White House officials on Tuesday acknowledged the United States is likely to miss President Joe Biden's goal of having 70% of American adults partially vaccinated by July 4, as experts express concern about the potential of the delta coronavirus variant to cause Covid-19 outbreaks among the unvaccinated.

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US to miss Biden's goal

During a press conference Tuesday, Jeffrey Zients, the White House pandemic response coordinator, announced that more than 70% of adults ages 30 and over have received at least one shot of a Covid-19 vaccine, and 70% of adults ages 27 and over are likely to be partially vaccinated by July 4. However, the United States won't meet President Biden's goal of having at least 70% of American adults partially vaccinated by July 4.

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According to a New York Times analysis, if vaccination rates continue at their current pace, around 67% of adults will be partially vaccinated by July 4.

Zients argued that missing Biden's goal by a few points isn't significant in light of the progress the United States has made in its vaccination effort.

"We have built an unparalleled, first-of-its-kind, nationwide vaccination program," Zients said. "This is a remarkable achievement."

"At the pace the U.S. was vaccinated before the president took office, it would have taken 336 days—almost a year—to get 300 million shots in arms," Zients added. "Instead of hitting the major milestone of 300 million shots in June, we would have hit it in December. … Let's remember when the president took office, we were at approximately 5% of adults with one shot. So in just five months we've been racing from 5% to 70%."

According to Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, 16 states and Washington, D.C. have vaccinated more than 70% of their adults, while four states have vaccinated less than 50%.

Experts express concern about delta variant

The announcement comes as experts continue to express concern over the potential that the delta coronavirus variant will cause Covid-19 outbreaks among the unvaccinated.

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"The delta variant is currently the greatest threat in the U.S. to our attempt to eliminate Covid-19," Fauci said.

According to Fauci, the delta variant was responsible for just 1.2% of Covid-19 cases on May 8, but as of June 19, that share had grown to 20.6%. That suggests the United States is following a similar pattern to what was seen in the United Kingdom, Fauci said, where the delta variant is now responsible for "well over 95%" of new Covid-19 cases.

However, Covid-19 vaccines do provide protection against the delta variant. "Two weeks after the second dose, the Pfizer-BioNTech (vaccine) was 88% effective against the delta variant and 93% effective against the alpha variant when you're dealing with symptomatic disease," Fauci said.

Because a significant share of the U.S. population is now vaccinated, it's unlikely the country will see a widespread resurgence in Covid-19 cases, according to Justin Lessler, an epidemiologist at Johns Hopkins University—but local outbreaks are still possible.

"We're not having massive epidemics at a national level, but we have this kind of continuation of the virus just sticking around and keeping us on our toes," he said. "And is specific places, there could be substantial epidemics still" (Fernandez, Axios, 6/22; LaFraniere, New York Times, 6/22; Frieden, MedPage Today, 6/22; Stein, "Shots," NPR, 6/22; Guzman, The Hill, 6/22; Miller, NBC News, 6/22; Miller, Associated Press, 6/22).