Successfully Containing COVID-19 in Taiwan: Quasi Population Immunity
Amidst the global pandemic, strategies for containing the virus have varied worldwide. Natural herd immunity, while not much of an actual strategy, has been discussed as a way to stop the spread. However, an estimated 70 to 90% of a given population would have to be infected, which would most likely result in significant mortality. Since natural herd immunity is unfeasible under most circumstances, an article (the first link below) studied a form of population protection in Taiwan, using the term “quasi population immunity” to describe “temporary immunity […] at the population level.”
For months, the outbreak has remained under control in Taiwan without a widespread economic shutdown or physical lockdown. The relatively quick response of its government is largely credited to previous experience with the 2003 SARS epidemic and a 2016 flu outbreak, but to really understand how “quasi population immunity” happened, let’s take a look at the basic reproductive number, R0. In class, we learned that R0 = k * p, where k = the number of contacts an infectious person has and p = the probability of transmitting the disease to a contact. To prevent an infectious disease from spreading infinitely, k and/or p should be lowered enough so that R0 is less than 1.
Enforced quarantines, including for those entering the country, coupled with digitally-assisted contact tracing have been effective in lowering k in Taiwan. During quarantines, health monitoring is done every day with a phone call by public health worker and by self-reporting through text messages. In addition, a smartphone-based real-time locating system was set up to ensure no one left their quarantine location. Naturally, this raises a whole host of privacy questions if the government can set up such a tracking system without people noticing, but under the circumstances, I was not particularly concerned by the monitoring while in quarantine, nor have I talked to others who were.
On the other hand, aside from other non-pharmaceutical interventions (NPIs) such as physical distancing and hand/surface hygiene, public masking has been a key factor in lowering p. After asymptomatic transmission was reported, masks became required in public spaces, and the Taiwanese government essentially took over mask production and distribution to prevent shortages. It is important to note here that existing infrastructure played a major part in making this possible. For example, the Nationwide Health Insurance program, which covers more than 99% of the population, was used to help distribute masks: anyone with a health insurance card could to buy masks weekly at designated pharmacies. Compliance with mask regulations also depends on the general attitude toward public health; as is the case in several other Asian countries, Taiwanese are already used to wearing masks when sick, even if it’s just the common cold. The nature of the US makes it difficult to implement such an extensive mask production and distribution system, and being forced to wear them takes time to get used to, but both are things that can certainly be worked on in the future.
If natural herd immunity seems an unfeasible goal, strategies to create “quasi population immunity” can be used to control diseases before vaccine-based herd immunity is achieved. In Taiwan, enforced quarantines and contact tracing helped lower k, while wearing masks (among other NPIs) lowered p. Together, R0 was brought down to below 1 so that the virus is contained. Of course, all this would have been much harder without taking action early on, before the disease became widespread enough to warrant a total lockdown. Even if the world was caught unprepared this time, we have to learn from the experience to develop infrastructure that can effectively respond to emerging infectious diseases, and ensure that correct information about prevention measures reaches the public.
Sources:
https://doi.org/10.1017/dmp.2020.357
https://doi.org/10.3390/ijerph17093311
https://doi.org/10.1016/j.ijid.2020.09.1483