Health and Healthcare Systems

WHO: Herd immunity is a long way off stopping COVID-19

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Few people wear masks as they walk on the beach pier in Oceanside, California. Image: REUTERS/Mike Blake

Anna Medaris Miller
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COVID-19

  • The WHO's Dr. Mike Ryan said "we're nowhere close" to having herd immunity levels needed to stop the coronavirus.
  • Only about 10% of the global population has antibodies against the infection, and experts don't know how protective they are or how long the protection lasts.
  • A safe and effective vaccine still won't work in everyone who gets it, so we can't conflate vaccination coverage with immunity, WHO's Dr. Bruce Aylward said.

Recent reports have suggested that herd immunity may be achieved when as little as 50% of the population is immune. Herd immunity occurs when enough of the population is immune to the coronavirus, either via exposure or vaccine, for transmission to wane.

That's a welcome projection in light of earlier estimates that at least 70% of the population would need immunity before we'd be at "herd" level.

But these estimates are largely irrelevant and a distraction from the tools experts know work in combatting the coronavirus's spread, World Health Organization officials said during a media briefing Monday.

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"Right now, as a planet, as a global population, we are nowhere close to the levels of immunity required to stop this disease from transmitting," Dr. Mike Ryan, the executive director of the WHO Health Emergencies Programme, said.

"We need to focus on what we can acutely do now to suppress transmission and not live in hope of herd immunity being our salvation."

We don't know how long protection from the virus lasts after infection

One way to develop protection from the coronavirus is to survive it or be exposed to it, which can lead you to develop antibodies that fight against the virus.

But while experts do know such a response exists, they don't know how strong it is, how long it lasts, and how it may vary between people.

Even if the presence of COVID-19 antibodies meant you were shielded against the coronavirus, research indicates only about 10% of the global population has these antibodies.

"That means that a large proportion of the population remains susceptible to infection, and that means the virus has an opportunity to spread," infectious disease epidemiologist Maria Van Kerkhove, WHO's COVID-19 technical lead, said during the briefing.

In other words, we're a long way from herd immunity via antibodies.

Even when a vaccine becomes available, it won't protect everyone who gets it

The other, and superior, way to protect yourself against the coronavirus is to get a vaccine. But a safe and effective one is not yet available.

Once a vaccine is available, it won't work in a subset of everyone who gets it. "We can't confuse vaccination coverage with the proportion of the population that's immune," Dr Aylward is the Senior Advisor on Organizational Change to the Director-General

That means establishing herd immunity through vaccinations requires more people to get one than whatever percentage of population-level immunity is needed to defeat the virus.

"In a situation like this, where we locked down half the world's population, where the economy has ground to a halt in so many places, you have to plan for very high levels of herd immunity because we don't want to take chances, we don't want to be wrong," Aylward said.

Companies and governments responsible for rolling out vaccines, he added, shouldn't "get lulled into a dangerously seductive suggestion that [the levels needed] could be low."

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Dr. Mike Ryan. Image: Reuters

What citizens and their leaders should do is recognize that waiting until we've reached herd immunity "isn't a solution" to the pandemic, Ryan said.

The only solution is implementing all known-to-be-effective strategies — like testing, contact-tracing, isolating, mask-wearing, and physical-distancing — while continuing to collaborate globally on therapy and vaccine development.

"It's about getting all of these tools to scale," Aylward said, "so that we can actually tackle this thing properly and get back to the new normal we need to keep our societies functioning and our economies open and our health system safe."

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