the total silence from anti viral drugs for Covid-19
That virus was first discovered only a few months ago. These things take time, and I disagree when you say it`s total silence. Johnson & Johnson for instance already announced this week they were going to start clinical studies this autumn.
Also, there has never been a successful vaccine against viruses of the coronavirus family. So the only work that can be used as a starting point is what was done during the original SARS epidemic.
Developing a vaccine takes time. You have to isolate the virus itself, also typically you have to isolate the antibodies that are generated by it, so you can study them. You have to figure out a way to generate something that is inactive, yet close enough to the original virus as to trigger the generation of antibodies.
Once you've got all of this, you need to produce this inactive agent, and start testing, which requires weeks, if not months of testing and data gathering.
And after all of this, IF you have a working product, you need to start mass manufacturing, then distributing, which can also take months.
In the J&J case for instance, they say their initial test to select one of multiple likely candidates took 12 weeks (they started working on it back in January).
I regularly see news about initial developments in this area. It just takes time. Going through the whole process is expected to take at best 8-12 months, more realistic estimates talk about 12-18 months.