ATLANTA — Georgia threw open the doors for COVID-19 vaccination to a majority of adults, as the state seeks to improve its worst-in-the-nation share of the population that has been inoculated against the respiratory illness.

Monday was the first day that people aged 55 to 64 could get shots, as well as people with serious health conditions and those who are overweight and obese.

Officials with Gov. Brian Kemp’s office say that, overall, another 3.3 million people are eligible, meaning more than 5 million Georgians overall can now seek vaccination.

The state will open five new mass vaccination sites on Wednesday and the federal government will take over a site in Atlanta.

Georgia has only given 20.8% of its adult population at least one dose, the worst in the nation, according to the U.S. Centers for Disease Control and Prevention. The same data show Georgia has administered the second-lowest share of doses delivered among states, with more than one-third of doses still awaiting injection.