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Delta variant ‘more likely’ than previous COVID strains to infect kids, Fauci says

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.Susan Walsh/Associated Press

The growing prevalence of the highly transmissible delta variant of the coronavirus is raising alarms about the risk to those who have not been vaccinated for COVID-19, especially to children under 12 who are not yet eligible.

The variant could cause infections to rise among the approximately 50 million children under the age of 12 in the United States, Dr. Anthony Fauci, the nation’s top infectious disease expert, said on Wednesday, though he cautioned that children were not uniquely susceptible to the variant.

“It isn’t that [children] are more susceptible, but this virus is a more transmissible virus,” Dr. Anthony Fauci said in an interview with CBS. “Therefore, children will more likely get infected with this than they would with the alpha variant.”

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Dr. Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital, said, “With delta being more transmissible than the original strain, this means that all people who are unvaccinated are at greater risk. There is no research I’m aware of that this applies more to children than to other age groups.”

Sax also explained why vaccines have not yet been cleared for use in children under the age of 12.

He said in an e-mail that children under 12 so “rarely get severely ill” that it was a “much trickier risk-benefit trade-off than for older adults. ... I’m expecting that the FDA will require full clinical trial safety and efficacy data, and ultimately approve via the usual pathway rather than the Emergency Use Authorization, so it could be some time.”

Dr. Shira Doron, an infectious disease physician at Tufts Medical Center, said higher vaccination rates will protect the entire population, including children.

“When you have a large proportion of the adult population vaccinated, as we do in Massachusetts, it protects the unvaccinated, including the children,” Doron said in an e-mail. “In areas of the country and the world with lower adult vaccination rates, as the prevalence of the delta variant increases, we may see bumps in cases and hospitalizations among the unvaccinated, including children.”

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During a White House COVID-19 briefing on Tuesday, Fauci said the transmissibility of the delta variant, which was first identified in India, is “unquestionably greater” than the original COVID-19 strain and the alpha variant. Experts have said the delta strain is 60 percent more transmissible than the alpha variant, which was initially identified in the United Kingdom.

“The delta variant is currently the greatest threat in the US to our attempt to eliminate COVID-19,” Fauci said Tuesday, while adding that the vaccines are effective against it.

The Pfizer vaccine was “88 percent effective against the delta and 93 percent effective against the alpha when you’re dealing with symptomatic disease,” Fauci said.

The contagious strain makes up about 20 percent of new infections in the US and is on track to become the dominant variant in some parts of the country, he said.

“It will be the dominant strain among those areas, those regions of the country where the vaccination rate is lower than we would like,” Fauci said during the CBS interview. “For those areas where you have a high vaccination rate, you’re not going to see that. Again, another powerful reason why we need to get vaccinated.”

Clinical trials by Pfizer and Moderna are currently underway to test the vaccines in children under 12. Pfizer is currently authorized for emergency use starting at age 12, while Moderna has been approved for people 18 and older.

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Amanda Kaufman can be reached at amanda.kaufman@globe.com. Follow her on Twitter @amandakauf1. Martin Finucane can be reached at martin.finucane@globe.com.