A new report from the Centers for Disease Control and Prevention reveals that millions of Americans are not getting their second dose of the COVID-19 vaccine.

The report states that more than 5 million people, or 8% of those who got their first dose, missed their second dose of the Pfizer or Moderna vaccines.

Pharmacist Howard Jacobson says he's seeing some cancelations for second doses at his pharmacy in Rockville Centre.

Medical experts say there are several reasons a growing number of Americans are choosing not to receive the second dose. Some people have said they don't want to experience any potential side effects, while others feel like one shot is enough protection against the virus.

Another hurdle is vaccination sites running out of supply.

Dr. Maria Carney, of Northwell Health, says the trend is concerning because a single dose only provides partial protection against COVID-19.

She says a change in strategy may be in order to get more people vaccinated, and that instead of having people travel to remote locations such as Jones Beach and pharmacies, bring the shots to them at residential centers, schools and work places.

While a three or four-week gap between shots is ideal, the CDC says you can get your second shot within 42 days of the first one and still have a full immune response.