Health care workers and residents of long-term care facilities should be first in line when COVID-19 vaccines are authorized by the Food and Drug Administration (FDA), which could happen in a matter of weeks, according to a Centers for Disease Control and Prevention (CDC) advisory committee.

Members of the Advisory Committee on Immunization Practices (ACIP) voted 13 to 1 to prioritize these two high-risk groups, which together include around 24 million Americans. Health care workers and people in congregate living facilities, such as nursing homes, are at high risk for exposure to the new coronavirus, and older people have a greater likelihood of developing severe COVID-19 and dying from it. Nursing home residents and staff account for some 40% of COVID-19 deaths in the United States.

CDC director Robert Redfield, MD, has accepted the recommendation, according to the ACIP website. However, states and local jurisdictions will make the final decisions about vaccine prioritization.

The next phase of vaccine distribution will include other essential workers, such as teachers, police and firefighters, grocery workers and public transit workers. The third phase will include people over age 65 and those with underlying health conditions that put them at risk for severe COVID-19, such as diabetes and obesity. Although prisons have seen large COVID-19 outbreaks, the committee did not prioritize incarcerated people.

The ACIP vote came at an emergency meeting on December 1, which was conducted virtually and open to the public. The following day, the Medicines and Healthcare Products Regulatory Agency (MHRA)—the FDA’s counterpart in the United Kingdom—granted emergency authorization for Pfizer and BioNTech’s mRNA vaccine. Prime Minister Boris Johnson announced that a mass vaccination campaign will start next week. The first shipment of 800,000 doses, manufactured in Belgium, will be distributed to 50 hospital hubs that can store them at super-cold temperatures, The Guardian reports. In the United Kingdom, care home residents and staff, people over age 80 and health care workers will be vaccinated first.

The FDA conducts a more thorough review than the MHRA, one that involves delving into the raw vaccine trial data provided by the pharmaceutical companies. The FDA’s Vaccines and Related Biological Products Advisory Committee will meet on December 10 to discuss the Pfizer/BioNTech vaccine and again on December 17 to discuss another vaccine from Moderna and the National Institutes of Health (NIH).

The Pfizer/BioNTech vaccine was 95% effective, and the Moderna/NIH vaccine, which uses a similar mRNA approach, was 94% effective in preventing symptomatic COVID-19 in Phase III clinical trials, the companies announced. Both vaccines worked well across sex and racial/ethnic and age groups, including people over 65. A third vaccine, from AstraZeneca and the University of Oxford, which uses an adenovirus vector approach, also appears to be highly effective, though questions remain about dosing regimens and the lack of older volunteers in the group that received the most effective regimen.

If the Pfizer/BioNTech vaccine receives FDA emergency use authorization shortly after the December 10 meeting, distribution could begin immediately, potentially followed by the Moderna/NIH vaccine a week later. Operation Warp Speed has underwritten the production of millions of doses even before the vaccines are approved.

Operation Warp Speed chief scientific adviser Moncef Slaoui, MD, has predicted that 20 million Americans could receive vaccines by the end of the year and about 100 million—including health care workers, other essential workers, older people and those with underlying health conditions—could be vaccinated by the end of February. 

Most experts expect that vaccination for the rest of the adult population is likely to start around April, though they disagree about how long it will take before everyone who wants a vaccine can get one. Slaoui predicts that the entire U.S. population could be vaccinated by June and the rest of the world by early to mid-2022, CNBC reports. Others think it will take longer. The vaccines have not yet been tested in children, though studies in teens are expected to start soon.

The Pfizer/BioNTech and Moderna/NIH vaccines each require two shots, spaced three to four weeks apart, and it is expected to take another couple of weeks to develop full immunity. Distribution could speed up if additional vaccines are approved—especially single-shot candidates—but it could be hampered by hesitancy about vaccination.

It is still unclear whether these vaccines prevent coronavirus infection and transmission in addition to symptomatic illness or how long immunity might last. It will still be important to take precautions, such as wearing masks and social distancing, until this is determined and a large proportion of the population is vaccinated.

Nonetheless, many experts are optimistic.

“If we get 60% to 70% of people vaccinated with a vaccine that’s more than 90% effective, we probably will reach a point that’s pretty close to herd immunity, where the virus just can’t find enough mouths and noses that aren’t immune,” Bob Wachter, MD, of the University of California at San Francisco, told COVID Health. “It’s reasonable to expect that by next summer, we’ll be in pretty good shape.”