Although the number of cases of COVID-19 continue to rise in the United States, restaurants and schools are beginning to open, and many people are acting as if the pandemic is over. Supporters of opening businesses and schools state that we cannot continue isolating ourselves, and that we need to build up our immunity. So, can herd immunity really be achieved in this pandemic? Can it be the solution we have been waiting for?
Considering how no one was immune to this virus when it first emerged, there was a very rapid spread of the disease. According to the Johns Hopkins Bloomberg School of Public Health, herd immunity is achieved when most of a population is immune to a disease. This immunity indirectly protects those individuals who do not have immunity to the disease. While it varies depending on how contagious a disease is, on average, 70 to 90 percent of the population needs to be immune for the population to achieve herd immunity.
Herd immunity can be achieved when a high percentage of the community is immune either from previous infection or from a vaccine. With vaccines, those who are immunocompromised or too young to receive vaccinations are protected through herd immunity. In the United States, smallpox and polio have been eradicated due to vaccines, and those unable to receive vaccinations have been protected from the disease due to herd immunity. The development of a vaccine is the most optimal approach to achieving herd immunity. With this method, immunity would be achieved without further infections and complications due to the disease.
Fortunately, a phase 3 clinical trial of a potential vaccine for prevention of COVID-19 has begun as of July 27, 2020. A phase 3 clinical trial occurs after the safety and effectiveness of the medication or vaccine is investigated in a small population, along with its side effects and risk factors. The phase 3 clinical trial involves a larger group of participants so that researchers can better understand the medication or vaccine’s effectiveness and side effects. The trial for the vaccine, which is called mRNA-1273, will be conducted at U.S. clinical research sites, and will involve 30,000 adult volunteers who do not have COVID-19. Since the vaccine has already proved to be immunogenic, this trial will also attempt to determine how long protection from the vaccine will last. While this is a potential solution to the pandemic, it will not be plausible for at least several months, even if the trial is successful.
Herd immunity can also be achieved when a large number of people have been infected by the disease, recovered, and then developed antibodies, which protect them from future infection. This type of herd immunity was seen in the 1918 flu pandemic. With COVID-19, it is not clear whether this time of immunity is a plausible solution. Since it is such a new disease, it is not clear whether everyone who has recovered develops antibodies, and how long those antibodies last. There have also been potential cases of reinfection.
Even if being infected with COVID-19 leads to the development of long-lasting antibodies, a large percentage of the population must be infected in order to reach the threshold of herd immunity. This is far too risky, especially when considering how more vulnerable populations are more likely to have severe complications from the disease. Far too many infected people would die in an attempt to reach the threshold of herd immunity via natural immunity.
Since there would be far too many deaths with this method, herd immunity achieved with the development of a vaccine is a much better potential solution. However, since there likely will not be a safe, tested vaccine for several months, we must continue following recommended safety guidelines and precautions. Social distancing, wearing masks, and frequently washing our hands is what we must continue to do in order to prevent further spread of the disease before a vaccine is fully tested and developed.