I have a Master's degree in biochemistry.
The reason why we might have a vaccine in only 9 months (the record for development to approval is 5 years) is that scientists predicted that coronaviruses would be one of the most likely viruses to cause a pandemic. We saw the potential with SARS. We saw the potential with MERS. The NIH and WHO funded research into coronaviruses, so the technology infrastructure was present. It only took a matter of weeks to characterize its genome and run tests to determine a vaccine's feasibility.
Search of: vaccine | Covid19 - List Results - ClinicalTrials.gov
271 trials. For the same disease. This includes vaccines, antibody therapies, small molecule repurposement, etc.
If you sink all your resources into ONE vaccine candidate and it fails, then you have nothing. What do you do? Go back and select the next candidate? That will take another year to be pushed through.
It's like the stock market. You can't sink ALL of your savings into one stock. If you do and an event you did not foresee comes, like a pandemic, you could lose ALL your money. Then you start from nothing. If you don't diversify, you will get crushed.
It was announced that a promising Eli Lilly/NIH antibody candidate bombed out of the clinic. It also turns out the Remdesivir,
THE drug being touted by doctors, relayed by the media, for improving outcomes for COVID patients actually doesn't work. This is why clinical trials are done in the first place.
Furthermore, some candidates may be better at provoking an immune response than others. Some people might not be able to receive certain candidates due to pre-existing conditions. Formulations may be different for children than for adults. Some candidates have a very short shelf life (hours). Some candidates require extreme storage conditions (in dry ice).
HIV is a different beast. The good thing is that you need sexual contact, blood transfusion, or skin puncture by a contaminated foreign object to transmit the disease. Unlike COVID, HIV doesn't have the number antigens (targets) that coronaviruses have. Furthermore, HIV mutates just as quickly, so any target is too unstable to be continually recognized by the immune system. So vaccines, with current technology, is highly unlikely. Complicating things is that HIV invades a certain type of T-cell that is responsible for coordinating the immune response. As the cells multiply to mount an immune response, the virus multiplies. It's a feedback loop. When there are too many HIV particles in the blood, you get diagnosed with AIDS and your time on Earth is short.
Look, I don't defend the business end of the pharmaceutical industry, who do some very shady shit. Much more shady shit than you may be aware of. This is all at the behest of "shareholders" including yourself if you have a 401K. I do defend the scientists, academic and industrial, who are practically working themselves to death to make sure that you can go back to the gym and support your local restaurants. Our economy depends on it.