“Any variant that comes out, we take it and we test it against our vaccines,” says Bourla, who spoke today as part of a Fortune virtual event tied to the annual Davos meeting of the World Economic Forum.

When it comes to the variant of the coronavirus first detected in South Africa, studies indicate that the Pfizer vaccine produces fewer antibodies against this version of the virus. Bourla, however, said the company does “not believe that affects the performance of the vaccine against those variants.”

But, he added, it is likely that there will at some point be a variant that escapes the protection of the Pfizer vaccine. He says the company’s surveillance network would allow Pfizer to rapidly identify variants and then create a booster vaccine to fight them. He equated these boosters with having the operating system on your smartphone updated.

Bourla said he expects we will soon start to see some “real results” from the vaccination efforts and pointed to Israel as an example of a country that is making progress. The challenge right now is delivering the vaccine to as many people as possible, which he says is hamstrung by the need to coordinate different governments and national plans. But overall, he said, “I’m optimistic about our ability to control this pandemic.”

Larry Merlo, the CEO of CVS Health, also addressed the group, saying, “there’s optimism that by the time we get to the spring timeframe, there is now ample supply” of the vaccine. He said by June and July, hopefully, “we’re reaching that point of a large number of Americans vaccinated where we can begin to talk about herd immunity.”

Bourla said that one of the lessons of the pandemic is “the power of science, particularly in the hands of the private sector.” He said if someone had told him at the beginning of the pandemic that the company would develop a vaccine within nine months that’s 95% effective, he would not have believed it. He stressed the importance of maintaining a “vibrant science-based, innovation-based industry.”