The Pfizer CEO said people will “likely” need a third booster shot after 12 months of being fully vaccinated — and vaccine boosters may be a thing for years to come.

Since the start of the pandemic, some researchers have speculated that in years to come, the world may deal with COVID-19 by repeating shots every year or so. Researchers were stunningly quick to develop not one but several working vaccines, which is great news — but few vaccines last forever.

Many believe this is also the case with COVID-19. It’s unlikely that COVID-19 vaccines will offer lifetime protection as with measles, and more likely that persons will need regular shots, like the flu vaccine.

In the case of the flu vaccine, it has to be taken every year for two reasons: the first is that the body’s immune response can decrease over time, and the second is that the influenza virus is constantly adapting and changing, with new variants emerging. SARS-CoV-2 seems to be mutating much slower than the flu, but several concerning variants have already emerged — which is why it’s so important to generate immunity in as many people as possible.

“It is extremely important to suppress the pool of people that can be susceptible to the virus,” Pfizer CEO Albert Bourla told CNBC.

Existing vaccines seem to work well on the variants, with one exception: the South African variant. While data is scarce, it seems that all vaccines are relatively weak against the South African variant. In the current scenario, with billions of people worldwide likely to remain unvaccinated by the end of the year, we will likely need COVID-19 booster shots just like with the flu.

“A likely scenario is that there will be likely a need for a third dose, somewhere between six and 12 months and then from there, there will be an annual revaccination, but all of that needs to be confirmed. And again, the variants will play a key role,” he told CNBC’s Bertha Coombs during an event with CVS Health.

We’re still not sure just how long the vaccine will be effective for. Pfizer recently announced that the vaccine was still highly effective up to six months after the second dose, and as time passes, they will continue to monitor how long protection from the virus lasts. However, both Pfizer (with BioNTech) and Moderna are already in advanced trials for a third booster shot. Moderna expects the shot to be ready by autumn.

Earlier today, the CDC also announced that less than 1 in 10,000 vaccinated people seem to develop COVID-19. These cases, called “breakthrough cases” are exceedingly rare

“We see this with all vaccines in clinical trials,” NIAID director Anthony Fauci commented on the situation. “And in the real world, no vaccine is 100% efficacious or effective, which means that you will always see breakthrough infections regardless of the efficacy of your vaccine.”