The CDC has recommended extending the interval between the first and second doses of the Pfizer (NYSE:PFE) and Moderna (NASDAQ:MRNA) COVID-19 vaccines up to eight weeks for some individuals.
The guidance for those vaccines was formerly 21 and 28 days, respectively.
CDC notes that an eight-week interval could be preferred for some individuals 12 and older — especially males aged 12 to 39. The extended window may reduce the risk of myocarditis.
A three-week interval for Pfizer-BioNTech and a four-week interval for Moderna is preferred for individuals who are moderately to severely immunocompromised and adults who are at least 65.
While myocarditis associated with mRNA vaccines remains rare, passive surveillance reporting in the U.S. confirms an increase in the condition — especially in adolescent males and young men, according to a report in JAMA.
Extending the interval between the first and second doses may result in superior vaccine effectiveness, although increasing the gap beyond eight weeks has no confirmed added benefits.
According to data from the UK, an eight-week gap appeared to generate a superior immune response than other intervals tested, according to a report from BBC.
There are also no data involving extending the time interval in children 11 and younger.