https://www.technologyreview.com/s/615375/what-is-herd-immunity-and-can-it-stop-the-coronavirus/

Even then, vaccine makers can find themselves in a losing race with nature to see which protects the herd first.

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The current germ’s rate of spread is higher than that of the ordinary flu, but similar to that of novel emergent influenzas that have occasionally swept the globe before. “That is similar to pandemic flu of 1918, and it implies that the end of this epidemic is going to require nearly 50% of the population to be immune, either from a vaccine, which is not on the immediate horizon, or from natural infection,” Harvard University epidemiologist Marc Lipsitch told a gathering of experts on a video call this weekend.

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Whether it’s 50% or 60% or 80%, those figures imply billions infected and millions killed around the world, although the more slowly the pandemic unfolds, the greater the chance for new treatments or vaccines to help.

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The newest epidemiological models developed in the UK now recommend aggressive “suppression” of the virus. The basic tactics being urged would be to isolate sick people, try to reduce social contacts by 75%, and close schools. Those economically costly measures could continue for many months.

“Suppressing transmission means that we won’t build up herd immunity,” says Azra Ghani, the lead epidemiologist on the new model of the outbreak from Imperial College London. The trade-off of success is “that we are driving it down to such a low level that we have to keep those [measures] in place.”