Those were already well underway.

mRNA-induced production of protein in animal tissues was demonstrated in vivo in 1989. Yes, I know that's very different from large-scale manufacture of a reliable product. But still.

It just wasn't profitable to put a lot of research into. Vaccines are the most obvious application, and vaccines just aren't profitable most of the time. There are few endemic diseases in wealthy countries, and even fewer where you can sell every person a dose in a few years. For most diseases, the total number of doses sold during the patent period would be relatively small. For example, a potential hepatitis C vaccine would probably look like the hep B vaccine's deployment -- with some ~200 million hep B vaccines given the USA over the last 40 years. Compare to a similar number of COVID-19 vaccines sold in under 12 months.

The underlying technology may well be the cure for many types of cancer and a broad solution to most infectious disease. But again, that likely wouldn't pay off while the patents are in effect. So no point in investing heavily.

Pfizer and Moderna were both sitting on quite a lot of proprietary knowledge, based on the sheer volume of patents filed since early last year. Some basic research, hoping for some breakthrough, but mostly just waiting for an opportune time to develop it into something that would be profitable.

Based on the short time period that mRNA is active, couldn't they propose treatments where you need to be injected with more of it every month?

They'd gain a benefit over pills in that a nurse is required to inject the patient

IIRC yes but they were relegated to academic study. Something being successful on the market is a huge catalyst for other pharma companies to invest on the tech.

The vaccine community was already well aware of the potential of mRNA vaccines, it just needed a bit more development to mature. The pandemic provided that final push, but without the pandemic that would still have happened, just at a lower pace. They'd still be available and successful on the market in 2025 or so.

Protease inhibitors have more of a track record in humans than mRNA, having been used widely as a treatment for HIV. Maybe we're more comfortable with our understanding of any possible long term side effects?

Yeah apparently BioNTech is working on a mRna vaccine for cancer