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UK officials are allowing single doses of COVID-19 vaccines. SOPA Images/Getty Images
  • In the United Kingdom, a lack of COVID-19 vaccine doses has led health officials to announce that they’ll be distributing the vaccine in single doses to reach more of the population.
  • The FDA has warned against this type of vaccine plan.
  • We talked to experts about what they advise.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

The COVID-19 vaccine is here and will likely help stop the transmission of the novel coronavirus.

But there’s a big problem: There aren’t enough vaccine doses to go around.

The lack of doses is causing controversy in how it’s distributed both here and abroad.

In the United States, the Food and Drug Administration (FDA) has currently approved two versions of the vaccine: the Pfizer-BioNTech vaccine and the Moderna vaccine. They’re being distributed in tier groups based on greatest need.

Both require two doses for maximum effectiveness.

In the United Kingdom, a lack of vaccine doses has led health officials to announce that they will be delaying the vaccine booster shots and focusing on initial doses to reach a wider section of the population.

Normally, the booster COVID-19 vaccines would be given about 21 days after the initial vaccine. Now U.K. officials say booster shots can be delayed up to 12 weeks.

But experts warn this way of vaccinating the public hasn’t been fully tested.

The reason is due to supply. Officials are hoping that by delaying the booster shots, more people can get the initial dose and supply will catch up with demand in later weeks.

So, why is the United Kingdom’s decision considered a controversial move that’s receiving criticism from the FDA?

And what does this mean for immunity in the immediate future?

Recently, the FDA released a statement urging people who get the vaccine to stick to the authorized dosing schedules.

The two different mRNA vaccines that have been approved show an effectiveness of about 95 percent, but only after people have received both doses.

But surging COVID-19 cases have put pressure on U.S. and U.K. health officials to take action — whether that action is backed by science or not.

According to the U.K. Joint Committee on Vaccination and Immunization (JCVI): “Given the high level of protection afforded by the first dose, models suggest that initially vaccinating a greater number of people with a single dose will prevent more deaths and hospitalizations than vaccinating a smaller number of people with two doses.”

There are currently two versions of the vaccine being administered in the United Kingdom: the Pfizer-BioNTech vaccine and the AstraZeneca vaccine.

The AstraZeneca vaccine hasn’t been approved yet by the FDA in the United States.

JCVI reports that short-term vaccine effectiveness from the Pfizer-BioNTech vaccine is calculated at around 90 percent, though that’s not confirmed in the United States.

AstraZeneca’s first dose is showing 70 percent effectiveness.

The second dose, JCVI says, is still important for longer lasting protection.

It’s controversial for a few reasons.

First, administering only a single dose of the COVID-19 vaccine wasn’t the way the clinical trials were conducted, so it’s not clear what the expected outcomes will be if the boosters are delayed by many weeks.

The trials for both Pfizer-BioNTech and Moderna were conducted with two doses given within about 3 weeks, which has been proven to be highly effective.

There’s not enough data to know how effective a single dose and then delayed booster shot would be, but initially, the single dose would likely be considerably less effective.

“We don’t have the confirmed efficacy of one dose. That needs to be studied a bit more,” said Dr. Matthew Heinz, a hospitalist in Tucson, Arizona. “If you have one dose versus zero doses, one is better. But that is still suboptimal.”

“If many people are only getting one shot [of the vaccine], they will not have that 95 percent protection. We don’t have a complete understanding of what a single shot does when currently a booster shot is recommended,” Heinz added.

For many health experts, the goal of vaccination is to reach “herd immunity.”

To achieve herd immunity, 80 to 85 percent of the population has to be vaccinated to stop the virus from spreading widely.

Other concerns are that those who are only receiving one dose can still contract the virus, display symptoms, and transmit the virus, further increasing cases.

However, Heinz noted, with a single dose administered, an infection may not be a 10- or 14-day ordeal.

People with a single dose would likely not get the full brunt of COVID-19.

“A good analogy is our flu shot,” he said. “They are rarely perfect. Scientists and public health officials take a stab at what is going to be most common for the upcoming winter. Therefore, the efficacy is 15, 20, and 30 percent, but you still do get some protection. You may still get a flu, but it won’t be as severe or last as long.”

Other experts, however, see the United Kingdom’s decision as simply another alternative.

“There are many roads to Rome,” said Dr. William Schaffner, a Vanderbilt University professor of preventive medicine in the Department of Health Policy, as well as professor of medicine in the Division of Infectious Diseases. “These are two different strategies, and each has its advantages and disadvantages.”

“The first dose does indeed provide some partial protection,” he said. “That’s not the way it was authorized to be used, but it is a public health strategy. The advantage is that you give some degree of protection to the maximum number of people.”

The disadvantage, however, is that many of those people who receive their first dose will think that they’re completely immune and will begin to relax other safety measures, like mask wearing and physical distancing.

They may then expose themselves to risk.

“That is unfortunate,” Schaffner said. “The other thing is that the vaccine hasn’t been studied at longer intervals between doses. But with every other vaccine we’ve dealt with, longer intervals don’t matter very much.”

“We shouldn’t make too much of it,” he noted. “It’s a matter of reasonable people making reasonable decisions, and there is no single right decision.”

With the controversy brewing, it’s logical to ask: What’s the holdup? Why can’t we just make more of the vaccine and solve this problem?

The answer is simply scarcity of resources.

According to The New York Times, the reasons for the slow rollout are unclear, only that the task of distributing thousands of vaccine doses is a big undertaking — especially with so many health departments already spread too thin due to the effects of the pandemic.

“We want to do this as fast as possible, but also as safely as possible,” Heinz said.

“We, of course, want to do what we can to make the limited supply work for more people, and last longer for our health departments. But we don’t want to sacrifice too much in the way of effectiveness. There has to be a balance,” he said.

Heinz noted that the overarching theme right now is that we’re in a time of scarcity, but there will be a time when there’s widespread availability for the public.