What is Herd Immunity, and How do We Get There? Photo: iStock

What is Herd Immunity, and How do We Get There?

Herd immunity is the idea that if a majority of people in a population have immunity against a certain disease, the disease can no longer spread. After the discovery of vaccines, we were able to inoculate enough people against smallpox that the plague became virtually extinct. But will we be able to sentence COVID-19 to a similar fate?

We Need Antibodies!

When a virus or bacteria invades your body, your immune system mounts an attack on the foreign invaders. There are two types of attack: a non-specific response, and a humoral (or specific) response. It’s the latter that can help bring about herd immunity in the long-run. If enough people in the population have COVID-specific antibodies, the virus would be unable to replicate, infect, and spread. Of course, no one would advocate for getting everyone sick just so they could develop antibodies.


Smallpox was a plague on humanity for thousands of years. The costs of smallpox were facial scarring, and likely death. This means that if a smallpox epidemic swept through a village, about 30% of the people would die and the rest (65% – 80%) would be left with deep, pitted scars on their faces. Naturally, forcing people to develop antibodies by exposing themselves to smallpox was neither a safe nor effective way of bringing about herd immunity. Similarly, scientists will have to find a way of immunizing people against COVID-19 without making them suffer from the disease.

Not All Antibodies Are Long-Lasting

While some diseases can’t afflict the same person twice, that’s not true of all maladies. While the verdict is still out on whether COVID-19 antibodies can become permanent, the picture looks bleak. There have been an alarming number of re-infection cases during this pandemic, with some studies showing that antibodies don’t circulate in the blood for more than a month or two. This is drastically different from other diseases where antibodies are detected for years after infection. All of this means that simply overcoming a case of COVID-19 doesn’t necessarily protect you in the future.

From the Cow

The best way to achieve herd immunity is through vaccination. The story of vaccines begins with an observant scientist named Dr. Edward Jenner. He noticed that milkmaids who were infected with non-lethal cowpox seemed to be resistant to smallpox infections. He tested his theory on a 9-year-old-boy who had been exposed to smallpox. The boy never developed disease, proving Dr. Jenner’s hypothesis correct. Thus, the first vaccine was discovered. In fact, the word “vaccine” is actually an ode to its cattle origins. It comes from the Latin word “vaccinus” which means “from the cow.”

Everyone Has To Be On the Same Page

Today, most scientists have concluded that the only way to end the COVID-19 pandemic is by developing a vaccine. But reaching herd immunity will depend on everyone’s willingness to understand what a vaccine is, and to actually take one. With the rise of the “Anti-Vax” movement in recent years, and with widespread mistrust of scientific experts even at the top of our government, it’s possible that swaths of Americans will refuse to take the eventual vaccine. This means that we may never reach herd immunity from the coronavirus even with a vaccine. Further loss of life could ensue.