It is possible that two shots of Moderna's recently approved COVID vaccine will be adequate for long-term protection against the virus, according to the company's chief executive officer Stephane Bancel.

It is not a far-fetched notion, as a result of the resilience of the antibodies that the vaccine generates, Bancel said Friday.

"The antibody decay produced by the vaccine goes down very slowly...we believe there'll be protection for a couple of years," Bancel said according to a report by Reuters.

Moderna, which made headlines last year by producing a COVID vaccine in just a matter of weeks, was granted emergency use approval by the Food and Drug Administration for the treatment this week.

There are lingering questions about how the vaccine can provide a safe and effective level of immunity and how long it will last in older patients, whose immune systems deteriorate as they age, CBS News reported.

However, Bancel said more convincing data was still required to make a definitive evaluation. The immediate focus now is on the vaccine's safety and effectiveness on seniors, he said.

Bancel said the biotech company was about to prove that its COVID vaccine would also be effective against different strains of the disease detected in South Africa and Europe.

"The nightmare scenario...with a vaccine only working a month or two is, I think, out of the window," Bancel said during an event organized by financial services company Oddo BHF.

Moderna's shares were down 1% Thursday against the nearly 1.5% gain of the S&P 500 index.