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Opinion | Without a vaccine, chasing herd immunity to stop coronavirus is doomed to fail
- To achieve herd immunity for Covid-19, at least 60 to 70 per cent of the global population would need to have had the infection, which, without a vaccine, may take years
- Until we have an effective vaccine, we have to outsmart this virus by understanding where and how it spreads and not giving it a chance to do so
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Why you can trust SCMP
As the global struggle to contain Covid-19 continues and pandemic fatigue sets in, some are advocating for a so-called natural herd immunity strategy, which they argue can be safely achieved through “focused protection”.
This concept entails fully reopening societies while shielding the elderly and people with comorbidity to achieve herd immunity in the absence of a vaccine within six months. It sounds simple, but the facts tell us otherwise.
First, herd immunity is achieved by protecting people from a virus with the use of a vaccine, not by exposing them to it. For example, herd immunity against measles requires about 95 per cent of people to be vaccinated.
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Once immunised against measles, they act as a protective buffer preventing the virus from circulating and infecting the remaining 5 per cent of the population who are unvaccinated.
Second, we are nowhere close to the levels of immunity required to stop this disease transmitting. We know from seroepidemiology studies that less than 10 per cent of the global population has shown evidence of infection. That means the vast majority of people are still susceptible to the Sars-CoV-2 virus.
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