Is "herd immunity" still a thing and roughly how many vaccines do we need before it starts lowering the number of deaths and infections? Anybody got any idea?
Yes it is but you need something like 60-90% of the population to be vaccinated for that. Which is a long way off.
The Vaccines will protect those who've had it, but it takes a month to go from the first jab to full protection and because it can't be dished out instantly it'll take months to get those at risk covered. For the next three or five months the only way to drop the death rate is to keep infections low, so tier 4 and lockdowns.