U.S. health officials say that some people getting the Pfizer or Moderna COVID-19 vaccines should consider waiting up to 8 weeks before getting their second dose of the vaccine, lengthening the time between doses from a previous 3-4 weeks.

The Centers for Disease Control and Prevention quietly changed its advice on spacing for the shots on Tuesday. CDC officials say the move was in response to research showing that the longer time between the first and second doses of the shot, the less enduring protection the vaccine can provide.

Research suggests that 12-64 year olds, especially males aged 12-29, can benefit more from the longer spacing.

The CDC added that the longer spacing can also help diminish an already rare side effect: a form of heart inflammation seen in some young men.

But it is important to note that the CDC says this change doesn't apply to everyone, as 73% of people age 12+ have already received 2 doses of the vaccine. The shorter intervals between shots is still recommended for those with weakened immune systems and those who are 65+.