It turns out it’s a little complicated. Pre-Covid, you can find evidence that profits were rather slim on vaccines. Seems Covid may have changed that for companie. Pre-Covid, the margins were rather slim, and historically, companies stopped making them because of that. Seems like pre-Covid, they made up about 2-3% of the pharma profits. Covid changed the equation, at least for Covid vaccines - and probably other mRNA vaccines, as well, most likely because it’s new tech and because of patents.

This was written in 2015:

https://www.theatlantic.com/business/archive/2015/02/vaccines-are-profitable-so-what/385214/

Not only do pediatricians and doctors often lose money on vaccine administration, it wasn’t too long ago that the vaccine industry was struggling with slim profit margins and shortages. The Economist wrote that “for decades vaccines were a neglected corner of the drugs business, with old technology, little investment and abysmal profit margins. Many firms sold their vaccine divisions to concentrate on more profitable drugs.”

In fact, vaccines were so unprofitable that some companies stopped making them altogether. In 1967, there were 26 vaccine manufactures. That number dropped to 17 by 1980. Ten years ago, the financial incentives to produce vaccines were so weak that there was growing concern that pharmaceutical companies were abandoning the vaccine business for selling more-profitable daily drug treatments. Compared with drugs that require daily doses, vaccines are only administered once a year or a lifetime. The pharmaceutical company Wyeth (which has since been acquired by Pfizer) reported that they stopped making the flu vaccine because the margins were so low.