@my_np_jenna and I worked together on this post that goes over the basic concepts of herd immunity and how it relates to COVID-19! 🙌🏼
In a nutshell, herd immunity thresholds are based on the contagiousness of the pathogen in question. This is captured by the reproduction number (R0) of a disease, which estimates the average number of people that get infected per 1 originally infected person. So an R0 of 5 means that on average 1 sick person will give the pathogen to 5 others, making the outbreak spread rapidly. If you can get at least 4 out of every 5 people immune to this e pathogen, only 1 person would get the pathogen for each 1 originally infected person. This, in essence, stunts the growth of the outbreak. Reaching a point where, on average, every 1 infected person infects even less than 1 person will result in a declining outbreak. This percentage of the population that stunts the exponential growth of an outbreak is the herd immunity threshold.
Importantly, there are individuals in our communities that can’t get vaccinated or do not have access to a vaccine at this time. We tried to highlight the important role that everyone who can get vaccinated plays in protecting those who cannot – reaching herd immunity.
Finally, we go over specifics of herd immunity for COVID-19. Early estimates of the R0 (based on the common D614G strain that made up the majority of infections globally in 2020) were 2 to 3. This range places the herd immunity threshold between 50% and 67%. However, D614G is no longer the predominant strain and the new variants are estimated to have higher R0 values (increased transmissibility), meaning the herd immunity threshold is higher than before. Because transmissibility is changing with time, no one herd immunity threshold can be defined at this time. What is important is that we try to get to the highest percentage immune that we can.
Posted on Instagram on May 5, 2021.