It is not only the hoteliers who dream of a bright and reborn summer. We are all. Escaping from the routine is in our nature, and if the boredom has lasted a year and a half our instinct to escape becomes imperious, voracious, zoo. The reality is stubborn, however, and seems determined to cloud our prospects. This is no longer the charming optimism of economists, who have been making technically correct calculations all year long, but resting on a shaky foundation, to save the summer campaign. The point is that scientists are beginning to doubt that the magic threshold of 70% of the immunized population, adding those vaccinated and those naturally infected, is a realistic goal. Herd immunity is not guaranteed either with vaccination running at full throttle, not before or after summer
Most regulators drive 60-70% as herd threshold, but there are several concurrent forces pushing it to the hike, as Christie Aschwanden reports for 'Nature' . First, it remains unclear whether the vaccines in use serve to slow the spread of the coronavirus. There is overwhelming evidence that they prevent severe COVID and death, even in nursing homes, but not that they stop the contagion. This does not reduce the importance of the vaccine, since it prevents deaths, but it greatly affects the estimation of the herd threshold, as seems common sense. That this issue has been resolved before the summer is a matter of faith.
It remains unclear whether the vaccines in use serve to slow the spread of the coronavirus
Then there is the bread pandemic, why it is named: it is a virus that has spread across the globe, and therefore does not support local solutions. Take the example of Israel, the world leader in vaccination against covid, which is in fact already touching the magic threshold of 60-70%. That's admirable, but Israel is surrounded by countries – Palestine, Egypt, Syria, Jordan and Lebanon – that have not vaccinated even 1% of their population. The Israeli prodigy will not be so so if he gets a stubborn trickle of new shoots from his neighbors. It's just one example, but it reveals another force struggling to raise the herd threshold. Herds are very large in our time, and they rarely respect borders
More problems. As there are no vaccines for children so far, the herd threshold for adults is not actually 70%, but rather close to 100%, to compensate for unvaccinated children. Then there is the question of mutants. Some variants of the virus spread more than the standard virus, or are reduced in recognition by antibodies, and this raises the herd threshold again. And another question that we tend to forget: the 70% threshold assumes measures of social restriction. If the measurements relax, you have to raise it. We cannot take the threshold of herd immunity as a religion. It is an estimate that depends on what happens from now on.
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