Emily Oster says parents of unvaccinated kids should start masking indoors again, and a pediatrician agrees

• Emily Oster said parents should wear masks indoors, even if they're vaccinated.
• Masking could slow the Delta variant's spread to kids, who are still at low risk of serious illness.
• Dr. Richard Seidman says parents should feel OK sending unvaccinated kids to school - with masks.

The economist Emily Oster, the data-driven pregnancy and parenting author who has spoken out in favor of school reopenings during the coronavirus pandemic, tweeted a thread arguing that parents of unvaccinated kids should wear masks in public to keep their children safe.

"If you are a vaccinated person, even if your friends/family/everyone you love are all vaccinated, it would be nice for other people if you masked in public indoor spaces in case you have a lot of virus," Oster wrote.

Oster was writing in response to new guidance from the Centers for Disease Control and Prevention for everyone - vaccinated or not - to wear masks indoors in public in parts of the US with relatively high rates of COVID-19 cases.

By the CDC's definition, that threshold has been reached in most of the US, as the Delta coronavirus variant has fueled spikes in COVID-19 cases across the country, especially in states and counties with low vaccination rates.

"A more contagious virus = higher kid infection too," Oster wrote, adding that "serious disease risk remains REALLY LOW" for kids.

Still, she said, wearing masks - even if you're vaccinated - adds an additional layer of protection for kids.

A pediatrician agrees that masking offers the greatest level of protection

Dr. Richard Seidman, a pediatrician who is the chief medical officer of L.A. Care Health Plan, agrees. Seidman, who has a master's in public health, pointed out that in Los Angeles County, 20% of COVID-19 cases recorded in June among those 16 or older were so-called breakthrough infections of fully vaccinated people.

Though these people were much less likely to develop serious illness than the unvaccinated, data suggests they can still pass the virus to others, including to unvaccinated kids. For that reason, Seidman says officials are right to advocate wearing masks indoors.

"The guidance now is clear: Indoor, vaccinated or not, masks are required," he told Insider.

Like Oster, Seidman emphasized that children were still at a low risk of contracting COVID-19, let alone having a severe case.

"Unvaccinated children are certainly at risk of getting infected," he said. "The good news is the data still show that young kids tend not to get serious illnesses."

Despite the more contagious Delta variant, Oster says schools should reopen

Oster turned to that lesser risk while arguing for schools to open even in places where cases are surging.

"The risk of serious illness in kids from COVID-19 remains extremely low," she tweeted. "Far lower than many other risks (RSV, drowning, cars). And the costs of isolation for kids are big."

Right now, children as young as 12 in the US are eligible to be vaccinated for COVID-19.

Seidman, who has 19-year-old twins, said if his kids were younger, he'd most likely feel comfortable sending them to school this year with precautions like masking and frequent testing.

"There are many advantages to returning to school," he said, adding that he'd recommend parents send their kids to school.

Vaccines are still being tested for use in young children but could be authorized for them this fall. Seidman said the most important thing parents could do to protect those too young to be vaccinated was to encourage friends, loved ones, and even teachers to get vaccinated.