There has not been much change in the amount of COVID-19 spread in our area over the past week. It continues to spread at a steady (and relatively high) rate with 34 new infections identified in Wright County from last Thursday to this Thursday. Four Wright County residents remain hospitalized, with two of these hospitalizations being new this week.
A concept that many may have heard about during the COVID-19 epidemic is the idea of “herd immunity.” I’d like to clarify what herd immunity means and how this applies to the current crisis. This is a complex topic and it requires some explanation, so I’ll do my best to simplify, but if anyone wants the short and simple version, just jump down to the underlined part. Also note that this isn’t intended to be any statement about what we should do, but an explanation of what herd immunity is and an honest assessment of our best understanding of what it would take to get to herd immunity through natural infections.
Herd immunity is a concept that originally comes from public health vaccination efforts and describes how many individuals have to be vaccinated before even the unvaccinated people are protected. Why would even unvaccinated people be protected? This is because for a disease to keep spreading, even currently infected person needs to infect at least one other person (on average). If it is less than that, the disease will gradually die out in that area. As an illustration, say someone has COVID-19 and is in close enough contact to cause infection with 3 other people during the time they are infectious. If all 3 of those people already have immunity to COVID-19 through vaccination or natural infection, that particular person isn’t going to contribute to ongoing spread of COVID-19.
Much of the current conversation around herd immunity comes from a suggestion that we should have younger healthier people do all their normal activities without any precautions while keeping those who are more at risk from COVID-19 isolated until “herd immunity” has been reached and everyone can go back to their normal lives. We all want to go back to our pre-COVID lives and I’ll be the first to admit that there are still many things we don’t know about COVID. However, it is also important to acknowledge what we do know and what is likely to happen if we try to reach herd immunity solely through natural infections.
The summary is this - reaching herd immunity through natural infections will lead to a lot more severe illness and deaths.
Here are the main reasons why:
- It is practically very difficult to keep older or otherwise vulnerable people separated from healthier people who are at lower risk. This would be much easier if COVID-19 could only be transmitted by people with symptoms, because then anyone who had symptoms could just stay home. But, we know that COVID-19 can be transmitted by people before they have symptoms. In addition, we all know that there are people still working into their 60s that are going to have close contact with others through their work or older parents/grandparents that will want to be around their families at the holidays.
- For herd immunity to work, the immunity has to be durable. Unfortunately, the immunity to most infectious organisms is not permanent. We do not yet know how long typical immunity to COVID-19 lasts, but we do know that antibodies to the COVID-19 virus can decrease within a couple months. Immunity to other viruses in the coronavirus family typically lasts around a year. So, while a natural infection may give temporary immunity, the previously infected person could still pick up and transmit the infection to a higher risk person later when their immunity has diminished. If this loss of immunity occurs similar to other coronaviruses we will never reach true herd immunity naturally. Vaccinations can be designed to teach the immune system to recognize an infectious organism for longer than natural infection would, which is part of why the entire concept of herd immunity really comes from studying vaccines.
- Third, we’d have to get a lot more people infected to get to the point where there’s even a chance of having true herd immunity. We do not know exactly how many people have been infected with COVID-19 so far or exactly what percentage would need to be immune to reach herd immunity, but we do have some reasonable estimates that tell us we’d still have a long way to go. In Wright County 708 people are known to have been infected with COVID-19. Even if we assume that this is only 1/3 of the real number of infections (because some were asymptomatic or simply didn’t get tested) that means 2124 people out of an estimated 12,690 people in the county have been infected and could have immunity (16.7%). The best estimates we have (primarily from our understanding of viruses transmitted in a similar way) indicate that 60-70% of people would have to be immune to reach herd immunity. We can be confident it isn’t as low as 10-20% some have suggested because many places have already reached that level and COVID-19 infections haven’t died out in those areas. Though there are important differences in how people contact each other, another useful example is what has happened at the San Quentin Prison in California where more than 60% of the population was infected before spread was halted. To get from 16% to 60% we’d need to have over 5000 more people in Wright County infected.
- Finally, COVID-19 continues to be a potentially severe illness. We know these aren’t going to be perfect predictors but the best current estimate from the CDC is that 1 of every 200 infected people age 50-69 and 1 of every 18 infected people over 70 will die of COVID-19. In Wright County, we have had right at 100 people over the age of 60 known to be infected with COVID-19 and one of those individuals has died, so our local experience has been fairly in line with those estimates.
There are many different and valid opinions about how we balance the risks of COVID-19 with the burden of social distancing precautions that affect all of our lives, but hopefully some understanding of what herd immunity is and what it would take to achieve helps to have honest conversations that acknowledge reaching herd immunity in a natural way is likely to lead to a lot more severe illness and a significant number of deaths.
