The United States hit a new milestone Friday in the battle against COVID-19, surpassing 100 million people who have been fully vaccinated, health officials said.

“That's 100 million Americans with a sense of relief and peace of mind, knowing that after a long and hard year, they're protected from the virus, knowing their decision to get vaccinated protects not just themselves, but also protects their families, their friends and their communities,” Jeff Zients, White House COVID-19 coordinator, said during a news briefing. 

Thirty percent of the population is now fully vaccinated.

Nearly 144 million Americans, or 43.3% of the population, had received at least one vaccine dose as of Thursday, according to the Centers for Disease Control and Prevention. 

Zients also noted that the U.S. reached another milestone this week by distributing 300 million vaccine doses since the shots were authorized for emergency use by the Food and Drug Administration.

But now the U.S. is reaching a point where the pace of vaccinations is slowing, a sign that the country already has inoculated the majority of those most eager to receive the shots. Zients said the Biden administration is “increasingly focused on other groups that will take time to reach, and we expect the number of shots administered each day to moderate and fluctuate.”

“That said, we will continue to vaccinate millions of Americans each and every day,” he said, adding that a daily average of 2.6 million vaccine doses were administered in the past week.

Zients said reaching this stage in the country’s vaccination efforts was expected, but “I think what is unexpected is how fast we've gotten here.”

The number of fully vaccinated Americans could be even higher at this point, but the CDC estimated this week that more than 5 million people, or about 8% of those who received a first dose, have missed getting their second shot.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and President Joe Biden’s chief medical adviser, said that number is in line with what is seen with other multi-dose vaccines and far better than the 20-30% seen with a shingles two-shot vaccine.

Fauci on Friday tried to stress the benefits of people following through with receiving their second dose by citing various studies. Among them was a real-world Israeli study of the Pfizer/BioNTech vaccine that showed people were 46% protected from documented infections 14 to 20 days after the first dose, but 92% protected seven days after the second shot.

Federal health officials know they have work to do to assure the vaccine hesitant. Surgeon General Dr. Vivek Murthy said the Biden administration is working to improve Americans’ confidence in the vaccines, telling them that getting inoculated is urgent and important, and ensuring they have access to the shots.

“Our efforts are focused on mobilizing trusted messengers, which include doctors and nurses, faith leaders and family members to get information out to people,” Murthy said.

A CNN poll released Thursday found that 26% of adult Americans say they will not try to get vaccinated. 

The U.S. has recorded more than 32 million COVID-19 cases and 571,000 deaths since the start of the pandemic.

The country’s seven-day average for new infections is 52,500, down 16% from a week before. Deaths and hospitalizations are also on the decline.