(WKOW/CNN) -- The CDC says about eight percent of Americans have missed their second dose of the COVID-19 vaccine.
The agency says the number is up from about 3.4 percent back in March.
The numbers don't take into account the people get their first dose at one clinic, but got their second shot at a different clinic.
The World Health Organization has said it's safe to give doses of Pfizer/BioNTech's vaccine as far apart as six weeks.
However, US federal vaccine advisers say it's best for people to stay as close to the three week schedule as possible.