In February, independent data scientist Youyang Gu changed the name of his
popular COVID-19 forecasting model from ‘Path to Herd Immunity’ to ‘Path to Normality’. He said that reaching a herd-immunity threshold was looking unlikely because of factors such as vaccine hesitancy, the emergence of new variants and the delayed arrival of vaccinations for children.
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It’s unclear whether vaccines prevent transmission
The key to herd immunity is that, even if a person becomes infected, there are too few susceptible hosts around to maintain transmission — those who have been vaccinated or have already had the infection cannot contract and spread the virus. The COVID-19 vaccines developed by Moderna and Pfizer–BioNTech, for example, are extremely effective at preventing symptomatic disease, but it is still unclear whether they protect people from becoming infected, or from spreading the virus to others. That poses a problem for herd immunity.
“Herd immunity is only relevant if we have a transmission-blocking vaccine. If we don’t, then the only way to get herd immunity in the population is to give everyone the vaccine,”