Why Can’t We Give Half-Doses of the COVID Vaccine?

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After previously predicting that 20 million Americans would be given a COVID-19 vaccine by the end of 2020, the federal government was forced to admit resounding defeat, having administered only 2.1 million shots thus far. Stories about the slow rollout abound as people wait their turn — sometimes literally, camping out for vaccines that run out within a few hours. Meanwhile, the crisis has only worsened, and a new, more contagious variant of the virus is spreading rapidly. Given these factors, some scientists have argued that the COVID-19 vaccines (Pfizer’s and Moderna’s alike) should be split into “half-doses” or that the second dose, intended to be given three to four weeks after the first dose, should be delayed so more of the nation’s current supply can be quickly administered to more people.

The Cut spoke to Paul Offit, a pediatrician at Children’s Hospital of Philadelphia who specializes in infectious diseases and vaccines, about whether these plans might work.

Are half-doses and delayed second doses alternatives worth considering for the COVID-19 vaccines?

The short answer, according to Offit: No. “I don’t think either is an option,” he says. The purpose of the studies for both the Pfizer and Moderna vaccines, says Offit, was to determine the optimal dose. With that optimal dose and using a two-dose schedule, each vaccine has approximately 95 percent efficacy against the disease.

Neither study demonstrates whether a half-dose given twice or a single dose alone would be effective, says Offit. In presenting their vaccines to the FDA, he says, both companies stated that they lacked sufficient data to determine whether the vaccine would work as a single dose.

“I think the emphasis should be on mass-producing this vaccine, distributing it, and administering it, not trying to figure out a way to do something which is untested,” he adds.

What about the scientists who say, “Look, this isn’t ideal, but things are so bad we need to get the shots into as many arms as possible”?

In Offit’s opinion, the unknowns are too great. “You don’t know to what extent you’re protecting people [with half-doses] or for how long you’re protecting them,” he says.

In the studies done so far, he says, there have been a handful of cases in which people got the vaccine at the recommended dose but still got sick. This provides scientists with important information as to what level of neutralizing antibodies is needed to confer immunity. But in giving less of the vaccine, Offit worries that more people who get the vaccine would still get sick. “What you’ve done then is shaken what is already a fragile vaccine confidence in this country,” says Offit. “I saw someone on CNN say, ‘You don’t want perfect to be the enemy of the good,’ and I’m all for that. The problem here is that you don’t want the unknown to be the enemy of the known.”

Why does the vaccine need to be given in two doses?

Mainly because this is what we know, from research, works. “The first dose doesn’t induce nearly the level of antibody response as the second dose does,” says Offit. In the companies’ Phase I studies, in which scientists attempt to determine what dosage is necessary, both concluded that a single dose did not induce a strong antibody response. “It was only with that second dose that they had an antibody response that compared favorably to the antibody responses that were seen in people who had survived the infection,” adds Offit. The purpose of the nine months of research put into these vaccines, says Offit, was to determine the correct way to administer them. “To try one dose or half-doses is to make it up,” he says.

If we continue with the current plan of dosing and scheduling, what else should we be doing to speed up vaccination?

Here Offit reiterates that much of what we know about COVID-19 is unchanged: It’s a virus spread by small droplets. This is also true of the new, more contagious variant. It’s still essential to wear a mask and practice strict social distancing. On the individual level, these remain our best tools until the vaccine is widely available.

According to Offit, the first hard part of the pandemic response was developing a vaccine. The second hard part, he says, is actual vaccination. Developing the infrastructure to allow for faster vaccination should be the government’s first priority. “We should’ve put that infrastructure, or at least the money that can put that infrastructure, in place way earlier than we did,” says Offit. “You need to mass-produce this vaccine, distribute it, and you need to make sure it gets administered using a public-health system that currently is not designed for that.”

How will the Biden administration’s approach differ?

In short: We don’t really know yet. While Offit is optimistic that vaccination efforts will continue to ramp up, he has yet to see the clearly outlined plan he hopes for. “When President-elect Biden says we’re going to have 100 million people vaccinated in 100 days, that’s great: How?” says Offit. “You get tired of all the finger-pointing: Trump blames the states, Biden blames Trump — just come up with a plan, for God’s sake. That’s why you’re in that position.”

What’s a likely timeline for when vaccines might be largely available to the public?

Offit acknowledges that this pandemic has proved difficult to make predictions about: In March, he said he didn’t think there would be as many deaths from COVID-19 as there were from the flu in 2019, or approximately 60,000. “I was really wrong,” says Offit. “And I was wrong on international TV, because if you’re going to be wrong, don’t just tell your friends; say it in front of tens of millions of people.”

Still, he thinks it’s possible the vaccine will be widely available in early summer. “We’re at about 500,000 doses a day, so we’re getting better,” he says. “Our hospital is great at this: 12 people get vaccinated every 30 minutes. It’s doable.”

So What’s All This About Half-Doses of the COVID Vaccine?