Some thoughts on reopening
I recently did an interview for an article on herd immunity for the Huffington Post. The article is well done, and has a thoughtful discussion about what it will take to achieve herd immunity. This got me thinking about time frames, and what reopening means.
Essentially, there are two paths to herd immunity, which is the idea that enough people are immune to an infectious disease that new outbreaks can’t take hold. One path to herd immunity is vaccinating enough of the population; the other path is to have enough people become infected, and as a result, immune. The percentage of the population that needs to be immune to achieve herd immunity differs based on how many people become infected by each case of the disease.
This idea of reducing the number of new people infected by each new case of Sars-Cov-2 can be done without herd immunity, but it’s painful — decreasing the number of new infections is the driving force behind the social distancing, limiting crowd size, closing schools, and all these other “non-pharmaceutical interventions” that every country has had to wrestle with over the past couple of months. In fact, these interventions allow us to achieve what I’m thinking of as “effective herd immunity” — outbreaks can’t take hold in communities where each new case does not result in more new cases, even when not all that many people are immune. Maintaining some degree of social distancing measures even as things reopen maintains our effective herd immunity. The challenge is exactly how much social distancing is needed.
The idea of achieving herd immunity through letting many people get infected is hard to imagine. There are 4 million known cases in the world, and many more times that number of cases that have not been officially diagnosed due to lack of testing, not seeking care, or false negatives. BUT there are 7.8 BILLION people in the world. Even if 40 million people, or 400 million people, have already been infected that is a whole lot of new infections and associated deaths, illnesses, and as yet unknown long term consequences of infection.
That leaves us with 1) waiting on a vaccine and 2) managing until we have a vaccine.
Being in the “managing until we have a vaccine” phase as we are, the question for reopening is how much can we get away with in terms of activity and interactions before we reverse the gains of non-pharmaceutical interventions. This is essentially a grand scale experiment, with different states and countries trying different variations and the outcomes becoming clear weeks and months later as rates of hospitalizations and deaths become clear. The problem is that the tools we need to manage well are not fully yet available or fully vetted in many cases, including scaling up testing, understanding immunologic and population-level implications of antibody testing with the hodgepodge of tests currently available, building up a contact tracing workforce, understanding best practices about maintaining infection control in a region and in different industries, effective early stage treatment, and effective real-time population surveillance to detect new waves of infections before large numbers of people come into the hospital very ill. In the U.S., unrestricted travel between areas with strict and less strict measures are going to present a particular challenge.
One point that stuck with me when I studied lead poisoning in children is that the default situation in the absence of effective public health measures is essentially using the kids as barometers of the lead levels in their environments. Widescale reopening in the absence of *effective* public health measures to quickly detect and contain new outbreaks is essentially using infections in the most vulnerable populations — those who work with the public, residents of institutional settings like nursing homes and correctional facilities, communities where crowding cannot be effectively addressed — as a barometer for how well we’re doing.
From what I have read about vaccine development (not my area of expertise by any means), it is such a long, complex, and uncertain process, particularly against a coronavirus, that even with so many of the world’s scientific resources focused on this area, that the process to a certain extent takes the time it takes, and the 18 month to 2 year timeframe that has been frequently reported reflects the most realistic timeframe for a full vaccination campagin to take place, even with all the current efforts underway.
As restrictions are lifted, we are not again going to be in the same situation we were two months ago, with nearly no testing, few precautions in place, and a limited understanding of how disease spread occurs. We are not, however, in much of a different situation in terms of how many people could become infected and seriously ill with unrestricted or ineffective social distancing until more effective tracking efforts and population surveillance tools are developed and deployed. As more businesses open and more types of interactions are available, we are all going to have to decide on our risk tolerance, and how much we expand our “social bubble” to let in additional people. Reducing the risk of infection for the immediate future is still going to be best achieved by limiting the number and intensity of interactions with other people.
