Insights from the CDC's Covid-19 vaccine meeting.

The CDC's Advisory Committee on Immune Practices held a public meeting yesterday. Here are some highlights.

Earlier this week, the FDA made changes to the US Covid-19 vaccine strategy. Today, the CDC’s Advisory Committee on Immunization Practices (ACIP) held a public meeting in which they ratified the FDA approach.

Many of my thoughts on this new approach can be found in Tuesday’s Inside Medicine, as well as some quotations I gave to the New York Times and an interview I did on the PBS News Hour yesterday.

For those interested in some next-level Inside Medicine, here are some ad hoc comments and observations I have after watching the ACIP presentations today.

mRNA Covid-19 bivalent booster vaccines are safe.

The bivalent vaccines are safe. There had been a momentary concern about the possibility of an uptick in a certain type of stroke in some older patients. But there turned out to be no statistical difference between bivalent vaccine recipients compared to similar people who did not get boosted. This was not news. We already got this information from a New England Journal of Medicine report earlier this month, which showed no increases in strokes, heart attacks, or dangerous blood clots in the lungs. While I’m glad we have a system that operates on a hair-trigger to look into any potential safety issues, the downside is that nothing-burgers make headlines prematurely. When initial concerns turn out to be unfounded, the headlines are less viral. But that’s just the cost of doing science responsibly.

Covid-19 Vaccine and booster uptake.

Original slide source: CDC/ACIP.

Looking at Covid-19 vaccination uptake, I see three weak spots (other than the fact that the number of fully vaccinated people just ought to be 100%, but I’ll stop dreaming), which I’ve outlined in red above.

First, the vaccination rate in children under 2 years is atrociously low. While it would be nice to see higher rates in older children and young adults, the risk to children under age 2 (and really, under 1) is astronomically higher than all other kids, and even many adults. (Infants are hospitalized at uncomfortably high rates). The vulnerable time is infancy. We need to get these rates up. (More on pediatric vaccines later in the column.)

Second, the 50-64-year age group vaccine rates are a problem. The risk of severe or fatal Covid-19 in this group is lower than for people ages ≥65, but not so much lower that the vaccine rates and booster rates should be as low as they are.

Third, the bivalent booster is incrementally better than the monovalent vaccine it replaced, but a 43% uptake in seniors just doesn’t cut it. For seniors (and severely immunocompromised people), staying up-to date on vaccinations is crucial.

So why did I skip over the really low rates in kids and young adults? Because in all honesty, it’s more important to get booster rates up in seniors. For example, it would be epidemiologically preferable to get senior boosting rates to increase just 3% than it would be to get rates in younger people to go up 30% or more.

The bivalent vaccines and primary series in kids and adults.

The bivalent vaccine will now be given as the primary series, as we learned earlier this week. We also saw a bunch of slides on vaccine effectiveness in children. No surprise, the value that the Covid-19 vaccines have in preventing symptomatic infection is moderate and wanes quickly. (We didn’t get new data on vaccine performance against severe disease, although in the past, epidemiology studies and antibody level data implied protection against these bad outcomes .)

All told, the US is going to keep the original timing for the primary series in place for children, meaning two (Moderna) or three (Pfizer-BioNTech) doses. Meanwhile, for adults not yet vaccinated, a one-dose primary series of the bivalent vaccine will now suffice.

The data supporting the one-dose primary series for adults are lacking so far. The idea makes sense, but is that enough? I’m not sure. The CDC’s rationale here is that a vast majority of US adults have already been infected with the coronavirus at least once. Counting infection as dose #1, means that a single dose of vaccine would, in effect, be acting like dose #2.

Again, a nice idea, but I’d need to see more data to be convinced.

My friend and colleague, the great Dr. John Moore of Cornell Medical College, was shall-we-say, less restrained on this point, telling the New York Times that the “F.D.A. has consistently over-interpreted the performance of the bivalent formulation when given as a booster….Now it seems to have gone beyond the science and decided it has some kind of magic power as a first dose.”

One thing that does make sense to me, though, is maintaining the two or three dose primary series for children. Even though most kids as young as under 4 have been infected, the group that clearly has much lower rates of infection is infants. Infants become eligible for Covid-19 vaccines at 6 months of age. Depending on community Covid levels during their early lives, very few of them are likely to have been infected prior to vaccination. So, keeping the two or three dose series in place for children makes sense to me.

Covid-19 vaccines treat two diseases.

In this last section, I want to talk through an idea I’ve spoken about with colleagues for a long time, which is that the “novel” coronavirus should, I believe, actually be thought of as two distinct diseases. Understanding this helps explain why our vaccines work so well (and for so long) in some respects, while waning so quickly in others.