Adolescents ages 12-15 have entered the pool of people eligible for COVID-19 vaccination in the United States. Following federal authorization of the Pfizer vaccine for people under the age of 16, states began vaccinating this younger age group on Thursday, May 13. 

While the Centers for Disease Control and Prevention (CDC) has not yet started reporting vaccination data specifically for this age group, we can already tell it’s making a difference. The rate of first doses administered is starting to steady. This comes after several weeks of sharp decline.

Prior to this new tier of eligibility, most people who wanted to get vaccinated had already received at least one dose. Accordingly, the country experienced—and is still experiencing—waning enthusiasm for COVID vaccinations among adults. And a safety-related pause of the Johnson & Johnson vaccine on April 13 didn’t help. 

But now, pending parental support, a new crop of people may be ready and willing to get vaccinated. (Verywell survey data shows 59% of parents say they’ll have their children get vaccinated; 25% aren’t sure, and 16% will not.) According to NPR, the expanded Pfizer authorization adds 17 million people to the total number of Americans eligible for vaccination. About 87% of the U.S. population can now be vaccinated—but only 47.7% have received at least one dose.

What Does This Mean For Herd Immunity

Only a little over half of eligible people have received a vaccine dose. It will take at least 70% of the total population getting fully vaccinated to achieve herd immunity, though some experts say it will never happen in the United States.

On a state level, Maine is closest to hitting the 70% mark, and is the first state to fully immunize more than half of its population.

Herd immunity predictions are constantly changing since they’re tied to how well vaccination efforts went in a given week. Based on data from this past week, Vermont, Hawaii, and New Hampshire may be the first states to approach herd immunity. Each is currently pacing to fully vaccinate 70% of their populations during the month of June.

Herd immunity is a complex calculation that relies on both past infections and number of people vaccinated. Because the World Health Organization emphasizes herd immunity should rely on vaccination and not disease exposure, for the sake of projections, our numbers focus on the time it will take to hit 70% through vaccination alone.

As a country, though, the rate of first-time vaccinations has not yet picked up enough to help us get back on a clear path to herd immunity. Earlier this month, the U.S. fell from a July prediction to August. As of May 19, that prediction is September.

There’s some good news, though. Older adults, who are at the highest risk for severe COVID-19, have collectively cleared the 70% threshold. As of May 19, 73% of the U.S. population age 65 and older is fully vaccinated.

Data by Amanda Morelli/Adrian Nesta