CDC Staff: After Third Dose for the Immunocompromised, Hold Off on ‘Booster’

Immunocompromised people who received an additional dose of COVID-19 vaccine are among those not yet indicated for boosters, and the jury is still out on boosters for previously infected individuals, CDC staff said on Tuesday.

During a call with clinicians, CDC staff clarified the definitions of “additional dose” and “booster dose,” noting that an additional dose is for moderately to severely immunocompromised people at least 28 days after the initial two-dose series, in whom the primary series is likely to provide insufficient protection. A booster dose is administered 6 months after the two-dose primary series, when an initial immune response to the vaccine is likely to have waned over time, they said.

During a Q&A session, clinicians asked if immunocompromised people need to receive a booster dose if they already received an additional dose, if they fall into a population in which it’s recommended.

“At this point, CDC has not issued a recommendation for a COVID-19 vaccine booster dose at least 6 months after a primary series” for these people, said Neela Goswami, MD, of the CDC. “The most important thing is that people received the primary series plus a third dose.”

She added that there would be future meetings about a booster dose in this population “down the line.”

She also verified that research indicates a primary vaccination series “decreases the risk of future infections” in people with prior COVID-19 infection, but “the efficacy of a booster dose for fully vaccinated people who have already had COVID-19 is not yet known.”

“We do not recommend [serological] blood tests for this decision,” she added.

“Given the rapidly changing clinical, public health, and scientific landscape amidst the COVID-19 pandemic, an individual level assessment considering potential benefits and risks of a COVID-19 booster dose is needed where the data are uncertain,” she said.

Adults ages 18-64 with occupational risk exposure were defined as those in jobs with “close proximity to other people” and “unavoidable, frequent interactions with unvaccinated people,” such as healthcare workers and teachers, she explained.

Potential adverse events with a booster dose include very rare risks of myocarditis and pericarditis, as well as an even rarer risk of anaphylaxis. They also include reactogenicity, though data published in an early edition of the Morbidity and Mortality Weekly Report found similar reactogenicity after the third dose as the second dose, with a similar pattern of adverse reactions.

Among 12,591 v-safe registrants who completed a health check-in from August 12 to September 19 for three doses of Pfizer vaccine, almost three-quarters reported systemic reactions after the third dose, while 77% reported systemic reactions after the second dose.

Among 15,503 participants who reported systemic reactions during the week after an additional vaccine dose, 56.0% reported fatigue and 43% reported headache.

Goswami reiterated that the definition of “fully vaccinated” will not change “for public health purposes,” and remains two doses of mRNA vaccine or one dose of the Johnson & Johnson vaccine at least 2 weeks after the second dose.

When clinicians asked if two doses of Johnson & Johnson’s vaccine will eventually be considered as “fully vaccinated” among those who received this vaccine, CDC staff said that data are “currently under review.”

Data on a Pfizer booster in those who received a different primary series are also under review.

For those individuals choosing to receive a booster dose, CDC staff noted that the COVID-19 vaccine can be administered on the same day as other vaccinations, including the flu shot.