Will vaccines work against Delta variant? Skepticism about Israeli report

The delta variant is highly contagious. Do Covid vaccines still protect against it? Experts say that if people are waiting for a "magical moment" to get vaccinated, this is it. NBC News

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How effective are the vaccines against the delta variant?

There are two ways to answer this question. One is by analyzing blood samples from people who have been fully vaccinated.

Scientists can take Covid-19 antibodies found in the blood and test them against variants. Several such independent lab studies (here and here, for example) found that the vaccines in use do, in fact, protect against the delta variant of SARS-CoV-2, as well as reduce hospitalizations. The studies are considered preliminary and haven't been peer-reviewed.

They also provide a limited picture of all the ways the immune system works against Covid-19, because they measure only antibody response. Certain cellular responses also play key roles. T cells, for example, help by killing infected cells and harnessing the power of other immune cells in the fight against viruses. Lab studies don't usually measure T-cell response.

The second — and maybe more important — way to determine vaccine effectiveness is by simply observing what's happening in the real world in real time.

"It's very hard to translate laboratory data into 'what's going to happen if I'm vaccinated and someone sneezes on me and spreads delta all over my face?'" said Dr. David Wohl, a professor of medicine in the infectious diseases division at the University of North Carolina at Chapel Hill, who runs UNC's vaccine clinics.

That's why it's important for scientists to look to places like the United Kingdom, where the delta variant accounts for nearly 100 percent of current Covid-19 cases. Despite having higher vaccination rates than the U.S. — 68 percent in the U.K. have had at least one dose, compared to just under 55 percent in the U.S. — cases are rising in the U.K.

"The only real difference between us and them is delta," Wohl said. "I'm really worried that what's going on in the U.K. is precisely what's going to happen here."

"If you're waiting for some magical moment" to get vaccinated, he said, "this is it."

Experts say reports from Israel about a drop in vaccine effectiveness against the delta variant are intriguing because the country vaccinated a majority of its population before the U.S. did, and it now faces a surge in variant-related cases. A recent study from Israel found that the Pfizer vaccine was just 64 percent effective in preventing symptomatic illness in fully vaccinated people.

At the same time, the report found that the vaccine was 93 percent effective at preventing hospitalizations and serious illness — a significant benefit, experts say.

"Maybe the vaccine isn't preventing the really mild cases. That's OK," Grabenstein said. "It is preventing the really severe infections, the things that we fear the most."

Experts have been skeptical about the report from Israel's Health Ministry, mainly because the study's authors neglected to provide many details about how they did their research and who participated. ...