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Which COVID vaccine is the most effective against the delta variant?

Which COVID vaccine is the most effective against the delta variant?
Photo via Marco Verch/Flickr (CC BY 2.0)

With the delta variant causing COVID-19 cases to skyrocket across the country, breakthrough infections are being reported among even the fully vaccinated. Booster shots are just over the horizon, but some people may be starting to wonder which COVID vaccine currently on the market is the most effective at fighting the highly transmissible delta variant.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CBS News’ Face the Nation on Aug. 15, that all of the current vaccines are effective at preventing severe disease, hospitalizations, and deaths from the delta variant.

The Pfizer and Moderna vaccines initially provided 95% and 94.1% protection, respectively, against COVID-19. The Johnson & Johnson vaccine, which is 85% effective against the disease’s most serious symptoms, is still being studied to determine when booster shots may be needed. More data is expected within the coming weeks.

“We certainly are getting what are called breakthrough infections, which means a person who was vaccinated might get infected and actually may even spread the virus,” Fauci said. “But in general, those people are not the ones who are getting seriously ill and dying. It’s the unvaccinated that are doing that.”

During his appearance, Fauci was also asked about a new study out of Minnesota that suggests the Moderna vaccine is more effective against the delta variant than the Pfizer vaccine. This sparked questions about whether, assuming the study is accurate, people who got Pfizer the first time around should get a Moderna booster shot?.

In response to these questions, Fauci advised in no uncertain terms against mixing and matching COVID-19 vaccines.

“That study, first of all, is a pre-print study; it hasn’t been fully peer-reviewed,” said Fauci. “I don’t doubt what they’re seeing, but there are a lot of confounding variables in there about when one was started, the relative amount of people in that cohort, that’s delta versus alpha.”

“Right now, if we get boosters, you know, we’re talking about boosters,” he continued. “We already implemented boosters for the immune-compromised. It’s clear we want to make sure we get people, if possible, to get the boost from the original vaccine that they had.”

Fauci also pointed out that the initial dose of Moderna is about three times Pfizer’s dose, which is another reason why switching vaccines is ill-advised.

“So you may have a difference in durability,” added Fauci. “But in general, the vaccines that have been approved for emergency use authorization and hopefully will be approved for a full authorization in the sense of actual approval, hopefully, that comes very soon are all really highly effective in preventing severe disease.”

The Pfizer vaccine was granted full approval from the U.S. Food and Drug Administration on Aug. 23.

Even though mixing vaccines and boosters are discouraged, it’s important to note that booster shots will likely eventually be necessary for lasting protection from the virus.

Just a few days before the Pfizer vaccine received full approval, the Centers for Disease Control and Prevention published three studies that suggested protection from vaccines declined over the summer as the delta variant rose to become the dominant strain of the virus.

One of the studies conducted in New York found that effectiveness from vaccines dropped from 92% in May to 80% in late July.

“Examining numerous cohorts through the end of July and early August, three points are now very clear,” CDC director Rochelle Walensky said during an Aug. 18 White House press briefing. “First, vaccine-induced protection against infection begins to decrease over time. Second, vaccine effectiveness against severe disease, hospitalization, and death remains relatively high. And third, vaccine effectiveness is generally decreased against the delta variant.”
Sources: CBS News, Washington Post, White House


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