‘Mix and match’ boosters could pose logistical hurdles for states

A health care worker prepares a vaccine for administration at a vaccination clinic
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The Biden administration will allow people to get a coronavirus booster vaccine that’s different from their initial dose, a move that experts say will give doctors and states flexibility, and smooth over confusing messages over boosters.  

However, public health officials have expressed concern about more transient populations, like migrants and the homeless, who received the one-shot regimen of the Johnson & Johnson vaccine. These groups, experts say, may be harder to reach for a second dose.  

Other medical professionals hope that the federal government issues a more nuanced guidance on mixing booster shots, with a focus on receiving a dose of a person’s original series.  

Federal officials have been trying to balance the differing and sometimes contradictory messages surrounding the Biden administration’s booster campaign. While the administration initially told the public everyone over the age of 18 who wanted a booster could get one, the reality is more complicated. 

Pfizer was granted emergency use authorization for a booster dose of its vaccine six months after the prime dose for a limited population: people over the age of 65, as well as people who are 18 and older and are at risk of severe disease due to an underlying condition or risky working conditions.  

The Food and Drug Administration (FDA) granted Moderna the same exact authorization on Wednesday. The Johnson & Johnson booster will now be available to anyone 18 or older two months after their first dose. 

William Moss, an infectious disease expert at Johns Hopkins School of Public Health, said the differing eligibility is likely to make the booster campaign messaging complicated. Allowing different doses could compound the issue, he said. 

“But at the same time, I do think they kind of put themselves in this position where it would be very odd to recommend booster doses for those who got two doses of Pfizer, and not those who got two doses of Moderna,” he said.  

A highly anticipated preprint study on “mixing and matching” vaccines from the National Institutes of Health (NIH) found that administering booster doses with any of the three vaccines currently licensed or authorized for emergency use in the U.S. is safe and will generate an immune response.  

Experts said if people need a booster, they may be better off getting the same vaccine as their initial series. But in some places, like nursing homes, access to the original vaccine may not be possible.  

“States are going to have a pretty good supply of all three of the vaccines. So, it’s really just the logistics of having all three in different locations. Sometimes there’s been a problem that the pharmacy will only have Moderna, so people coming in to get Pfizer are unable to get a booster,” said Marcus Plescia, chief medical officer at the Association of State and Territorial Health Officials.  

Plescia said he hoped the administration would emphasize that people who need a booster should receive the same vaccine as the prime dose, if available. 

“I would say though that we need to be cautious about, in the general population, doing mix and match. We probably should try to stick to having people get the booster that’s the same as the primary series that they had, just because we don’t have a lot of science or study of, is mix and match fully effective and is the same,” Plescia said.  

Kirsten Lyke, a professor of medicine at the University of Maryland, presented the NIH study last week to an FDA vaccine advisory panel. Lyke emphasized that the data were preliminary but said the study appeared to show that boosting with a different vaccine from the primary shot provided a higher immune response.  

“What I would note is that the neutralizing antibodies did increase in response to any boost of the primary vaccination series,” Lyke told the panel. But she said the study was not designed to tell people which particular brand might be best to boost with. 

Still, the study indicated people who received a booster dose of either the Moderna or Pfizer vaccines had a higher increase in their antibody responses more often than those who received an extra dose of Johnson & Johnson’s vaccine. 

Johnson & Johnson’s vaccine has shown to be less effective than either of the mRNA vaccines made by Pfizer-BioNTech or Moderna. Therefore, public health officials have focused on the best way to ensure that 15 million people who received Johnson & Johnson’s vaccine are well-protected. 

But state officials are specifically concerned about the logistical hurdles in administering booster shots to many of the people who received the Johnson & Johnson vaccine. The single-dose shot made it easier to administer to homeless populations and migrant workers, but those same people will be difficult to reach for a second dose.  

“Now with the recognition that Johnson & Johnson is probably at its base two vaccines and should be given as such, that does start to open up the floodgates a little bit related to reidentifying some of the people that had transit social situations,” said Clay Marsh, West Virginia’s COVID-19 czar. 

Marsh said the state is prepared to send teams into homeless encampments, shelters and community kitchens to find “people that might be living a little bit off the grid.”  

“We very well might miss some of those people in this next round, but we continue to work on ways that we can provide access and messaging, so that you know we are able to connect to people,” Marsh said. 

But even though the J&J vaccine doesn’t measure up to the mRNA vaccines, it still provides good protection against severe disease and hospitalization.   

“It’s still much better than nothing. So even if we can’t find all these people, having one dose [is] certainly better than having no doses,” Marsh said.


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