Insufficient evidence exists to support any strategy where patients either delay their second dose or only receive one dose of COVID-19 mRNA vaccines, even if they have been previously infected with the virus, CDC staff told the agency’s Advisory Committee on Immunization Practices (ACIP) at its Monday meeting.
And ACIP committee members seemed to agree, with few showing any enthusiasm for alternate mRNA vaccine dosing intervals, including delaying a second dose beyond current recommendations. They cited the imprecise estimates about effectiveness of a single dose, and also the potential that one dose won’t be protective against emerging variants. Moreover, the products’ emergency use authorization (EUA) came with the condition that they be given as two doses on a specific schedule.
Previously, NIAID Director Anthony Fauci, MD, weighed in with his hesitancy about one-dose mRNA vaccine studies, and ACIP members were similarly skeptical.
“We don’t have sufficient data to delay second doses beyond what’s currently recommended,” said Grace Lee, MD, ACIP member, of Stanford University in California.
CDC recommendations currently allow up to 6 weeks between doses, though only if it is not possible to adhere to the recommended interval of either 21 days for the Pfizer/BioNTech vaccine or 28 days for Moderna’s.
Agency staff indicated similar lack of data about one dose in people previously infected with COVID-19, saying large-scale antibody testing is not feasible, and that with the correlate of protection currently unknown, they would be unable to extrapolate antibody studies to vaccine effectiveness. This approach, too, runs contrary to the EUA.
Committee members seemed more split on this subject. Helen Keipp Talbot, MD, of Vanderbilt University in Nashville, said more data about prior COVID patients was unnecessary, because “we’ve all taken immunology.” She argued the initial infection acted as the first “dose” of virus — the “prime” — and the vaccine would act as the second “dose” — the “boost.”
However, ACIP Chair José Romero, MD, wasn’t convinced, saying that works only if vaccinated individuals have adequate or high antibody titers.
“What happens to individuals that have no antibodies or low antibodies? Are we certain they have enough memory B-cells to boost to levels that will be protective?” said Romero, who is the director of the Arkansas Department of Health.
Another wrinkle in this debate was the variants. CDC researchers presented data bolstering the point that postponing a second dose of COVID-19 vaccine may leave some less protected against variants, including data showing minimal to no neutralization of B.1.351 (the so-called South African variant) after one dose, but improved neutralization of both B.1.351 and B.1.1.7 (the so-called U.K. variant) after the second dose.
Another topic explored was more “age brackets” for eligibility for those under age 65 (such as age 60-64 or 55-59). Panel members appeared unreceptive, saying it would exacerbate existing disparities in access.
“In our rush to administer vaccines, we cannot sacrifice equity. I clearly want to state I am not in favor of any type of age eligibility bracket under age 65 because of the inequity that will cause,” Romero said.
Most committee members also expressed distaste for the idea of prioritizing people with “two or more high-risk medical conditions,” not only citing equity concerns, but also privacy, because it would force people to reveal protected health information to get the vaccine. They also wanted the CDC’s list of “high-risk” conditions clarified.
“Don’t try to make it whose disease is more severe than others,” Talbot said. “I don’t need to know which one, I don’t need to know how many, I just need to know you have one.”
Lee also pointed out requiring two or more high-risk medical condition would make it harder for pregnant women to get the vaccine, as pregnancy is the only high-risk condition for most of them.
Members also said this could lead to more of a punitive approach versus an improvement.
“Whether or not I get high risk condition A versus high risk condition B correct isn’t as important as providing access,” Lee said. “We need to continue to improve on getting it right versus penalizing folks that may not be perfect.”