@CarolineHumer Hi Caroline. That is the million dollar question. The short answer is that nobody is quite sure #AskReuters /1
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@CarolineHumer Current calls to vaccinate >70% of the population are important and right on. Even if we reach herd immunity well before that point, we still want to keep going to allow a safe buffer, and to prevent super spreader events which can happen despite surpassing herd immunity. /2
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@CarolineHumer That said, we may get to herd immunity after vaccinating a smaller % of the population. First, previously infected people contribute to herd immunity which is relevant in many states (NY, NJ, Dakotas & others...) #AskReuters /3
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@CarolineHumer Second, R0 is higher in certain sectors of the population than others which also generally means, fewer people might need to get vaccinated to get us to herd immunity #AskReuters /4
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@CarolineHumer On the other hand, the new variants will necessitate wider vaccination to achieve herd immunity. This is one of the reasons that these strains were not great news. #AskReuters /5
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@CarolineHumer A final tricky variable is that people may continue to socially distance / mask relative to 2019 so this may also mean less people need to be vaccinated to get us there. #AskReuters /6
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@CarolineHumer So this is why, no (good) epidemiologist is willing to provide a precise #. It is a moving target and may differ between countries / regions. That said, I think the magic number is likely well under 70%. We'll see! /7
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@joshua_schiffer @fredhutch @CarolineHumer Need about 70% vaccinated or 230 million plus 50-60 million previously infected gets you to about 90% which leaves little room for virus reproduction. 40 million vaccinations per month means 6-7 months, or July-August
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