“An 8-week interval may be optimal for some people ages 12 years and older, especially for males ages 12 to 39 years,” the agency says.
The longer interval would reduce the risk of myocarditis, a type of inflammation in the heart muscles, the CDC says. Though cases of vaccine-related myocarditis are rare, more have occurred in this age group of males than other groups.
“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 CDC says.
Previously, the CDC recommended that people get their second vaccine dose 3 weeks after the first Pfizer dose and 4 weeks after the first Moderna dose. That recommendation remains for people who are 65 or older, have compromised immune systems, or need rapid protection because of concerns about severe disease or high community transmission.
Children 11 and younger should still get the second Pfizer dose 3 weeks after the first, the CDC says.
The CDC didn’t change the guidance on how long to wait for a booster dose. It’s still 5 months after a second dose of Pfizer or Moderna or 2 months after the single-dose Johnson & Johnson vaccine.
CNN reported that the CDC’s Advisory Committee on Immunization Practices recommended this month that guidance be updated on the time between doses of the Moderna and Pfizer vaccines. The benefits of the vaccines still outweigh the risk of myocarditis, a CDC doctor said.
Canada extended the time between first and second doses to 16 weeks when vaccine shots were in short supply, then changed the interval to 8 weeks when the shots became more available, CNN reported.
"Eight weeks can create the opportunity to develop stronger and more broad immunity, which could be important in future waves of the pandemic," Matthew Tunis, PhD, executive secretary for the Canadian National Advisory Committee on Immunization, told CNN.