For rich people (meaning the ~3 billion people that have some sort of access to medical infrastructure), it is a solved problem, but there are quite many people without any access to it. Even for those "solved problem" people, taking a pill every day to be protected is inconvenient. They might not take it every day, etc.
Also, even if it were a solved problem, the methodologies developed here can probably help with other viruses too in the future. This has already happened with the antivirals originally developed for HIV.
Also, even if it were a solved problem, the methodologies developed here can probably help with other viruses too in the future. This has already happened with the antivirals originally developed for HIV.