I am not a biology people. But this question has been bothering me for months.
I read the news that, even if an effective vaccine (for Covid-19) successfully created, the transport of the vaccine and its acceptance might still be a big problem; some vaccine need to be kept at extremely low temperature prior to using.
But then, what if the vaccine could cause one recipient to fall sick and the recipient spreads the mild disease to other people? This might sound bad, but then the community will develop immunity against the notorious Covid far much faster, more effectively and possibly free of charge for most of us. Instead of injecting the recipients one by one, just spread the vaccine like how Covid-19 spread.
Maybe the vaccine contains only part of the virus but not living virus, but considering those infected by mild cowpox will develop immunity against small pox, can't we just synthesize the cowpox-analogue for Covid-19? (Cowpox might not be spread through air, or from people to people, I am just saying, use highly contagious living virus that cause mild symptoms as vaccine)
Or is it because deliberately spreading viruses might be labelled as immoral so no one attempted this?