There’s a lot to talk about this week related to COVID-19. Johnson and Johnson has released some of the information from the study of their vaccine, which works in a slightly different way than the Moderna and Pfizer vaccines already in use. Also, there is a welcome decrease in the number of infections across the country, the state, and locally. Particularly as more people are getting vaccinated, this raises the question of how we decide when to back off on some of the precautions that are being taken.
I’d like to focus on this last question and we’ll address the Johnson and Johnson vaccine more next week. It’s important to have some understanding of why infections are currently decreasing to better understand when we can back off on precautions. For the number of infections to decrease, on average the number of people infected by each person who has COVID-19 has to be less than one. If it’s more than one, the number of infections will go up (whether we do enough testing to detect them all or not is a secondary issue).
There are two main things that can keep this infection rate down:
#1) We can reduce the ability of an infected person to expose others. This is how masking, social distancing, and quarantining work. All of them decrease the chance that the infected individual’s respiratory droplets make it into anyone else’s airway.
#2) Increase immunity so that the people who do come in contact with infected respiratory droplets don’t get infected. This is how herd immunity works. Developing immunity from a safe and effective vaccine is preferable as it doesn’t involve anywhere near the risk of severe illness or death that a natural COVID-19 infection does.
The dilemma is that #1 and #2 interact with each other. Consider an example of a community with 100 people and one is infected. If 90 people are completely isolating from others and only 10 people are in contact with each other, the infection can’t infect more than 9 additional people before it dies out in that community. If 8 of those 9 people are already immune, masking and social distancing among that group will not have much benefit as there is only one person who could possibly still be infected and the likelihood of that person coming in contact with the infected person while they are infectious isn’t that high.
But what happens in that same community if the 90 people who have been completely isolated see that the infection rate is almost zero and all start to go about their usual activities at the same time? Now there are suddenly 91 at-risk people and the infection is likely to spread rapidly through the community.
The situation we have now in our community is similar (though obviously less dramatic). Many of the most at-risk people have not yet been vaccinated and continue to severely restrict their contact with others. The infection rate is much improved over the last two months but is still active enough that having those who have been isolating restart their usual activities without precautions would almost certainly lead to a large increase in cases and deaths.
Ultimately, we don’t know exactly how many people currently have immunity or at what point we’ll reach the degree of herd immunity that allows us to go back to “normal” but we do have some good clues. Other similar viruses typically take around 70% of the population being immune before they die out with everyone going about their normal activities (this number may be higher if new variants truly are more easily transmitted). To date, only a little over 13% of Wright County is known to have been infected with COVID-19. Even if the true number of infections is 2-3x that (which is a reasonable guess due to asymptomatic infections and people who don’t get tested when ill), that would make 26-39% of the population immune from natural infection. Vaccination is starting to add to the immunity from natural infections. As of today, 967 people (just over 7% of the population) in Wright County have had at least one dose of vaccination. If we take the best case scenario and pretend all of these people are two weeks past their second dose and have the full benefit of their vaccine, that would only leave a maximum of 46% of people immune (7% from vaccination and 39% using the higher estimate for the number of natural infections). That just isn’t enough to reach true herd immunity and have all the high-risk people in our community be able to feel safe doing what they want to do.
We all recognize that there has to be some balance of maintaining livelihoods, school, and other important things even with the risk of COVID-19 still present. Masking and distancing where possible help allow these things to continue while still mitigating risk to the community. As more and more of the highest risk population gets vaccinated (especially those over age 60) there will be much less risk of severe illness and death from COVID-19 and we’ll be able to start the process of moving towards “normal.” How quickly this is able to happen depends on how quickly vaccinations are able to be produced/distributed and how effectively current precautions drive down the infection rate.