Let’s start with the fact that “herd immunity” is actually not terribly well defined. The definition is pretty clear, enough incidence of infection and vaccination that the spread of disease becomes unlikely. The issue for many is there is not necessarily a precise percentage we can attach here. That is actually fine, I am sure for different diseases the threshold for herd immunity would be different. However in the current situation with COVID-19 we are trying to vaccinate quickly to help get to this level. Depending on the definition this is going to be an interesting policy question.
I provide the ND population pyramid (for 2019) to help make this point. The distribution of the population across the age ranges can make achieving herd immunity difficult. Let’s say the number we need to achieve is 70%. That is, 70% of the population needs to either catch the disease or receive a vaccine. This is lower than some of the numbers thrown around at times (80% was one I saw several times). Even at 70% this looks challenging for North Dakota.
Part of the issue is that vaccines are, at this time, only approved for 16 and over. Moderna announced this week they are trialing their vaccine with children and, as I am about to demonstrate, that is a must for further returns to normalcy. In 2019, 79.1% of the population in North Dakota is 16 or older, making the margin for error very low to start. This 9.1% of the population turns out to be approximately 69,348 people. So if 70,000 people over age 16 decline to get vaccinated and do not contract COVID we would not reach the 70% goal.
In early February various news outlets reported about 1 in 3 will not get the vaccine. If that rate were to hold in the 16+ population in North Dakota we would fall well short of a 70% target from vaccination and would rely on either infection rates to push us to the threshold or to not reach it and worry about outbreaks. Of course this would also likely necessitate further mask mandates and other restrictions which are already very unpopular.
I will unpack some more about this in a later post.