NEW YORK (BLOOMBERG) - The spread of the Delta coronavirus variant has pushed the threshold for herd immunity to well over 80 per cent and potentially approaching 90 per cent, according to a briefing by the Infectious Diseases Society of America on Tuesday (Aug 3).

       That represents a "much higher" bar than previous estimates of 60 per cent to 70 per cent, because Delta is twice as transmissible, said Assistant Professor Richard Franco at the University of Alabama at Birmingham.

       "It is becoming clear that this is a very dangerous, way more dangerous virus than the original one," Prof Franco said.

       Herd immunity is based on the idea that when a certain percentage of the population has been vaccinated against the virus or gains immunity by a previous infection, it helps protect the broader population and reduce transmission.

       Nearly 60 per cent of Americans have received at least one dose of a coronavirus vaccine, and about 50 per cent have been fully vaccinated, representing about 165 million individuals, according to data from the Centres for Disease Control and Prevention.

       Some 35 million people in the United States, meanwhile, have tested positive for the virus over the course of the pandemic.

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