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New US coronavirus travel restrictions are likely to have an outsized impact on Mexico, which is also struggling with an uncontrolled outbreak of the virus and record-breaking deaths.
Among Joe Biden’s flurry of executive orders on Thursday was a new set of rules requiring all travellers entering the US by sea, air or land to show proof of a recent negative coronavirus test and self-quarantine or self-isolate after entry. The executive action also instructs federal officials to work with the governments of Mexico and Canada to draw up a coordinated plan for border crossings.
The chair of the Winton Centre for Risk and Evidence Communication at Cambridge, David Spiegelhalter, and Anthony Masters, a statistical ambassador for the Royal Statistical Society, explain the meaning of a Covid vaccine having “90% efficacy”.
Imagine 100 people are ill with Covid-19.“90% efficacy” means if only they’d had the vaccine, on average only 10 would have got ill. Vaccine efficacy is the relative reduction in the risk: whatever your risk was before, it is reduced by 90% if you get vaccinated. There is a lot of confusion about this number: it does not mean there is a 10% chance of getting Covid-19 if vaccinated – that chance will be massively lower than 10%.