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Do COVID vaccines work against the delta variant? What to know as it spreads in US

·5 min read

The delta coronavirus variant, formerly known as B.1.617.2, is sparking outbreaks in vulnerable, mostly unvaccinated regions all over the world.

It has emerged as the most dominant version of the virus in the U.S., now making up about 83% of analyzed cases. Nearly two months ago, the delta variant comprised just 6% of sequenced cases.

The nation’s most recent seven-day average of new coronavirus cases jumped by about 53%, with hospitalizations (up 32%) and deaths (up 19%) also on a concerning rise, according to a Thursday White House COVID-19 briefing.

Evidence shows the variant is about 60% more contagious than previous versions of the virus, though estimates vary.

Doctors and scientists say the public’s greatest defense against the virus and its variants is vaccination. But how well do the COVID-19 shots prevent serious disease caused by the delta variant?

Here’s the latest data on each of the three vaccines authorized for emergency use in the U.S.

Pfizer-BioNTech vaccine

A study from Public Health England found that three weeks after one dose, the Pfizer-BioNTech vaccine was 33% effective against symptomatic COVID-19 caused by the delta variant. Two weeks following the second dose, which is recommended for full protection, it was 88% effective.

However, data from Israel shows the Pfizer vaccine’s effectiveness dropped to 64% in preventing infection and symptomatic illness as the country deals with the delta variant, which is the dominant version of the virus there.

Still, the shot remains 93% effective against serious COVID-19 and hospitalization.

Moderna vaccine

Results from a laboratory study released in June showed the Moderna COVID-19 vaccine appears effective against the delta variant, as well as other variants tested, with just a “modest reduction” in antibody levels compared to the original strain.

The analysis of blood samples from eight people collected one week after their second dose in the Phase 1 clinical trial found antibody levels were about twofold lower when put against the delta variant compared to the original coronavirus strain.

But experts say it’s important to keep in mind that antibodies aren’t the only defenses your immune system has to fight the coronavirus. There are other components such as memory B cells and T cells that play major virus killing roles, too, though these players are less understood in the context of COVID-19.

Johnson & Johnson vaccine

The one-dose Johnson & Johnson COVID-19 vaccine also spurred antibody activity against the delta variant, and “at an even higher level” compared to that of the beta variant first identified in South Africa.

In all, it was 85% effective against severe/critical disease and protected against hospitalization and death.

Though a newer non-peer reviewed study posted Monday found the delta variant, as well as a list of other variants spreading across the globe, led to a 3.2- to 4.9-fold decrease in the level of antibodies produced after vaccination with the Johnson & Johnson shot compared to D614G, a previous coronavirus strain.

The researchers say their findings highlight the benefits of a potential second shot following one dose of the Johnson & Johnson vaccine to “increase protection against the variants.”

“The message that we wanted to give was not that people shouldn’t get the J.&J vaccine, but we hope that in the future, it will be boosted with either another dose of J.&J or a boost with Pfizer or Moderna,” Nathaniel Landau, a virologist at New York University’s Grossman School of Medicine, who led the study, told the New York Times.

What about booster shots?

All companies behind the COVID-19 vaccines in the U.S. have said they are working on another version of their vaccine to act as a booster for either prolonged or more effective protection.

But federal health officials say they aren’t needed — at least not yet.

In a rare joint statement released July 8, the Centers for Disease Control and Prevention and the Food and Drug Administration said fully vaccinated Americans do not need a booster coronavirus shot “at this time.”

Their announcement came shortly after Pfizer and BioNTech said they’re developing an updated version of their vaccine designed to specifically target the delta variant and that they plan to start clinical trials in August if given “regulatory approvals.”

Dr. Anthony Fauci, the White House chief medical adviser, told CNN that COVID-19 booster shots “theoretically” could help protect vulnerable people but that the recommendations from the CDC and FDA are based on data and information currently available. But that “doesn’t mean we stop there,” he said.

“There are studies being done now, ongoing as we speak, about looking at the feasibility about if and when we should be boosting people,” Fauci told the outlet. “So this isn’t something we say ‘no we don’t need a boost right now, the story’s ended forever.’ No, there’s a lot of work going on to examine this in real time to see if we might need a boost.”

While the COVID-19 vaccines in the U.S. are effective enough against the delta variant now, experts say the more the coronavirus hops from one person to the next, the more chances it has to mutate into a version that could one day evade the shots’ defenses.

The World Health Organization suggested fully vaccinated people still wear face masks whenever possible, citing the delta variant’s increased transmissibility and risk of serious COVID-19. It has been found in at least 98 countries as of July 2.

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