Dr. Scott Gottlieb told CNBC the U.S. will still have to experience “the hardest stretch” of the coronavirus pandemic without the benefits of a vaccine, despite the positive news earlier Monday from Pfizer.Gottlieb, a former U.S. Food and Drug Administration commissioner in the Trump administration, is a member of Pfizer’s board of directors.”The vaccine is really a 2021 event in terms of when it’s going to provide protective immunity to that initial tranche” of recipients, Gottlieb said on “Squawk Box,” shortly after the Pfizer announcement. “Then in terms of when it would be widely available, I think the hope still is … you could have a vaccine broadly maybe the end of the second quarter, maybe into the third quarter. You’re looking at having the vaccine available in time for the fall 2021 Covid season.”U.S. pharmaceutical giant Pfizer announced that the vaccine it’s developing with German firm BioNTech is more than 90% effective in preventing Covid-19 for those who had no evidence of previously being infected.”I think we need to remember that we have perhaps a brief, but very hard stretch, ahead of us,” Gottlieb said as the U.S. has set a series of all-time highs for new daily Covid-19 cases in recent days. He told CNBC on Friday he believes the cases may “explode in several weeks.”However, Gottlieb said Monday, “We ought to take this positive news and recognize there may be a much better future ahead of us. … We may be available to have a vaccine broadly available at some point in 2021 and do everything we can to continue to protect people who are vulnerable to this virus over this period of time, recognizing it may be a brief of time.”Pfizer and BioNTech expect to have up to 50 million doses of their vaccine produced this year and up to 1.3 billion doses in 2021. It requires to doses per person.Gottlieb said the initial group of recipients, should it be granted emergency use authorization by the FDA, are likely to be “a selection portion of the elderly population because they’re at most risk from Covid.”There are about 50.5 million confirmed cases of the coronavirus globally and more than 1.2 million people have died, according to data compiled by Johns Hopkins University. Nearly 10 million of those infections and over 237,500 fatalities have been in the U.S.Since the coronavirus emerged late last year in China, it has spread rapidly across the world. Drugmakers have accelerated their vaccine developments in hopes of ending the pandemic, which upended daily life and brought about an accompanying economic crisis.”I think what this does is affirm that a vaccine does seem possible,” Gottlieb said. “This is a meaningful result, a very meaningful result, exceeds the expectations based on the interim analysis. And if the data does hold up on the final read out from the full clinical trial, I think it’s light at the end of the tunnel.”Disclosure: Scott Gottlieb is a CNBC contributor and is a member of the boards of Pfizer, genetic testing start-up Tempus and biotech company Illumina. Gottlieb also serves as co-chair of Norwegian Cruise Line Holdings′ and Royal Caribbean’s “Healthy Sail Panel.” Subscribe to CNBC PRO for exclusive insights and analysis, and live business day programming from around the world.