FDA Deems Plans to Spread Out COVID-19 Vaccine Doses 'Premature'

Flatlay on a blue background of syringes and vaccine vials that say COVID-19

Yulia Reznikov/Getty


On Friday, January 8 the World Health Organization (WHO) approved delaying the times between doses of Pfizer and BioNTech’s COVID-19 vaccine. They published guidance stating that the interval between both doses can be extended up to 42 days (6 weeks), based on clinical trial data. The recommended interval is still 21 to 28 days, and the U.S. has not yet announced plans to extend the time between doses.

Key Takeaways

  • The United Kingdom and some parts of Canada have released plans to space out the second doses of the COVID-19 vaccines.
  • The goal of the controversial step is to at least partially vaccinate as many high-risk patients as possible in a short period of time.
  • Health officials in the United States are warning against taking a similar approach.

Health officials in the United Kingdom have released a controversial plan to delay the recommended second doses of the Pfizer and AstraZeneca COVID-19 vaccines in an attempt to vaccinate as many high-risk people as possible in a short period of time. While health officials elsewhere in the world are considering similar tactics, on Monday, the Food and Drug Administration said there is not enough evidence to pursue a change in the dosing schedules in the U.S. at this time.

In a statement posted online on December 30, 2020, the U.K.'s Department of Health and Social Care said that the country’s Joint Committee on Vaccination and Immunisation (JCVI) will focus on giving at-risk people their first dose of the Pfizer/BioNTech and Oxford University/AstraZeneca vaccines “rather than providing the required two doses in as short a time as possible.”

The statement says that “everyone will still receive their second dose and this will be within 12 weeks of their first. The second dose completes the course and is important for longer-term protection.”

COVID-19 Vaccine Basics

Currently, there are two COVID-19 vaccines approved for use in the U.S.: the Pfizer/BioNTech vaccine and the Moderna vaccine.

Both vaccines use a newer technology called messenger RNA (mRNA). These vaccines work by encoding a part of the spike protein on the surface of SARS-CoV-2 (the virus that causes COVID-19).

The mRNA vaccines use pieces of the encoded protein to create an immune response and the body develops antibodies to SARS-CoV-2. Eventually, the body eliminates the protein and mRNA, but the antibodies remain. 

The Oxford University/AstraZeneca vaccine, which is approved for use in the U.K., uses a genetically engineered adenovirus—a type of virus that can cause colds and other infections. The altered virus carries a gene for a coronavirus protein that is designed to train the body to recognize and fight SARS-CoV-2.

Why You Need Two Shots

Research on both vaccines has shown that they are most effective when two doses are given.

Stanley Weiss, MD

It’s usually wise in medicine to try to follow administration of any vaccine or drug in the same manner it was studied.

— Stanley Weiss, MD

Stanley Weiss, MD, professor at the Rutgers New Jersey Medical School and the Department of Epidemiology at the Rutgers School of Public Health, tells Verywell that the first dose helps your body learn to recognize the virus and primes your immune system for dealing with future infections. The second shot makes your body’s immune response stronger.

Going Against Current Recommendations

Pfizer/BioNTech currently recommends that the two doses of its vaccine be given three weeks apart. The two doses of the Oxford University/AstraZeneca vaccine are to be given 28 days apart.

The JCVI states that the goal of spacing out the doses in the U.K. is to “vaccinate a greater number of people who are at highest risk, protecting them from the disease and reducing mortality and hospitalization.”

The group also says that the approach “will maximize the benefits of both vaccines,” and "will ensure that more at-risk people are able to get meaningful protection from a vaccine in the coming weeks and months, reducing deaths and starting to ease pressure on” the country’s healthcare system.

What Global Experts Say

The British Medical Association (BMA) has spoken out against the recommendation, calling it “grossly unfair” to at-risk people. In a statement, the BMA said that asking general practitioners to “rebook appointments of tens of thousands of elderly and vulnerable patients due to get their second dose of the COVID-19 vaccination in a few days’ time, is unreasonable and totally unfair, and practices who honor existing appointments booked for the next few days should be supported."

The BMA also reported that it has heard from “scores” of medical practitioners and leaders who say that delaying full vaccination “will have a terrible impact on the emotional well-being of their most vulnerable, at-risk patients.”

The association is also concerned about the logistics of rebooking patients which can “cause huge logistical problems for almost all vaccination sites and practices.”

What U.S. Experts Say

Some top health officials in the U.S. have also spoken out against delaying a second dose of the vaccine. “I would not be in favor of that,” Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, told CNN. “We’re going to keep doing what we’re doing.”

In an interview with Face the Nation on Sunday, Moncef Slaoui, PhD, scientific adviser of Operation Warp Speed, said that the U.S. is considering giving some people two half-doses of 50 micrograms each of the Moderna vaccine to try to get more immunity from the country’s limited vaccine supply. “We know it induces identical immune response to the 100-microgram dose," Slaoui said, "And therefore we are in discussion with Moderna and with the FDA."

Pushback from the FDA

The FDA has pushed back. FDA Commissioner Stephen Hahn, MD and Peter Marks, PhD (who leads the FDA's Center for Biologics Evaluation and Research overseeing vaccine safety), said in a statement Monday that they "have been following the discussions and news reports about reducing the number of doses, extending the length of time between doses, changing the dose (half-dose), or mixing and matching vaccines in order to immunize more people against COVID-19."

Stanley Weiss, MD

It’s a public relations nightmare to change the vaccine schedule at this time.

— Stanley Weiss, MD

Hahn and Marks said that while the questions are reasonable to consider and evaluate through clinical trials, at this time, "suggesting changes to the FDA-authorized dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence."

In the absence of data supporting making changes to vaccine administration, Hanh and Marks said that it doing so could place public health at risk and undermine "the historic vaccination efforts to protect the population from COVID-19."

Evidence, Efficacy, and Public Perception

Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, tells Verywell that he also has concerns about what altering the vaccine plan would be mean for its effectiveness. “If you stretch out or lower doses, there is a concern that the efficacy will be different or less durable,” Russo says." It’s biologically plausible that people will probably be OK if they get the second vaccine later, but it hasn’t been studied.”

Weiss agrees that we should stick with vaccine administration recommendations that are based on clinical trial data rather than altering the duration. “Right now, we’re giving the vaccine to people who are at very high risk of exposure, such as healthcare workers and the elderly," Weiss says. "Having very high efficacy is really important to give them adequate protection.

Weiss adds that the data is also based on a two-dose regimen given during a certain schedule. “It’s usually wise in medicine to try to follow administration of any vaccine or drug in the same manner it was studied."

Public perception is another concern. “We have an uphill battle in the U.S. in terms of getting people vaccinated,” Weiss says. “Altering the schedule or dosing could interfere with public perception and people wanting to get the vaccine. It’s a public relations nightmare to change the vaccine schedule at this time.”

What This Means For You

Health officials in the U.K. are spacing out COVID-19 vaccinations in an effort to vaccinate as many high-risk people as possible in a short period of time. While public health officials elsewhere in the world are considering similar plans, the U.S. is currently pushing back against delaying second doses.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Department of Health and Social Care. Oxford University/AstraZeneca vaccine authorised by UK medicines regulator.

  2. Centers for Disease Control and Prevention (CDC). Understanding mRNA COVID-19 vaccines.

  3. Pfizer. Pfizer and BioNTech Choose lead mRNA vaccine candidate against COVID-19 and commence pivotal phase 2/3 global study.

  4. Knoll MD, Wonodi C. Oxford–AstraZeneca COVID-19 vaccine efficacyThe Lancet. Published online December 2020. doi:10.1016/s0140-6736(20)32623-4

  5. British Medical Association. BMA says decision to delay follow-up dose of Pfizer vaccine ‘grossly unfair’ to thousands of at-risk patients in England, as appointments are rescheduled.

  6. CBS News. Transcript: Moncef Slaoui on "Face the Nation,"

  7. FDA. FDA statement on following the authorized dosing schedules for COVID-19 vaccines.

By Korin Miller
Korin Miller is a health and lifestyle journalist who has been published in The Washington Post, Prevention, SELF, Women's Health, The Bump, and Yahoo, among other outlets.