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WASHINGTON -- COVID booster shots are showing good efficacy in Israel, Anthony Fauci, MD, chief medical advisor to President Biden, said Thursday at a briefing held by the White House COVID-19 Response Team.

Researchers have found that, even with the country's very high vaccination rate, "we see new PCR-positive infections and new severe COVID cases in fully vaccinated people during the Delta wave in Israel from June 1 up to August 1. So clearly, Delta is dominant, and is responsible for new cases, including severe disease," said Fauci, who is also director of the NIAID.

Booster Clearly Helped

A third dose of the Pfizer-BioNTech vaccine was approved in Israel for people age 60 and older. A total of 1.1 million people received that booster shot between July 30 and August 22, "and a rather substantial positive impact was seen," Fauci continued, referring to a by Yinon Bar-On, of the Weizmann Institute of Science, and colleagues published in MedRxiv.

"Twelve days or more after the booster dose, there was a greater than tenfold diminution in the relative risk of both confirmed infection and severe disease," Fauci said.

The chances of testing positive with two doses versus three doses of the Pfizer vaccine was looked at in published on MedRxiv by Tal Patalon, MD, of Maccabi Healthcare Services, and colleagues. In that study, among "more than 150,000 people in the first 3 weeks of August, they found after 7 to 13 days up to a 68% reduction in the risk of infection" if a third dose was given, Fauci said.

"And after 14 to 20 days, a 70% to 84% reduction in the risk of infection. There is no doubt from the dramatic data from the Israeli study that the boosts that are being now done there and contemplated here, support very strongly the rationale for such an approach."

During a question-and-answer session, Fauci was asked whether support in the U.S. for booster shots was sending a message to other wealthy nations encouraging them to keep their extra doses for boosters rather than donating them to other countries who need them.

"I'd hope the countries that are boosting their population similar to what we are understand the importance of the global necessity to essentially suppress this at a global level," Fauci said. "That's the reason why the United States is setting an example" by also donating hundreds of millions of doses to other countries.

Will "Fully Vaccinated" Soon Mean a Third Dose?

Fauci also was asked whether he expected the U.S. will eventually only consider people who have gotten that third booster dose to be fully vaccinated. That determination will be up to the FDA when they get the data on the three doses and the recommendation of the CDC's Advisory Committee on Immunization Practices, he said. "But I must say from my own experience as an immunologist, I would not at all be surprised that the adequate full regimen for vaccination will likely be three doses."

"The reason I say that is that it is very clear, when you give a prime and maybe a second shot as a boost, but give the immune system enough chance to mature in both affinity maturation and maturation of the B cell repertoire, it is entirely understandable why the results that I just reported from the Israeli boosters are so dramatic," he continued.

There's good reason to believe that the third dose generates a strong and durable response, he said. "And if it is durable, then you're going to have very likely a three-dose regimen being the routine regimen. But we'll just have to wait to make sure that that's the case, when the data get presented to the FDA."

Adolescent Vaccination

Also at the briefing, CDC Director Rochelle Walensky, MD, discussed COVID vaccine efficacy in adolescents. She said that two studies on that topic are coming in the MMWR on Friday.

"These studies compare pediatric cases, emergency room visits, and hospitalizations during the prior winter surge when vaccination rates were low, with this summer, when adult and adolescent vaccination coverages increased and the Delta variant is the dominant variant," she explained. "In both studies, one thing is clear: cases, emergency room visits, and hospitalizations are much lower among children in communities with higher vaccination rates. Vaccination works."

The first study analyzed data from hospitals in 99 counties across 14 states.

"The hospitalization rate among unvaccinated adolescents -- those aged 12 to 17 -- was nearly 10 times higher than that among fully vaccinated adolescents during the month of July," said Walensky. "The second study looked at national cases of emergency room visits and hospitalizations, and found that in August 2021, the rate of hospitalization for children was nearly four times higher in states with the lowest overall vaccination coverage, when compared to states with high overall vaccination coverage."

She acknowledged that "as cases were increasing throughout July and August, the number of children getting sick with COVID was also increasing. From late June and to mid-August, in the context of low community vaccination coverage and the rapid spread of the Delta variant, cases among children and adolescents 17 and under increased by nearly 10-fold, which aligns with the increase seen for the general population."

However, despite the increasing case numbers, she said, "these studies demonstrated that there was not increased disease severity in children. Instead, more children have COVID-19, because there is more disease in the community."

"What is clear from these data is community level vaccination coverage protects our children," she added. "As the number of COVID-19 cases increase in the community, the number of children presenting to the emergency room and being admitted to the hospital will also increase."

'Close Eye' on the Mu Variant

Briefing panelists also were asked about their thoughts on the "μ" (Mu) variant, which the WHO on Wednesday Fauci said that the administration is keeping "a very close eye" on the new variant. However, he added, "it is not at all even close to being dominant."

Although this variant "has a constellation of mutations that suggests that it would evade certain antibodies -- not only monoclonal antibodies but also vaccine- and convalescent serum-induced antibodies, there isn't a lot of clinical data to suggest that," Fauci said.

"It is mostly laboratory in vitro data ... But remember, even when you have variants that do diminish somewhat the efficacy of vaccines, the vaccines still are quite effective against variants of that type. Bottom line: we're paying attention to it, we take everything like that seriously, but we don't consider it an immediate threat right now."

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