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Experts debate the effectiveness of a single dose versus a double dose of the COVID-19 vaccine

Johnson & Johnson's one-shot vaccine shows promise
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Posted at 11:18 AM, Jan 15, 2021
and last updated 2021-01-15 13:18:48-05

DENVER — The vaccine’s arrival in Colorado last month was rightly celebrated by the governor and others.

But the rollout here and in other states has been somewhat chaotic, messy and frustrating – especially for higher-risk Coloradans trying to get the vaccine.

“There seems to be quite a bit of confusion out there in terms of the availability and the timing,” said one 70-plus-year-old Coloradan.

As the state continues to iron out those issues, some experts, including Dr. Moncef Slaoui on the Operation Warp Speed team, have suggested we can achieve greater immunity by ‘spreading out’ the vaccine and only giving a single dose or half dose to younger, lower-risk individuals.

For example, instead of giving two doses 3-4 weeks apart, as recommended for the Pfizer and Moderna vaccines, some suggest waiting as many as 12 weeks to give the second dose to lower risk individuals, like those 18-55 years old. We took those ideas to experts here in Colorado.

“The ideas are very intriguing to potentially get more vaccine out to more people more quickly,” said Dr. James Neid, head of infection control at The Medical Center of Aurora.

"That is what has been proposed in the United Kingdom,” said Dr. Thomas Campbell, chief clinical research officer for UCHealth.

Let’s start there.

Yes, the U.K., for example, is now suggesting a second dose at the end of 12 weeks.

But Dr. Campbell points out that’s the AstraZeneca vaccine, which is different from what’s approved in the U.S.

“It might work, but we don’t know with Pfizer and Moderna whether it works,” Campbell said.

As he explains, two-dose and even three-dose vaccines are very common. The Hepatitis B vaccine, for example, is given three times – day zero, one month later and six months after the first dose.

“And that’s because the body’s immune system tends to respond much better the second time than the first time,” Campbell said. “And it develops higher antibody levels. Depending on the vaccine and depending on the infection – more than one dose is often necessary.”

There is a one-dose COVID-19 vaccine being developed right now by Johnson and Johnson.

“It’s expected that the data from their Phase 3 trial will become available later this month,” Campbell said.

“Well, clearly, that’s preferable,” Neid said. “But the downside is it’s taking much longer for that vaccine to be developed, whereas the mRNA technology is available quicker. It’s available now.”

Neid said it’s simply too early to know if spreading out the doses of the Pfizer and Moderna vaccines would reduce their effectiveness.

“I think we don’t know the answer to that,” Neid said. “If you try to extrapolate the data from the Pfizer study and the Moderna study, there is a suggestion that a single dose will have some lasting immunity that may be effective and even more effective than what’s been in the trial. However, we just don’t know.”

Neid says changing course too soon or too often could erode public trust in the vaccine and the system.

“Certainly there are going to be a lot of opinions,” he said. “There are already a lot of well-thought-through models to suggest that this is a potentially good idea – we just don’t know yet. That, to me, is the biggest risk of changing tact too quickly.”

Campbell agrees, especially given the limited data available about waiting for longer intervals between doses.

“Being that we’re in the middle of a raging pandemic, as you expand that time interval between the two, there’s more of a chance for someone to be exposed and get infected, while not having complete, high-level immunity,” Campbell said. “And patience is required while we gather data to make a more firm opinion as to whether that would work.”

So, the debate continues — which both Neid and Campbell believe is healthy.

“Nobody’s entrenched on one set pattern for the future,” Neid said.

“It could well be that the approach we’re using now will be modified,” Campbell said.

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