The federal government has announced that the Pfizer/BioNTech and Moderna coronavirus vaccines can now be administered to anyone ages 65 or older and those with underlying health conditions that put them at risk for more severe COVID-19. The vaccine supply remains limited, however, and there is currently not enough to go around.

To date, about 31 million doses of the two vaccines have been distributed to states, but less than half of these—around 12 million—have actually been administered, according to the Centers for Disease Control and Prevention (CDC) vaccine tracker. The vaccine regimens tested in clinical trials involve two doses administered three or four weeks apart.

Speaking at a January 12 news conference, Health Secretary Alex Azar urged states to open up vaccination to people 65 and older and adults of any age with health conditions. He added that the government would release all remaining vaccine doses it was holding, after President-elect Joe Biden vowed to do the same when he takes office.

But there’s a problem. As the Washington Post first reported, the federal government does not actually have a stockpile of extra vaccines. The supply that was initially being held in reserve for second shots has already been distributed. Many people who received their first dose soon after the vaccines were authorized in mid-December have now had their second dose. This revelation surprised—and outraged—state officials who had hoped to increase their supply.

Biden has set a goal of vaccinating 100 million people during his first 100 days in office, but that will require getting more shots into more arms at a faster pace. Incoming CDC director Rochelle Walensky, MD, MPH, says this is still possible, CNBC reports. “It will be a hefty lift, but we have enough to do that,” she told CBS’s Face the Nation on January 17. National Institutes of Health director Anthony Fauci, MD, who will be a chief medical adviser to Biden, agreed, telling NBC’s Meet the Press that the goal “is absolutely a doable thing.”

Expanded Eligibility

A CDC advisory committee developed a detailed vaccine prioritization scheme that put health care workers and residents of long-term care facilities first in line in Phase 1a, followed by people over 75 and frontline essential workers in Phase 1b. People ages 65 to 74, younger adults with underlying health conditions and other essential workers were put in Phase 1c, with the remaining adult population falling in Phase 2.

The committee aimed to balance competing goals, including reducing COVID-19 mortality, maintaining health care capacity, slowing coronavirus transmission, minimizing disruption to society and ensuring equity in vaccine distribution. Some experts urged prioritization of older people, who are at much higher risk for severe COVID-19 and death. Others favored frontline workers, a group that faces the greatest risk of coronavirus exposure and disproportionately includes hard-hit African Americans and Latinos.

States have the final say on how they allocate vaccines. Some, including Florida and Texas, opened vaccination to people over 65 early on, while others, like California, debated which frontline workers should go first. 

Azar’s announcement came amid a growing consensus that getting vaccines into the most arms as soon as possible is of utmost importance, especially given the detection of new mutated coronavirus variants that are more easily transmitted. 

To that end, more than half of states have broadened their criteria, with some setting up mass vaccination sites at sports stadiums, convention centers and even Disneyland in California.

But the expanded eligibility opens the door for what many see as misallocation. The CDC’s list of conditions that increase COVID-19 risk includes obesity, smoking, diabetes, cancer, compromised immunity and chronic heart, kidney or lung disease. So, for example, a young, otherwise healthy smoker would be competing with an 80-year-old with cancer. And people who can work from home could move ahead of those who must interact daily with the public.


The expanded prioritization means that some 100 million more people now qualify for vaccines while the supply remains limited, leading to long lines, lengthy waits to schedule appointments and a general sense of chaos and frustration.

Can the Second Dose Be Delayed?

Given the slow rollout of the vaccines, experts are discussing ways to speed up distribution, including delaying the second dose, giving two half doses and implementing a lottery system.

Results from the Phase III trials of the Pfizer/BioNTech and Moderna vaccines as well as the AstraZeneca/University of Oxford vaccine—which has been authorized in the United Kingdom but not yet in the United States—showed that they provide a high level of protection after the first dose.

The Pfizer/BioNTech and Moderna vaccine appear to be around 80% to 90% effective after the first shot, rising to 95% and 94%, respectively, after the second dose. What’s more, a recent modeling study indicated that a flexible dosing strategy for the Pfizer/BioNTech vaccine could potentially prevent an additional 25% of COVID-19 cases.

The second vaccine dose is expected to confer longer-lasting immunity, but it may not be crucial to give the booster on schedule three or four weeks after the first dose, as was done in the trials. In fact, the AstraZeneca/Oxford vaccine results suggest waiting longer might improve its effectiveness.

When the U.K. authorized the AstraZeneca/Oxford vaccine in late December, health officials announced that they would give twice as many people their first dose right away, deferring the second dose for up to 12 weeks.

It is not yet clear how long natural or vaccine-induced immunity against the coronavirus will persist, but most experts expect it will last at least a few months. Older people and those with a compromised immune system, who don’t respond as strongly to vaccines, may need both doses within a shorter time frame to achieve the full benefit.

“In a perfect world, there would be no trade-offs. But if 2020 taught us anything, it’s that we don’t live in a perfect world,” Bob Wachter, MD, of the University of California at San Francisco, and Ashish Jha, MD, MPH, of Brown University School of Public Health, wrote in a Washington Post opinion piece. “Between 50,000 and 100,000 Americans will die of COVID-19 this month alone. Giving 100 million people—particularly those at high risk—a single shot that is 80% to 90% effective will save far more lives than giving 50 million people two shots that are 95% effective. It’s what we should do.”

But other experts urge caution about deviating from the vaccine protocol tested in clinical trials, saying there is not yet enough evidence to support it. The Food and Drug Administration (FDA), the Infectious Diseases Society of America and the World Health Organization (WHO) all advise sticking to the original vaccination schedule, although the WHO said the dosing interval could be extended up to six weeks while supplies are limited.

[UPDATE: On January 21, the CDC updated its vaccine recommendations to advise that the second dose of the Pfizer/BioNTech and Moderna vaccines can be given up to six weeks after the first.]

“[A]t this time, suggesting changes to the FDA-authorized dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence,” Stephen Hahn, MD, and Peter Marks, MD, PhD, of the FDA, said in a statement. “Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19.”

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