Come this fall, only older Americans and those with chronic health problems may be urged to get the Covid shot — assuming the vaccine is available at all.

For years now, scientific advisers to the Centers for Disease Control and Prevention have been debating whether to continue to recommend that Americans 6 months of age and older be immunized, or to switch to a so-called risk-based strategy targeting only the most vulnerable, as is the practice now in most other countries.

The advisers are expected to decide on a way forward at a meeting in June. But the debate may have become irrelevant. New requirements for clinical testing of vaccines, announced earlier this month, may delay the availability of shots that had formerly been updated annually without complicated trials.

“Substantial updates to existing vaccines — such as those related to seasonal strain changes or antigenic drift — may qualify as ‘new products’ and therefore require additional clinical evaluation,” the Department of Health and Human Services said in a statement.

That category includes the Covid shots and “may” even include the seasonal flu vaccine, according to Andrew Nixon, a spokesman for H.H.S.

The Food and Drug Administration has already asked Novavax for more clinical data before approving its Covid vaccine. (Currently it has emergency use authorization, not full approval, for people aged 12 and older.)