What You Need to Know about Herd Immunity and COVID-19
With the coronavirus continuing to spread around the globe, researchers and health experts are on the hunt for a way to curb the spread of the virus and develop a vaccine or find a treatment. Developing a safe vaccine takes time, however, and a realistic COVID-19 vaccine is likely at least a year away, if not longer. In the meantime, health experts have considered the idea of antibody tests to determine if relaxing social distancing measures even more can be safely done. These tests can show who has antibodies in their blood for the coronavirus and who doesn’t, therefore theoretically helping identify who has and has not been exposed.
Antibody tests have been performed in a few places already, including California. What these tests are showing is that more people have been exposed to the virus than anyone realized. Experts hope that those who have been exposed develop immunity to the virus, but we do not yet know for sure if this is true, or if it is, how long it lasts.
With all of this going on, you have likely heard the term herd immunity being tossed around as a way to stop coronavirus. So, what is herd immunity, and how might it impact the way we are handling COVID-19?
Understanding Herd Immunity
In its most basic form, herd immunity (sometimes also called community immunity) occurs when a large portion of the population becomes immune to a particular disease within a specific area. Even though not every person in the area is immune to the disease, the entire group stays protected; when there are fewer high-risk individuals, such as babies or immunocompromised people, and more resistant individuals, eventually the illness has nowhere else to go and peters out. Herd immunity helps to protect these high-risk individuals, who cannot fight the illness off on their own.
Can We Create Herd Immunity?
Herd immunity occurs through two main avenues: naturally and with the help of a vaccine. When it occurs naturally, your body creates antibodies after you’ve been exposed to a particular virus. These antibodies can fight off the virus if it returns.
An example of herd immunity happened recently during the Zika outbreak in Brazil. After two years, 63 percent of the population had developed antibodies after exposure to the virus, helping stop continued outbreaks.
The other option for herd immunity is to create it artificially through a vaccine. Vaccines work by making your body think it has been exposed to the virus or bacteria that causes the disease in question. Your body starts to create the necessary antibodies to fight off the illness without having to get sick first.
Achieving herd immunity through a vaccine or natural immunity requires different numbers of people to become immune depending on the reproduction number, also known as R0. This number will let you know the average number of people that can become infected by just one person if they aren’t already immune to the disease. As this number rises, so does the number of people that need to have immunity before herd immunity is achieved.
Reproduction Number and COVID-19
Most researchers place the R0 of COVID-19 between 2 and 3, which means that one infected person can infect about two to three other people if they aren’t already immune. What that also means is that probably at least 50 percent of the population would need to be immune for herd immunity to kick in, and it might be as high as 67 percent.
There is another factor at play concerning COVID-19 and herd immunity. Though herd immunity for certain diseases like measles, chickenpox, and mumps has made these diseases relatively rare (through the use of vaccines), other viruses are prone to mutation, which makes the situation more complex. The most well-known incidence of that mutation is the seasonal flu (influenza). Antibodies created to fight influenza only provide immunity for under a year, which is the reason we get annual vaccines for the flu.
If this particular type of coronavirus (SARS-CoV-2) is like other coronaviruses that we currently know can infect humans, any immunity would likely last a few months to a few years. What’s quite unlikely is that immunity would last as long as a person’s lifetime. The problem is that right now, we don’t know how long any supposed immunity lasts.
Though some people are suggesting that intentional exposure could help herd immunity develop faster, the reality is that among vulnerable populations, COVID-19 is more dangerous than other similar illnesses, such as the flu. This approach would likely result in more deaths numbering in the thousands or even hundreds of thousands. Even if the same number of people ultimately become infected with the disease, it’s better and more manageable for healthcare systems if these infections are spread out over a longer period.
We don’t yet know how immunity works with this particular coronavirus, and much more research is necessary to understand the disease better.
