Exactly! They tried to patent it, but it didn’t meet the requirements (https://www.ipeg.com/jonas-salk-inventor-of-the-polio-vaccine-could-you-patent-the-sun).

Notice how they tried to patent it “to prevent companies from making unlicensed, low-quality versions of the vaccine. There is no sign that the foundation intended to profit from a patent on the polio vaccine.”

EDIT: and on the other hand, you get things like insulin, where the patent was sold for $1 (https://www.vox.com/2019/4/3/18293950/why-is-insulin-so-expensive)