World may never reach herd immunity against COVID – Experts

The thinking was that the pandemic would ebb and then mostly fade once a chunk of the population, possibly 60% to 70%, was vaccinated or had resistance through a previous infection. But new variants like delta, which are more transmissible and have been shown to evade these protections in some cases, are moving the bar for herd immunity near impossibly high levels.

Delta is spurring widening outbreaks in countries like the U.S. and U.K. that have already been walloped by the virus, and presumably have some measure of natural immunity in addition to vaccination rates of more than 50%. It’s also hitting nations that have until now managed to keep the virus out almost entirely, like Australia and China.

This month, the Infectious Diseases Society of America estimated that delta had pushed the threshold for herd immunity to well over 80% and possibly close to 90%. Public health officials like Anthony Fauci have drawn controversy by shifting the goalposts over the past year, increasing the number of people who need protection before hitting herd immunity. Meanwhile, vaccine hesitancy and supply issues mean most countries won’t get close to even the original numbers.

“Will we get herd immunity? No, very unlikely, by definition,” said Greg Poland, director of the Vaccine Research Group at the Mayo Clinic in Rochester, Minnesota.

Even a vaccination rate of as high as 95% wouldn’t achieve it, he said. “It is a neck and neck race between the development of ever more highly transmissible variants which develop the capacity to evade immunity, and immunization rates.”

Nature isn’t going to solve the problem, either. It’s unclear how long natural immunity gained from surviving COVID-19 will last, and whether it will be effective at fighting off new strains. Future variants, including some that could evade immunity even more efficiently than delta, raise questions about how — and when — this will be over.

“If it was as simple as getting the infection once means you are immune for life, that would be great, but I don’t think that’s the case,” said S.V. Mahadevan, director of South Asia Outreach at the Center for Asian Health Research and Education at Stanford University Medical Center. “That’s a troubling problem.”

Already there are signs that some people, and some places — like Brazil and other countries in South America — are being battered a second time by newer strains.

Without herd immunity, the virus could linger for decades in some form, possibly forcing the world’s most powerful nations to adjust their diverging strategies on opening borders and economies.

Vaccines so far haven’t been the quick fix some had hoped for. Israel, among the most vaccinated countries in the world, has already started administering booster shots, amid evidence that the current immunizations aren’t offering the protection that was hoped. Last week, the U.S. said Americans with weakened immune systems will get a third dose.

The most powerful vaccines, including the mRNA shots from Pfizer Inc., BioNTech SE and Moderna Inc., would make it easier to reach high levels of immunity since they are so effective. Yet breakthrough infections — cases in the immunized — are possible with even these shots. Other vaccines, including those made by China’s developers, AstraZeneca Plc and Johnson & Johnson, may offer even less protection.

Herd immunity is a real thing, protecting much of the world against viral threats from the measles to polio. Scientists credit it for helping eradicate smallpox. Having herd immunity as a goal likely helped the world embrace measures like wearing masks and social distancing. But it also created a false narrative.

Despite evidence that it will be difficult or impossible to reach herd immunity, many public health officials aren’t willing to give up on it. Governments worldwide are focused on widening inoculation programmes.

Yet the individualistic approach of many countries, and vaccine shortages, are contributing to the global problem. The risk of the virus remains for everyone, as long as any nation is experiencing massive outbreaks.

The world is unlikely to put the pandemic behind it until 2022 at the earliest, experts say. And that target could be pushed back if the virus mounts another metamorphosis to become even more transmissible or even better at evading resistance.

The Spanish flu of 1918 shows how COVID may play out, the Mayo Clinic’s Poland said. It’s likely that variants will continue to emerge, forcing the use of boosters or routine immunizations, targeted to the newer strains. – BLOOMBERG