Half of all Americans have now received at least 1 vaccine dose

Less than six months after the U.S. began distributing coronavirus vaccines, the U.S. Centers for Disease Control and Prevention announced Friday that half of the country's population has received at least one dose.

More than 166.4 million residents, or 50.1% of the U.S. population, have received one shot so far, CDC data showed. There are over 132 million Americans that are fully vaccinated, according to CDC data.

The milestone comes days after the CDC announced that half of all American adults over 18 were fully vaccinated.

The U.S. first authorized the Pfizer vaccine for use in December and later approved vaccines manufactured by Moderna and Johnson & Johnson.

The Pfizer and Moderna vaccines, which use mRNA technology, require two doses, while Johnson & Johnson's vaccine is only one shot.

Vaccines were at first limited to health care workers, first responders and the elderly, but by the middle of April the entire country opened up vaccinations to anyone over 16. The FDA approved the Pfizer vaccine for anyone over 12 in early May.

Children under 12 are not yet eligible for coronavirus vaccines.

Health experts have said the increase in vaccinated Americans in the last couple of weeks has likely led to the major drop in coronavirus cases and deaths throughout the country.

Still, leaders have warned that a decline in vaccine demand could affect that progress.

The seven-day average of daily doses administered in the U.S. has gone from a peak of 3.3 million on April 11 to 1.6 million on May 21, according to the CDC.

Federal and state leaders are encouraging all eligible Americans to set up an appointment to get their free shots as soon as possible to help decrease cases.

Anyone who needs help finding a COVID-19 vaccine appointment can log onto vaccines.gov.