What Is Herd Immunity, and Why Is It Important for COVID-19 Survival?
In the wake of the coronavirus pandemic, many experts have noted that herd immunity is what is needed for us to slow the COVID-19 infection rate and prevent the overwhelming spread of the disease. But there tends to be some misunderstanding about what herd immunity actually entails. On its most basic level, herd immunity is achieved when a high enough percentage of a population has become immune to a virus, making it very difficult for that pathogen to spread from person to person. Trying to create herd immunity, though, is where things get complicated.
As it turns out, there are primarily two ways to achieve herd immunity. The first is that a large enough percentage of a population must contract a disease and either die from it or develop immunity to future infections after surviving the illness — preferably the latter. The second is that pharmaceutical companies produce a vaccine that is distributed to at least 70 to 90% of the population, and that vaccine makes them immune to the virus for a period of time.
How Herd Immunity Ended the 1918 Spanish Flu Pandemic
How helpful is herd immunity, exactly? It’s in part what ended one of the most famous pandemics in recent history: the Spanish flu pandemic of 1918. At that time and for the next year or so throughout the demobilization process, soldiers were returning home from WWI, and this movement largely contributed to the spread of the virus around the globe. The Centers for Disease Control and Prevention (CDC) estimates that at least 50 million people died due to this pandemic, and the H1N1 virus that caused the Spanish flu is believed to have infected 500 million people globally — a third of the world’s population at the time. This widespread nature of infection — the fact that so many people contracted the virus and had to either heal or pass away from it — was enough to create collective immunity to the virus. Interestingly, the virus has never gone away completely; remnants of the Spanish flu are still found in modern strains, even though vaccines increase our immunity to it.
Can We Prevent the Same Loss of Life Now?
In today’s climate with the novel coronavirus continuing to spread rapidly, health experts are attempting to avoid the same massive loss of life the world experienced a century ago. In the case of that Spanish flu pandemic, herd immunity was achieved in two years, but it’s important to remember that it also caused many people to die in the interim. Medical professionals and health organizations are aiming to prevent such large-scale mortality and spreading of the virus — we have the know-how to do so this time around, despite much remaining unknown because of the novel nature of the coronavirus.
Vaccines and Herd Immunity
A likely pathway to herd immunity for COVID-19 comes by way of vaccines, which is how we’ve created immunity during recent history with infectious diseases such as mumps, chickenpox, polio and measles. Unfortunately, and not until recently, outbreaks of these diseases have started to occur in communities with high levels of anti-vaccination sentiment among their populations. We've already seen this with measles in the United States. The virus was declared eradicated there in the year 2000, but anti-vaccination sentiment grew in the years following that, resulting in some populations having high under-immunization rates. In 2019, 1,250 cases of the vaccine-preventable disease were confirmed across several states.
What If People Don't Get Vaccinated for COVID-19?
In locations where populations get vaccinated at high rates, a community achieves herd immunity and can eventually eradicate the disease. If a large enough percentage of the population gets the COVID-19 vaccine once it becomes available, there won't be a high enough number of nonimmune people who can spread the virus at high rates. This can keep unvaccinated people safe. We won’t know for sure if enough people get vaccinated until the vaccine becomes available. If a high-enough percentage of the population decides they’re not willing to get vaccinated, the coronavirus can continue to spread, particularly if people stop practicing social distancing or wearing masks.
What Does Slowing the Spread of COVID-19 Involve?
Until a vaccine is developed, it’s essential to continue doing all we can to slow the spread of the coronavirus. This will prevent us from overtaxing hospital systems and medical resources — and it will save lives. If we sought to achieve herd immunity by virus exposure alone, it would likely mean tens of millions of lives lost and would not guarantee eradication of the virus. The good news, however, is that social distancing, wearing masks, washing hands frequently and taking other similar steps gives us the chance to slow the spread while scientists research and develop a potential vaccine. Both a vaccine from pharmaceutical company Pfizer and another out of Oxford University may be ready by the end of the year. The more our population can slow the spread of the virus until a vaccine is deployed, the more unnecessary loss of life we can prevent.