The prior recommended interval between initial doses was three weeks for the Pfizer-BioNTech vaccine and four weeks for the Moderna vaccine. This timeline is still recommended by the CDC for individuals who are immunocompromised, over 65 years old or in need of rapid protection against the coronavirus.
According to the CDC, however, leaving more time between the first two doses of mRNA COVID-19 vaccines may reduce the risk for severe side effects such as myocarditis, or inflammation of the heart wall.