Herd Immunity Can Stop the Spread of a Virus, But It May Not Be Possible for COVID-19

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From the start of the COVID-19 pandemic, scientists stated that one way to defeat the virus would be to achieve herd immunity.

Now many are questioning whether COVID herd immunity is even possible.

The concept of herd immunity is simple: When a high percentage of a population is immune to an infectious disease,either through medical treatment or after recovering from an infection, it provides indirect protection to the entire population. When the virus cannot jump quickly from person to person, the spread slows down and, eventually, the virus ceases to be a threat.

Epidemiologists Gypsyamber D’Souza and David Dowdy, writing for the Bloomberg School of Public Health, explain herd immunity in this way: They note that in some parts of the world, more than 90% of children have received medical treatments to prevent diseases such as polio, measles, mumps and rubella by their second birthday. This level of immunity provides protection to the population as a whole, even to those who are not immune, “by decreasing viral circulation and the chance someone who is unvaccinated will encounter the virus.”

If a person with measles were to arrive in such a society, nine out of every 10 people that person could infect would already be immune, they explained. This makes it extremely difficult for measles to spread.

Now, scientists say, herd immunity for COVID-19 is probably not going to happen because not enough people are getting medical treatments. There’s the added problem that the virus is mutating too quickly to be easily brought under control.

Infectious disease specialist Dr. Christian Ramers told NBC News that he believes the delta variant “changed everything” because it is much more infectious, it looks like it’s a little more severe, and has evaded preventive medical treatments.

Scientists at the Harvard T.H. Chan School of Public Health say that, unlike diseases such as chickenpox and measles, it now appears that COVID will not be eradicated through herd immunity. Instead, they said, the virus will become endemic, meaning that enough people will gain immunity that there will be less transmission and fewer COVID-19-related hospitalizations and deaths, even as the virus continues to circulate.

The true impact of COVID-19 on Africa is difficult to assess accurately. Many African nations have patchy surveillance, so statistics are hard to compile.

Wafaa El-Sadr, chair of global health at Columbia University, told The Associated Press that, while Africa doesn’t have the resources to fight COVID the way other parts of the world are doing, somehow Africa seems “to be doing better.” For months, the World Health Organization has described Africa as “one of the least affected regions in the world” in its weekly pandemic reports.

Scientists say there are several reasons for the relatively low impact the disease has had on Africa compared to other parts of the world. Africans are more resistant to the disease than are people in other parts of the world because Africans are younger. The median age in Africa is 20, compared with 43 in Western Europe. Africa also has lower rates of urbanization — making it more difficult for the disease to spread — and people on the continent tend to spend more time outdoors.

Devi Sridhar of the University of Edinburgh told The Associated Press that African leaders haven’t gotten the credit they deserve for responding quickly to COVID. She specifically noted Mali’s decision to close its borders before COVID-19 even arrived.

“I think there’s a different cultural approach in Africa, where these countries have approached COVID with a sense of humility because they’ve experienced things like Ebola, polio and malaria,” Sridhar said.