Decoded: Why Delta variant of Covid-19 is making herd immunity harder

The more the coronavirus circulates, the more opportunity it has to mutate in ways that enhance its ability to evade the immunity people have gained

Many countries are counting on vaccines to build sufficient immunity in their populations so that SARS-CoV-2, the virus that causes Covid-19, isn’t able to find enough people to infect, causing transmission to eventually stop. But even in countries with a high proportion of people inoculated with highly effective vaccines, it’s unclear if it’s possible to reach the so-called herd immunity threshold anytime soon.

Will vaccines eliminate Covid-19?

There’s considerable uncertainty about that. One scientific paper calculated that if a vaccine could provide a lifelong, fail-safe shield against infection with SARS-CoV-2, it would need to reach 60-72 per cent of people to establish