Younger males taking Pfizer and Moderna vaccines should consider waiting longer than four weeks between the first and second doses, this is according to the Centers for Disease Control and Prevention (CDC), which has changed its advice on spacing the shots to eight weeks.
CDC officials said they were reacting to research showing that the longer interval can provide more enduring protection against the coronavirus.
Research suggests that 12- to 64-year-olds, especially males ages 12 to 39, can benefit from the longer spacing, the CDC said.
The CDC recommends that other eligible individuals wait three weeks between Pfizer shots and four weeks between Moderna doses, particularly the elderly and those with compromised immune systems.
“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,” CDC stated.
Myocarditis is an inflammation of the heart muscle that can result in serious health problems. It most commonly occurs after viral infections, but the CDC has also found a link between Moderna and Pfizer shots and myocarditis, particularly after the second dose.
According to the CDC, previous studies in adolescents aged between 12 and 17, and adults, showed a small risk of myocarditis associated with mRNA Covid-19 vaccines that might be reduced, and peak antibody responses and vaccine effectiveness may be increased with an interval longer than four weeks.
“Extending the interval beyond eight weeks has not been shown to provide additional benefit,” the CDC noted.
The risk of myocarditis among men aged 18 to 39 is about 1.5 times higher after a second Moderna dose than with Pfizer’s vaccine.
Men in this age group report about 68 myocarditis cases per one million Moderna second doses administered, compared with 47 myocarditis cases per 1 million Pfizer second doses administered.
The CDC has also noted that most patients who develop myocarditis after Covid vaccination respond well to medicine and recover fully.
According to the Department of Health and Human Services, people face a much higher risk of developing myocarditis after Covid infection than vaccines.
Early in the pandemic, there was intense pressure to adopt as tight a vaccination schedule as possible because of how fast the virus was spreading.
In Kenya and other countries that had fewer vaccines at the onset of the pandemic, the World Health Organisation (WHO) recommended an interval of up to 12 weeks between the doses. This was meant to focus on achieving a high first dose coverage in the high priority groups.
However, the latest WHO interim recommendations for the Pfizer vaccine issued on January 21, 2022 and Moderna Vaccines issued on February 22, 2022 suggest an interval of eight weeks between doses because of the lower risk of myocarditis or pericarditis.
In Kenya, many of those who took Moderna got their second dose after 28 days.