The interval between first and second doses of the Pfizer and Moderna Covid-19 vaccines may be as long as eight weeks for certain people, the US Centers for Disease Control and Prevention said in vaccine guidance updated on Tuesday
Previous guidance said the second doses should be administered three weeks after the first shot of the Pfizer vaccine or four weeks after the first shot of the Moderna vaccine. The vaccines remain safe and effective at their original intervals, the CDC said, but extending the interval may reduce the risk of myocarditis, a type of heart inflammation, in some populations.
Booster doses continue to be recommended for most people five months after the two-dose primary series of an mRNA vaccine, or two months after a Johnson & Johnson single-dose primary vaccination. At a meeting of CDC's independent Advisory Committee on Immunization Practices earlier this month, agency officials suggested guidance could be updated to recommend lengthening the interval between first and second doses of the mRNA vaccines.CDC's Dr. Sara Oliver, an epidemic intelligence service officer with the division of viral diseases, told the committee that rates of myocarditis were lower with extended intervals between first and second doses.