Herd immunity is phenomenon that’s essential for lasting human health, but its role in the COVID-19 pandemic is still unknown.
Herd immunity occurs when a large portion of the community, known as “the herd,” becomes immune to a specific disease. This makes it less likely for the disease to spread from person to person. As a result, the entire community becomes protected, even people who aren’t necessarily immune to the disease.
But how exactly does herd immunity apply to the coronavirus? It’s a question that experts are working diligently to understand.
How Does Herd Immunity Work?
In order for any disease to spread, a certain percentage of the population must be capable of getting the disease. This is called a “threshold proportion.” When the proportion of the population that is immune to the disease becomes greater than the threshold proportion for infection, herd immunity grows and the spread of disease declines. This is known as the “herd immunity threshold.”
However, the exact numbers needed to achieve herd immunity threshold vary by disease. The measles, for example, is a highly contagious illness. Experts estimate that 94% of the population must be immune to the measles to stop the chain of transmission, which is why the measles vaccine is a standard in early childhood.
There are two main ways to achieve herd immunity: vaccination and infection. The devastatingly deadly 1918 Spanish flu pandemic, for example, only ended when the virus infected so many people that widespread immunity developed after they recovered. Vaccination is the preferred method to achieve herd immunity since it’s safer and far less deadly. Smallpox, polio, and rubella are all deadly contagious diseases that have been successfully controlled through herd immunity via vaccination.
What Do We Know About Herd Immunity For COVID-19?
Scientists are still working to understand how herd immunity might develop for COVID-19. Their research hinges on one major question: how long do COVID-19 antibodies survive in the body? Antibodies develop after coronavirus infection to fight potential future cases of the virus, but if those antibodies disappear quickly, immunity to COVID-19 won’t be easy to achieve.
A new major study in Spain, one of the European countries most affected by the coronavirus, recently reported no evidence of widespread immunity to the coronavirus. In fact, the study found only 5% of 61,000 Spaniards tested positive for antibodies of the coronavirus. Another 14% of people who once tested positive for antibodies tested negative just weeks later.
“Immunity can be incomplete, it can be transitory, it can last for just a short time and then disappear,” Raquel Yotti, the director of Spain’s Carlos III Health Institute, explained.
Furthermore, the study concluded that “most of the population appears to have remained unexposed” to coronavirus, “even in areas with widespread virus circulation,” study commentators Isabella Eckerle and Benjamin Meyer said.
“In light of these findings,” the two continued, “any proposed approach to achieve herd immunity through natural infection is not only highly unethical, but also unachievable.” This leaves large scale vaccination as the only potential method to end the coronavirus pandemic and achieve herd immunity for the future.