CDC advises some people wait longer between COVID-19 vaccine doses over heart inflammation risk

The Centers for Disease Control and Prevention (CDC) on Wednesday said younger males should consider waiting longer between doses of the Pfizer-BioNTech and Moderna COVID-19 vaccines in order to reduce the risk of a rare form of heart inflammation.

In an update on its website, the agency suggested an eight-week interval between the first and second doses of a primary mRNA vaccine schedule. 

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The “mRNA COVID-19 vaccines are safe and effective at the FDA-approved or FDA-authorized intervals, but a longer interval may be considered for some populations. While absolute risk remains small, the relative risk for myocarditis is higher for males ages 12-39 years, and this risk might be reduced by extending the interval between the first and second dose,” the agency said. 

The CDC cited studies in adolescents and adults showing the small risk of myocarditis associated with vaccines might be reduced and peak antibody responses and vaccine effectiveness may be increased with an interval longer than four weeks. 

“Extending the interval beyond 8 weeks has not been shown to provide additional benefit. There are currently no data available for children ages 11 years and younger. Therefore, an 8-week interval may be optimal for some people ages 12 years and older, especially for males ages 12–39 years,” the CDC said.

Notably, the change will not impact many people, as the CDC reports 73% of people age 12 and older already have gotten two doses of vaccine.

In addition, while the suggestion to wait up to two months doesn’t apply, the initial, shorter interval is still recommended for those with weakened immune systems, people age 65 and older and anyone who needs fast protection due to risk of severe disease.

The government authorized the Pfizer shots as a two-dose series spaced three weeks apart, and the Moderna shots to be spaced four weeks apart.

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Mostly adolescent and young adult males developed myocarditis after the second shot and the CDC says that – among males ages 18 to 39 – the condition has been reported in about 68 per 1 million getting the second Moderna dose and about 47 per 1 million getting the second Pfizer dose.

The CDC and the Advisory Committee on Immunization Practices (ACIP) have recommended and the Food and Drug Administration (FDA) has authorized Pfizer vaccines in children ages 5-11 and adolescents ages 12-17 based on the determination that benefits of COVID-19 vaccination outweigh the risk of serious side effects. 

“After reviewing available data on the risks and benefits, ACIP and CDC determined that the benefits (e.g., prevention of COVID-19 cases and its severe outcomes) outweigh the risks of myocarditis and pericarditis after receipt of mRNA COVID-19 vaccines for children, adolescents and young adults.,” it said.

The CDC also highlighted that most myocarditis and pericarditis patients have been hospitalized for short periods and that most have achieved resolution of acute symptoms. 

Symptoms of myocarditis or pericarditis include chest pain, shortness of breath or tachycardia, and people should seek care if such symptoms develop, particularly in the week after vaccination.

The CDC said accumulating evidence suggests a higher risk for myocarditis following Moderna vaccination compared with Pfizer vaccination, with data showing the risk for myocarditis or pericarditis lower in young adults after mRNA booster doses.

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A booster dose of a COVID-19 vaccine is recommended for everyone ages 12 years and older. 

A three-dose primary mRNA COVID-19 vaccine series is recommended for people ages 5 years and older who are moderately or severely immunocompromised.

The Associated Press contributed to this report.