• There's been a higher-than-expected number of heart inflammation cases in Covid vaccine recipients ages 16 to 24, according to the CDC.
• However, "at this point, the risk benefit still favors vaccination certainly in this age group," Dr. Scott Gottlieb told CNBC.
• The former FDA chief said there are many unanswered questions about the relationship between the vaccines and cases of myocarditis and pericarditis.

Rare instances of heart inflammation in young people after receiving their second Covid vaccine dose require further inquiry, Dr. Scott Gottlieb told CNBC on Friday.

However, the former Food and Drug Administration commissioner said the cases have mostly been mild and should not dissuade people from signing up for the two-shot regimens from Pfizer and Moderna.

"At this point, the risk/benefit still favors vaccination certainly in this age group," Gottlieb, a Pfizer board member, said in an interview on "Squawk Box." "That's what CDC and FDA have also affirmed."

A day earlier, the Centers for Disease Control and Prevention indicated it has seen a higher-than-projected number of cases of heart inflammation in 16-to-24-year-olds following their second Covid shot—  275 recorded occurrences compared with expectations of 10 to 102.

In people age 30 and below, there's been 475 total reports of myocarditis or pericarditis, which according to the CDC involves inflammation of the heart muscle or the lining around it. Men make up the vast majority of reported instances of post-vaccine myocarditis or pericarditis.

Of the 270 people who developed the conditions and have been discharged from the hospital, 81% have fully recovered, according to CDC data. The remaining 19% either still have symptoms or their status is not known. Fifteen people are still hospitalized, the CDC said.

Symptoms, which include chest pain and shortness of breath, typically develop when a few days of receiving the vaccine, according to the CDC.

Gottlieb said many questions remain about the connection between the heart inflammation and the Covid vaccines from Pfizer and Moderna.

"I think at this point you need to assume there's a causal relationship between the vaccine and these observations until you can prove otherwise," said Gottlieb, who led the FDA from 2017 to 2019 in the Trump administration.

Gottlieb said what's not known yet is whether there's something specific about the vaccines that are causing heart inflammation. "We know the vaccine induces inflammatory response. That's why you get a fever. That's why you get injection-site pain because your immune system is stimulated."

"Is this a more generalized inflammatory response from the vaccine that's localizing in the heart in some patients?" Gottlieb asked. "Or is this something that's more direct, where the vaccine itself is triggering some kind of very targeted immune reaction and it's manifesting in this way? We don't have the answers to these questions."

It's possible additional cases haven't been recorded, Gottlieb said, but "we are probably capturing most of the severe cases." He added, "When you look at the number of people who are having severe cases of pericarditis, it's very small numbers right now."

Roughly 141.5 million people in the U.S. have been fully vaccinated against Covid, according to CDC data. The vaccines have been critical in driving down the number of coronavirus cases in the U.S. to their lowest levels since early in the pandemic.