Former director of the Centers for Disease Control and Prevention Dr. Tom Frieden told CNBC on Thursday that it might not be advisable to make what are known as Covid vaccination cards mandatory, as it could deter Americans from getting the shot.

“I think a vaccination certificate is something you should be entitled to, but you don’t have to,” said Frieden, who headed the health department under former President Barack Obama.

In an interview on Closing Bell, Frieden noted that some countries may require people to be vaccinated in order to travel and that some workplaces may implement vaccination mandates. For these reasons, it makes sense that people can easily prove that they received the vaccine, he said.

Indeed, a coalition called the Vaccination Credential Initiative announced Thursday that it would develop a digital Covid vaccination record. Microsoft, Salesforce and the Mayo Clinic, among others, are working on the development of technologies with which people can receive an encrypted digital version of vaccination protocols. It could then be stored in a digital wallet of your choice such as the Apple Wallet or Google Pay.

Vaccine hesitation, however, has been cited as a factor in the shaky rollout of Covid vaccination in the US, and peace fears that people who need to get a certificate to show they have been encountered could heighten fears.

“I would not be in favor of a system where people have to get something like this because you discourage people from vaccinating. It will be counterproductive,” he said.

Peace urged Americans in general to be patient with the slower than expected distribution of vaccines, and said public health precautions must be observed during the process.

“Nobody is going to change that,” he said. “We’ll still have to wear masks. We’ll still have to keep social distancing, and vaccination will be a month-long process in the United States.”