Herd Immunity and COVID-19

Written by Siya Vashi

Herd immunity occurs when a specific percent of the population (the herd) is immune to a contagious disease, be it through previous infection or vaccination. Herd immunity is especially important when faced with an outbreak, a prime example being COVID-19. 

To calculate roughly what percent of the population must be immune to a specific disease, this equation can be used: 

The variable here is R0, which is also known as the basic reproduction number. This tells the transmissibility of an infection. For example, the basic reproduction number for COVID-19 was calculated to be around 4.22, with a margin of error of 1.69. This means that an infected COVID-19 patient, on average, spread their infection to roughly 4-5 people. If we use these numbers in our formula, we can calculate the herd immunity percentage to vary from 60.5% to 83.1%. This means that in order for a COVID-19 outbreak to stop, 60.5%-83.1% of the population must be immune to said infection. 

The easiest way to do this was to create a vaccination rather than waiting for over half of the world to develop immunity to COVID-19. Now, in the US at least, people are much less likely to get COVID than before because about 70% of the population is fully vaccinated. Of course, it’s common sense that more vaccinations mean less disease. But the important part of herd immunity is that it tells us how many people do not have to get vaccinated. Babies, the elderly, or those with certain health or religious conditions are just a few examples of people who should not get vaccinated. Herd immunity is a way to protect these people from contagious infections, which is why it’s important for those who can be vaccinated to do so. It can save not only your life, but other people’s lives as well. 

References 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7359536/#:~:text=Our%20mean%20basic%20re production%20number,outbreak%20in%20Wuhan%20%5B33%5D. 

Written by Siya Vashi from MEDILOQUY