When the new crown epidemic raged around the world last year, governments around the world were vigorously promoting the hope of “herd immunity”, that is, when enough people are immune, the virus will no longer be able to spread. Now, this seems to be just a fantasy. The thinking at the time was that after a large proportion of the population (perhaps 60%-70%) were vaccinated or had antibodies developed due to infection, the epidemic would naturally slow down and basically subside.
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However, the emergence of new mutants such as Delta that are more powerful and may cause breakthrough infections has raised the threshold of herd immunity to a height that is almost impossible to achieve.
The rapid spread of delta is increasing the number of infections in the United States, Britain and other countries. These countries have experienced severe epidemics before, and may have achieved a certain degree of natural immunity, and the vaccination rate has exceeded 50%. In Australia and other places where the previous anti-epidemic results have been outstanding and the cases have almost been cleared, Delta also gave them a head-on.
The American Academy of Infectious Diseases estimated this month that Delta has pushed the threshold for herd immunity to more than 80%, possibly closer to 90%. At the same time, the unwillingness of some people to vaccinate and the availability of vaccines mean that most countries cannot even get close to the initial threshold.
“Can we achieve herd immunity? No, by definition, we can’t,” said Greg Poland of Mayo Clinic’s Vaccine Research Group.
He bluntly said that even if the vaccination rate reaches 95%, it will not be achieved. “The continuous emergence of more infectious variants and the vaccination rate will always be a difficult race.”
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