ACIP Embraces Spikevax Amid Serious Talk of Changing mRNA Dosing Interval

The CDC’s Advisory Committee on Immunization Practices (ACIP) unanimously backed the fully approved Moderna COVID-19 vaccine (Spikevax), but engaged in serious discussion over the dosing interval for both Moderna and Pfizer’s mRNA vaccines.

In a speedy 13-0 vote, ACIP members said they favored a standard recommendation for the Moderna vaccine after reviewing its benefits and harms, a decision described as “straightforward” by ACIP chair Grace Lee, MD, MPH, of Stanford University School of Medicine in California. Shortly after the vote, CDC director Rochelle Walensky, MD, MPH, endorsed the recommendation, upgrading the interim recommendation for Moderna’s two-dose primary series to a full recommendation for people ages 18 and older.

It also came to light during the meeting that for people who are moderately or severely immunocompromised, the CDC anticipates that boosters will be recommended starting 3 months after the third dose of an mRNA vaccine. This is due to concern about their initial immune response and loss of protection over time, particularly during period of high community transmission, according to Elisha Hall, PhD, of the CDC.

Regarding the dosing intervals for average individuals, two doses of Moderna have been separated by 28 days in clinical practice for more than a year under FDA emergency use authorization. However, CDC staffers now say the accumulating international evidence (from Canada and the U.K., for example) supports an 8-week interval between COVID-19 vaccine doses going forward in the U.S.

CDC’s Sara Oliver, MD, MSPH, said the agency’s COVID-19 vaccine work group proposed this change on the basis of “limited but emerging” data suggesting extended intervals to be associated with higher antibody responses, better vaccine effectiveness against SARS-CoV-2 infection and hospitalization, and reduced myocarditis risk.

A potential downside of the 8-week interval is that an individual’s risk of getting COVID-19 likely increases the longer they are only partially vaccinated with a single dose, Oliver cautioned.

ACIP members voiced support for the extended interval between doses with the option of shorter intervals for certain groups that need early protection.

Under the current vaccine dosing schedule, myocarditis remains a rare but serious side effect that has disproportionately affected young men. Based on passive surveillance through Jan. 13, 2022, myocarditis reached a high of 40.0 cases per 1 million doses in men ages 18 to 24 years after their second dose of the Moderna vaccine.

Prognosis was fairly good for these individuals. In a pooling of Pfizer and Moderna mRNA vaccine recipients ages 12 to 29 who developed myocarditis, most reported no impact on their quality of life and not missing school or work at least 90 days after their myocarditis diagnosis. Ian Kracalik, PhD, MPH, of the CDC, reported that hospital readmissions were observed in 4% and there were no deaths.

Most of the patients who were judged by cardiologists to be recovered nevertheless had lingering symptoms or cardiac abnormalities. The most common abnormality on recent cardiac testing was late gadolinium enhancement on cardiac MRI.

Benefits of COVID-19 vaccination under the current schedule still far outweigh its risks, even in men under 40, Oliver maintained.

“I still have a sense of wonder on what’s been accomplished and a deep sense of gratitude. We have two COVID vaccines that are fully licensed and authorized while still following all the regulatory policies in place before the pandemic,” said ACIP member Matthew Daley, MD, of Kaiser Permanente Colorado, Aurora.

He cited an estimate that the vaccines have averted 1.1 million deaths in the U.S. alone and urged that the public not take them for granted.

The proposed 8-week dosing interval was not subject to a vote by ACIP and has not been implemented by regulators.