How do researchers know what vaccines to make for the flu?

This year's flu season is "clearly one of the worst on record," Dr. Anthony Fauci said on the latest episode of "The Takeout" podcast.

The flu is currently widespread in every state but Hawaii and Oregon, and on Friday the CDC said at least 63 children have died from the flu so far this season, up from 53 reported last week.

"You never know until the end of the season how bad it is," Fauci told podcast host and CBS News Chief White House correspondent Major Garrett. "But there's no doubt, if you put 'flu' in different buckets, this is in the really serious bucket."

Fauci has served as Director of NIH's National Institute of Allergy and Infectious Diseases for more than three decades, and has advised five presidents on domestic and global health issues, including the HIV/AIDS epidemic in the 1980s and 1990s.  

Over breakfast at Bethesda, Maryland's, iconic eatery, Tastee Diner, Fauci explained how flu vaccination development works.

"The fact is, you take what we hope is an intelligent guess and projection because flu, unlike most any other viruses has an extraordinary capability of what we call drifting – namely, it mutates a little bit and it's a little bit different this year than next year, than the year before," he explained.

"So what you do is somewhere around March of a certain year – beginning of March – you make a projection of what you're going to get the following winter. And then you start making the vaccine and again, unfortunately, the vaccine takes several months – six months to make."

Fauci said that means he and his team then, therefore, "hope" the virus has not changed substantially from the vaccine that was decided to be made in the first place.

"It's difficult work and there are a lot of uncertainties to that," he said. "We generally do pretty well in predicting, but every once in a while the virus outsmarts us."

Fauci said he is "cautiously optimistic" that in a matter of years, not decades, that researchers, scientists and the broader medical community will get better at flu coverage.

"The perfect universal flu vaccine may be unattainable – and that's one vaccine against any possible influenza...but I do believe that within a few years, we'll be able to get a vaccine that would cover most of those drifts among, for example, H3N2 or H1N1," Fauci said, referring to the swine flu variant.

Fauci recommended Americans go get a flu shot if they haven't already and wash their hands frequently.

For more of Major's conversation with Fauci, including why children are particularly susceptible to the flu, download "The Takeout" podcast on Apple Podcasts, Google Play, Stitcher, or Spotify. New episodes are available every Friday morning.

Also, you can watch "The Takeout" on CBSN Friday and Saturday nights at 9pm ET/PT. For a full archive of "The Takeout" episodes, visit www.takeoutpodcast.com. And you can listen to "The Takeout" on select CBS News Radio affiliates (check your local listings).

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Producers: Arden Farhi, Katiana Krawchenko