Doctors and other clinicians were previously advised to avoid giving coronavirus vaccine within two weeks of any other vaccine. But Dr. Kate Woodworth of the CDC's birth defects division said Wednesday that advice has now changed, saying there is substantial data on the safety of the vaccines.

"Extensive experience with non-Covid-19 vaccines has demonstrated that immunogenicity," or the ability of a vaccine to provoke an immune response, "and adverse event profiles are generally similar when vaccines are administered simultaneously as when they are administered alone," Woodworth told a meeting of the CDC's Advisory Committee on Immunization Practices (ACIP).

She said the clinical considerations are being updated to say that Covid-19 and other vaccines can be administered "without regard to timing," including on the same day.

The change is important because many children remain behind on their regular vaccinations, as the pandemic shut down many non-emergency medical checkups. The two-week delay threatened to add another hurdle to getting people protected against Covid-19 as well as other diseases such as influenza, tetanus and HPV.

The American Academy of Pediatrics also said Wednesday it supports giving routine childhood vaccines together with coronavirus vaccines.

After some discussion among ACIP members concerned people might not fully understand the advice, the CDC added some language to its guidance to make it clear that the agency doesn't know whether people will be more likely to have a reaction if they get a Covid-19 vaccine close in time to other vaccines.

The announcement came shortly before the vaccine advisers voted unanimously to recommend use of the Pfizer/BioNTech vaccine in youths age 12 to 15. They voted 14-0 to recommend use of the vaccine, with one recusal.

"This is one more step to gaining immunity and bringing the pandemic closer to an end," said Dr. José Romero, who chairs ACIP and who is also the secretary of the Arkansas Department of Health. "We still need to vaccinate the rest of the world, but we have made significant steps and are on the road."

The recommendation comes a day after the US Food and Drug Administration decided to expand the emergency use authorization (EUA) of the Pfizer vaccine to people as young as 12. CDC Director Dr. Rochelle Walensky approved the recommendations Wednesday.

"Today, I adopted CDC's Advisory Committee on Immunization Practices' (ACIP) recommendation that endorsed the safety and effectiveness of the Pfizer-BioNTech COVID-19 vaccine and its use in 12- through 15-year-old adolescents," Walensky said in a statement.

"CDC now recommends that this vaccine be used among this population, and providers may begin vaccinating them right away," she added.

FDA greenlights Pfizer Covid-19 vaccine for adolescents 03:59

Though young people are less likely to be seriously affected by Covid-19, they can still be infected and spread it to others. The CDC estimates more than 22 million children ages 5 to 17 have been infected with coronavirus, CDC's Dr. Sara Oliver said Wednesday.

CVS announced Wednesday its pharmacies will begin administering Pfizer's vaccine Thursday in more than 5,600 locations nationwide, according to a statement from the company.

With so many older people vaccinated, children and teens are starting to make up a larger proportion of coronavirus cases now than earlier in the epidemic.

"In April, 9% of Covid-19 cases were aged 12-17 years, which actually represents a larger proportion of cases than adults 65 and older," Oliver told the ACIP meeting.

About 45% of adults in the United States are fully vaccinated, according to data from the CDC on Wednesday.

But in 15 states, more than half of adult residents are fully vaccinated. Those states are: Connecticut, Maine, Massachusetts, Vermont, New Mexico, New Jersey, Rhode Island, South Dakota, Hawaii, Maryland, New York, Minnesota, Wisconsin, Nebraska and Iowa.