How many people invest in dollars, or euros, or yen? Not many, yet that doesn't seem to affect their values. Anyway, only the investors care about the price and investors aren't needed.
Holders of any currency care about the price, or purchasing power. I know multiple people living in the UK who avoid holding any of their savings in Pound sterling, because of its weakness over the past decade or two.
vaccine is already in trial phase as we speak. and there are quite number of institutions and pharma companies that are into developing the vaccine.
That might be true, but it's still going to be months until one hits the market even if a successful vaccine gets developed. And having a vaccine won't instantly eliminate all this fear and hysteria that's crippling markets--and I wish I could confidently estimate how long it's going to take for bitcoin, stocks, metals, and everything else to bounce back, but I don't have a clue.
Nobody has a clue.
The Chinese government has been testing a Japanese flu drug on COVID-19. They say it's clearly effective and safe. It's not a vaccine, but it offers some hope on the treatment side.