Herd immunity unlikely: The world may need to live with the virus

The world may need to learn to live with the virus.

Early in the pandemic, there was hope that the world would one day achieve herd immunity, the point when the coronavirus lacks enough hosts to spread easily. But over a year later, the virus is crushing India with a fearsome second wave and surging in countries from Asia to Latin America.

Experts now say it is changing too quickly, new more contagious variants are spreading too easily and vaccinations are happening too slowly for herd immunity to be within reach anytime soon.

That means if the virus continues to run rampant through much of the world, it is well on its way to becoming endemic, an ever-present threat.

Virus variants are tearing through places where people gather in large numbers with few or no pandemic protocols, like wearing masks and distancing, according to Dr. David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine.

While the outbreak in India is capturing the most attention, Dr. Heymann said the pervasive reach of the virus means that the likelihood is growing that it will persist in most parts of the world.

As more people contract the virus, developing some level of immunity, and the pace of vaccinations accelerates, future outbreaks won’t be on the scale of those devastating India and Brazil, Dr. Heymann said. Smaller outbreaks that are less deadly but a constant threat should be expected, Dr. Heymann said.

“This is the natural progression of many infections we have in humans, whether it is tuberculosis or H.I.V.,” said Dr. Heymann, a former member of the Epidemiology Intelligence Service at the Centers for Disease Control and Prevention and a former senior official at the World Health Organization. “They have become endemic and we have learned to live with them and we learn how to do risk assessments and how to protect those we want to protect.” ...

Only two countries have fully vaccinated more than half of their populations, according to the Our World in Data project at the University of Oxford. They are Israel and the East African nation of the Seychelles, an archipelago with a population of fewer than 100,000. And just a handful of other countries have at least partially vaccinated nearly 50 percent or more, including Britain, tiny Bhutan, and the United States. ...