75% seemed to be from immune people (from that nature article that showcased the maths). It's curious to me a 50%(correct me if I'm wrong) efficiency vaccine would work at 75%. I guess they had some natural immunity already?

EDIT: Nevermind, it would work anyway because the vaccines prevent more dangerous effects. So if you vaccinate at-risk people, ofc your deaths would lower

75% of population getting a vaccine with 50% efficacy could induce heard immunity, it depends what the reproduction rate is. Covid has a fairly high reproduction rate so it seems unlikely (although the 50% number might be incorrect), but as a general principle its possible for 75% of pop with 50% efficacy to trigger heard immunity if the viruses reproduction rate was low enough.

Mixed with other efforts, E.G. masking and social distancing, create sufficient reduction to make previously stalling campaigns sufficiently effective. Maybe enough to strangle the disease out if those other measures are held long enough.

From what I recall you'd need about 50% immunity for herd immunity to be reached at a minimum. Assuming 50% 3fficiency (worst case), you would need at least 13% already immune, which seems possible. But imo the efficiency might just be higher like parent said, or it might not be there yet, but deaths slow down because of the vaccine.

https://www.nature.com/articles/s41577-020-00451-5

> It's curious to me a 50%(correct me if I'm wrong) efficiency vaccine

From the article that's the lowest estimate:

> The results of the experiment could give a boost to the CoronaVac, which is being used by dozens of developing countries. There was some controversy about the vaccine this year, after clinical trials in Brazil, Indonesia and Turkey put its efficacy in a range of 50% to 90%.