I disagree with Gates’ assessment. According to many estimates, US may have anywhere from 60 to 100 million already exposed and 1-3 million new exposures per day. Assuming the vaccine also prevents people from carrying the virus in high doses as well as lowering the effects…

Say 60 million exposed and 1 million exposures per day, at the low end of estimates. That gets us to 150 million exposures per day by March at the current rate, or 40% of all Americans. Assuming they’re more or less evenly distributed and we vaccinate 100 million people by then, 40% of the remaining 230 million will likely have functional immunity, at least for the short-term, or 92 million.

192 million is coming up on 60%, which is only a few tens of millions away from the theoretical herd immunity threshold where spread isn’t exponential. Lock down areas with high infection rates for a few weeks in April, vaccinate some more, and this should burn out very quickly.

Maybe even earlier, if increased basic hygiene measures like masks, disinfection, and hand-washing lowered the herd-immunity threshold from its baseline early last year, when no one was doing much of anything.