Parents who are gung ho to get their young children vaccinated are groaning about this on social media, having been told before to expect emergency authorization for infants and toddlers within weeks. Now they’re being told to expect it within months, maybe around April or May.

Considering how small the risk of serious illness is to young children, it’s hard to grok why any parent would refrain from letting their kids do certain activities until they’re vaccinated. Maybe it’s more about transmission, fearing that an unvaccinated child is more likely to get infected and to spread the virus to a vulnerable grandparent, putting their life at risk potentially.

Vaccination does reduce the chances that an infected person will infect someone else but it doesn’t eliminate it, especially with Omicron. If you’re that worried about your elderly parent catching Omicron from your child, why would you risk letting them be in the same indoor space together even after the kid has been vaccinated?

Anyway, Pfizer is pulling its application — for now — because its two-dose regimen in trials didn’t produce sufficient antibodies in kids aged two to four. It did produce enough antibodies in younger children, aged six to 23 months. Initially, in the interest of speeding up the process, the FDA had invited Pfizer to submit all of its data on the two-dose regimen for possible authorization and then to submit further data later on how effective a three-dose regimen was by comparison. The plan, it seems, was to speed things up by letting kids get the first two shots while the experts figured out whether a third was useful or not.

The NYT called that “highly unusual” but doing it that way would have mimicked how the vaccines rolled out for adults. The two-dose regimen was authorized in December 2020 and the booster was authorized almost a year later. But instead of sticking to that scheme, the FDA suddenly decided in a “striking reversal” that it wants to wait until the three-dose data is in before it begins considering the application. So Pfizer postponed its application for approval.

What gives? Why did the FDA suddenly change its mind?

Pfizer announced late last year that in a clinical trial of children aged 2 to 4 years old, two doses of vaccine failed to generate antibody levels on par with those seen in people aged 16 to 25 after two shots. Paradoxically, two doses given to infants aged 6 months to 23 months did generate antibody levels similar to those seen in the 16- to 25-year-olds, levels that are deemed to equate with protection…

It was not immediately clear exactly what led to the decision to cancel the meeting. Some sources, who spoke on condition of anonymity, said data from Pfizer to the FDA had come in late, and FDA staffers may have needed more time to vet them. It’s also possible new issues emerged with those data. The FDA normally posts extensive briefing documents prepared by both vaccine manufacturers and by FDA staff two working days before a scheduled meeting, although it does not have to meet this deadline. As of Friday morning, none was published.

“Two people familiar with the FDA’s plans said there had already been a lot of pushback on the agency from outside experts who had concerns that Pfizer’s data wasn’t sufficient,” NBC reported. Is that it, that the data wasn’t “sufficient”? Or did it have more to do with the fact that the two-dose results for kids aged two to four were underwhelming? Vaccine experts whispered to the WSJ that the weak two-dose results for those children left the agency in a bind. If they approved the two-dose regimen anyway in the hope/expectation that a third dose would eventually be shown to provide strong protection, what would they do if the third dose later turned out to be a bust as well?

How would they justify having authorized a two-dose vaccination course that ended up not being very effective?

Not a good look for an agency that’s already dealing with a high degree of vaccine skepticism from the population. Remember, the feds were so anxious about public opinion of the vaccines that they ended up suspending Johnson & Johnson’s vaccine temporarily last year when the data showed a very small risk of blood clotting to certain recipients. That was their way of trying to show Americans that they were being transparent about any health concerns related to the shots. (Although it ended up backfiring by seemingly discouraging some people who were ambivalent about vaccination from getting jabbed.) They may be doing the same thing by slow-walking Pfizer’s vaccine for young kids. If it would hurt the legitimacy of the FDA — and the vaccines — for the agency to approve a two-dose course that doesn’t work very well then they shouldn’t approve it. They should wait for the three-dose data to see if that works better.

Stat is also hearing from sources that the FDA was concerned about what the public would have thought of its strategy of approving two lackluster doses initially and then waiting on data about a third dose. Quote: “Some outside experts have characterized this strategy as aggressive and unusual, and have worried it could backfire by making some parents less inclined to vaccinate their kids.”

Sounds like all Pfizer needs to do is bump up the dosage for the cohort aged two to four, though. If the vaccine produces sufficient antibodies in younger kids and older kids, there must be a dosage that’s optimal for that group in the middle too. But approving the two-dose regimen when the proper dosage isn’t known yet would also create a major perception problem, potentially. “They want to give my kid a shot when they’re not even sure how much vaccine should be in it?!” Parents would be spooked. Anti-vaxxers would have a field day.

Is it worth running that risk in order to speed up vaccination of an age group that’s at almost no risk of dying from COVID?

Emily Oster was waiting on the two-dose data, which the FDA was supposed to publish today, and is mystified by their sudden about-face. Go read her post, in which she tries to reassure highly risk-averse parents that the vaccine being postponed doesn’t mean their three-year-olds should be quarantined until April. They’ll be fine. Note the comments too, in which one parent says she’s “livid” at the postponement — not because she’s afraid of her child getting sick but because local quarantine rules in her blue community are draconian for the unvaccinated. If her young kid tests positive, she’ll be stuck at home for days and someone will have to stay home to look after her. All because the local rules won’t bend to accommodate children who can’t be vaccinated yet.

Exit question: If the two-dose data for kids aged six to 23 months looks good, why can’t the FDA move forward with approval for them?