We do recognize that an extended interval between doses may not be an option for everyone, particularly high-risk groups like the elderly, those with multiple comorbid conditions, or those with moderate to severe immunocompromised conditions. Therefore, a growing consensus for an extended interval of 8 weeks represents a "sweet spot" to both reduce this risk and address the concerns of unvaccinated adults and/or their children. Nationally, only 28% of children 5 to 11 years old had received at least one dose of COVID-19 vaccine as of mid-January. Although the quantified risk of myocarditis/pericarditis is much higher with actual infection from COVID-19 than from mRNA vaccines, fear of this rare side effect has stopped some adults from getting vaccinated and prevented many parents from vaccinating their children. A pre-print study of 19.7 million doses of Pfizer and Moderna vaccine given to participants in Canada demonstrated a significantly lower risk of myocarditis/pericarditis in those who were vaccinated on an extended 8-week dosing schedule. Notably, the risk of these side effects is highest after the second dose.
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The rates are extremely low (67.5 and 46.8 cases per million, respectively for Moderna and Pfizer) and the vast majority of cases are self-limiting with full recovery. In the context of unanimously approving Moderna's vaccine, ACIP members discussed the rate of myocarditis/pericarditis in those who received both Pfizer and Moderna vaccines. B cells triggered by the vaccines are able to produce new antibodies if they ever see the virus, even if it has mutated. Another study of healthcare workers verified the increased antibody response from extending the interval from 3-4 weeks to 6-8 weeks with Pfizer, and also showed a 7-fold increase in the magnitude of the B-cell response. COVID-specific T cells protect us against variants, including omicron.
T cells amplify the body's response to a virus, help recruit cells to attack the pathogen, and generally protect us from severe disease. One important immunologic study verified that extending the interval of the Pfizer vaccine from 3 to 6 weeks not only increased antibody levels, but also, enriched T cells against COVID-19. Beyond the many studies showing a higher antibody response, several have shown that increasing the interval between doses amplifies the cellular immune response, which is important for durability. Many immunologic studies have shown higher SARS-CoV-2 antibody levels from extending the time between doses.
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