitalization from the Delta variant.

But: The Delta variant does seem to pose a greater risk to people who have received only one dose.

According to Public Health England, a single dose of either AstraZeneca’s or Pfizer’s vaccine reduced a person’s risk of developing Covid-19 symptoms by 33 percent, compared with 50 percent for the Alpha variant.

A single dose of AstraZeneca showed reduced protection against hospitalization. (There was no major difference with Pfizer.)

Preliminary evidence also suggests that the two Chinese vaccines, Sinovac and Sinopharm, may be less effective against Delta. Those vaccines are being used in more than 90 countries, including the Seychelles, Chile, Bahrain and Mongolia, which have all outpaced the U.S. vaccination rate. All four ranked among the top 10 countries with the worst Covid outbreaks as recently as last week. “If the vaccines are sufficiently good, we should not see this pattern,” said Jin Dongyan, a virologist at the University of Hong Kong.

What scientists don’t know

Whether the Delta variant causes more severe illness than other variants remains an open question. One Scottish study published in The Lancet found that the hospitalization rate of patients was about 85 percent higher than that of patients with the Alpha variant. But virulence is a difficult trait to measure, as Katherine Wu explains in The Atlantic, and any one study should be taken with a grain of salt: “If a surge in virulence happens, it’s often incidental — collateral damage from an increase in contagiousness,” she writes.

It is also not yet known how effective the Johnson & Johnson vaccine is against the Delta variant, though studies are in progress. “Generally people are agreeing that they anticipate that J&J will perform well against the Delta variant as it has so far against other variants circulating in the United States,” said Dr. Rochelle P. Walensky, the director of the Centers for Disease Control and Prevention.

Yet others say it may be time for people who received the Johnson & Johnson vaccine to consider supplementing their protection with a dose of Pfizer or Moderna — an idea the C.D.C. and the F.D.A. have not yet weighed in on. “I just decided that it was a good idea for me to get a boost,” Angela Rasmussen, a virologist at the University of Saskatchewan, told Slate. “We know that at least two doses of an adenovirus vector vaccine and an mRNA vaccine provide protection equivalent to having two mRNA vaccines.”

The danger of Delta

Many experts are concerned by Delta’s contagiousness, regardless of whether it causes more severe disease. “In unvaccinated populations, experts generally have greater fears about more transmissible variants than ones that are, say, just deadlier, because by causing more cases than would have occurred otherwise, the faster spreading strains can result in greater hospitalizations and deaths overall,” Andrew Joseph writes in Stat. “Delta appears to be able to do that and more.”

Health care systems may strain even in places where vaccination rates are relatively high. In Britain, for example, where about half the population is fully vaccinated and the variant accounts for 90 percent of new infections, cases have increased sixfold in recent weeks. “What we’re seeing in U.K. is very likely to show up in other Western countries soon,” The Financial Times’s John Burn-Murdoch predicted at the end of May.

He was right. At the beginning of June, the Delta variant was responsible for 6 percent of U.S. infections. Now, it has overtaken the Alpha variant and is expected to account for a majority of infections by mid-July. Already, The Washington Post reports, it appears to be taxing hospitals in a lightly vaccinated part of Missouri, and hospitalizations are rising in Arkansas, Nevada and Utah, where less than 50 percent of the eligible population has received at least one vaccine dose.

By far the biggest risk, though, is to countries that have limited access to vaccines, Ewen Callaway writes in Nature. Experts are especially concerned about the potential for spread in Africa, where most nations have vaccinated less than 5 percent of their populations. Africa has weathered the pandemic much better than North America and Europe, but cases and deaths on the continent have increased by 40 percent in the past week.

“Many nations that excelled at protecting their citizens are now facing a triple threat,” Ed Yong writes in The Atlantic. “They controlled Covid-19 so well that they have little natural immunity; they don’t have access to vaccines; and they’re besieged by Delta.”

How to deal with Delta

The C.D.C. has given no indication that it plans to revise its guidance from May that fully vaccinated people can forgo masking in most situations, which paved the way for restrictions to be lifted across the country. But the W.H.O. disagrees, warning that while immunization is highly effective at preventing severe illness and death, the degree to which vaccines prevent transmission is unknown. In Los Angeles, the county reissued its indoor mask recommendation in part because of its large number of unvaccinated residents — particularly children, Black and Latino people and essential workers.

“Am I going to wear a mask among friends who are fully vaccinated? Probably not,” Gregg Gonsalves, a Yale epidemiologist, told The Times. “However, in public, I certainly will. This is about promoting a social norm: Right now there are enough people unvaccinated that we should be modeling good behavior, showing social solidarity.”

But others say that it is unrealistic to expect Americans to revert, so the goal should be getting more people vaccinated as quickly as possible. While staunch opposition to the vaccines remains a formidable obstacle to widespread immunity, “there’s still a big problem with people not having easy access,” Rasmussen told Scientific American. “We should start going door-to-door.”

And globally, democratizing vaccine access still remains the most urgent priority for containing the virus. “Vaccines that can save lives and turn this disease into a pre-pandemic baseline risk are available but in dire short supply,” says Zeynep Tufekci, a sociologist at the University of North Carolina, noting that even breakthrough infections from the Delta variant are overwhelmingly asymptomatic or mild. “Billions around the world deserve this. And there’s no time.”

Do you have a point of view we missed? Email us at [email protected]. Please note your name, age and location in your response, which may be included in the next newsletter.


“Human Behavior During the Pandemic Is More Important Than Any Covid Variant” [The New York Times]

“In China’s latest outbreak, doctors say the infected get sicker, faster.” [The New York Times]

“Will the Johnson & Johnson Vaccine Need a Boost Against the Delta Variant?” [New York]


Here’s what readers had to say about the last edition: Britney Spears and the last resort of mental health care.

Kristen: “I think you have under-emphasized the role insurance companies have played in making mental health services out of reach to most people. … If you have a child with mental health issues (and I do), it is almost impossible to find a therapist who will treat children and who will accept insurance. I don’t mean ‘who will accept one’s specific insurance plan,’ I mean any insurance at all. You pay $100 and up for a 30-minute session or you don’t get treatment. And unless you live in the city, try to find a psychiatrist who will treat children. There just aren’t any.”

Smita: “One perspective I was hoping you would discuss was that of the hundreds of thousands of families with loved ones whose mental illnesses are driving them to destroy themselves and are destroying their families in the process. … There should be some kind of middle ground, short of a conservatorship, in cases where someone is clearly not capable of caring for themselves, where parents can petition for access to doctors and medical records so they can be part of the treatment team. Of course, there would have to be safeguards to ensure that was not used in an abusive way.”

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