Advisory Committee on Immunization Practices Meeting on COVID-19 Vaccine Boosting: Day Two

The ACIP is back for Day Two of the COVID-19 vaccine boosters meeting. Today the focus will be on Moderna, Janssen, and heterologous boosting. They all got the green light from the FDA. I’ll be writing this post in real time according to the meeting schedule. Effectiveness and safety data will dominate the day. The afternoon presentations will cover the evidence, clinical implications, and policy questions. There will be a vote around 3:30 PM, CDT.

Questions were raised about the intention of using the same volume package of Moderna to administer both the primary series or the booster—just withdrawing half of the volume for the booster (50 micrograms in the booster as contrasted with 100 micrograms of the primary series). It sounds like there were concerns about making procedural mistakes in administration. Pharmacists would be concerned about this, and advocated for a separate booster dose package.

The Janssen vaccine booster data show that it’s safe, and increases protection against symptomatic COVID-19 infection. The combination of both humoral and cell-mediated immune responses associated with the Janssen vaccine primary single dose was emphasized. The booster dose is the same as the initial dose. The benefit of the Janssen booster dose might be higher when given at 6 months or later.

The NIH mix and match study showed relatively less boosting from the Janssen vaccine booster. The safety data were mostly reassuring. The study was non-randomized, correlates of protection are not completely elucidated, and not designed to compare between boosts. Heterologous boosts elicited similar or higher serologic responses as compared to their respective homologous booster responses. The 100-microgram dose of Moderna was used as the booster dose initially instead of the 50-microgram dose.

Update after the break:

The NIH mix and match study showed relatively less boosting from the Janssen vaccine booster. The safety data were mostly reassuring. The study was non-randomized, correlates of protection are not completely elucidated, and not designed to compare between boosts. Heterologous boosts elicited similar or higher serologic responses as compared to their respective homologous booster responses. The 100-microgram dose of Moderna was used as the booster dose initially instead of the 50-microgram dose.

Safety data were reviewed. Myocarditis/pericarditis rates (Dr. Nicky Klein’s slides) were highest in males age 18-39 years of age who got mRNA COVID-19 vaccines, generally after the second dose (data suggest maybe more from Moderna). Most patients recover. Thrombosis with thrombocytopenia syndrome (TTS) is still being monitored in the Janssen vaccine; it’s more common in women. There may be a causal association with TTS; it’s more common in females and it’s rare. There’s a lack of safety problems identified with current surveillance systems associated with heterologous dosing of mRNA and Janssen vaccines. Rare cases of Guillain-Barre Syndrome (GBS) occur with the Janssen vaccine. Risks of the aforementioned vaccines might be less with the booster doses. A couple of committee members expressed concerns about administration of a 2nd dose of Janssen as a booster given the rare but serious TTS and GBS adverse events. They favored heterologous boosting with mRNA vaccines instead.

After the break: Data were presented showing waning effectiveness of Moderna and Janssen vaccines. Vaccine effectiveness is lower in the Delta period. There is lower vaccine effectiveness for Janssen in those over age 65. In patients with chronic conditions, vaccine effectiveness in Moderna is better than in Janssen.  Moderna has 89-100% protection against severe disease. See the Summary and Conclusions slide of Dr. J. Jones (“COVID-19 vaccine effectiveness, primary series”). Someone asked about the role of risk behavior which could influence the estimate of vaccine effectiveness, which didn’t generate any solid answers.

See slide 5 in “Evidence for Recommendations” slide deck by Dooling for policy questions. Also see Summary slide 16 and slide 41, “Work Group Interpretation.”

The Clinical Considerations slide deck should be reviewed in its entirety. Although homologous boosting was initially recommended, the final language in the voting questions allowed for flexibility for heterologous boosting according to patient preference and product availability as well as taking into account the risk of TTS and GBS in those patients in higher risk groups for those adverse events. There was a consistent preference among some members for more permissive heterologous boosting.

There was a lot of discussion about the voting questions:

Vote #1: A single booster dose is recommended 6 months after completion of an mRNA series, in the same risk groups for whom CDC recommended a booster dose of Pfizer, under FDA EUA. This passed unanimously.

Vote #2: A single booster dose is recommended for persons aged 18 years, 2 months after receipt of the initial Janssen dose, under the FDA EUA. This passed unanimously.

The meeting was adjourned at around 4:20 PM, CDT.

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