In 1980 the World Health Organization declared smallpox eliminated, a long 21 years after the start of the eradication program. Initial steps focused on mass vaccination in a quest for herd immunity. In developed countries with robust infrastructure, this proved relatively straightforward. This was not the case for developing countries with large numbers of hard-to-reach villages. Once most of the world’s population was immunized, the eradication program switched its focus from a quest for herd immunity through vaccination to early identification of every smallpox case. Once discovered, rapid deployment teams mobilized to the area to immunize everyone within miles of the infected individual. In addition, they traced and then vaccinated all persons, and their contacts, who recently visited the index case. As smallpox has no animal host, eradication of the disease in humans removed the threat of the disease forever.
So, what can we learn from the battle to eradicate smallpox that can be applied to the current pandemic? Although achieving herd immunity is critical to ending the pandemic, it makes sense to look at this task regionally, rather than by country or state. Once healthcare workers, first responders, and high-risk individuals have been vaccinated, officials should focus their vaccination efforts on the general population in regions exhibiting the greatest spread of the disease. Vaccinating individuals in these areas will slow disease spread, and over time create a bubble of herd immunity.
In areas with a large number of previously infected individuals, there will be an existing base of people who will have natural immunity. When combined with those being vaccinated, the region may reach an effective level of herd immunity even before 80-90% of people are vaccinated, the estimated level thought to be necessary to achieve true herd immunity.
As these “bubbles” grow and overlap other bubbles, areas of herd immunity will begin to cover ever larger geographic regions creating, relatively speaking, a “COVID-19 safety zone.” If properly targeted, this will afford us additional time to administer vaccinations by limiting the spread of COVID-19 and its associated morbidity and mortality.
Unlike today where disease spread is out of control countrywide, this targeted vaccination strategy will create regions of the country where infection rates will be low enough to allow businesses to reopen and to do so sooner. Testing and tracing will continue to be an important factor in understanding where the virus is spreading and inform public health officials on which areas to concentrate their vaccination efforts.
Sure, in a world with unlimited vaccine supply and perfect vaccine administration processes, this targeted vaccination program is not necessary. But we are not living in that world right now. Therefore, we need to think of innovative ways to expand our efforts to stop disease spread while vaccinating our citizens to obtain herd immunity. Taking lessons from the smallpox eradication effort is a logical path for our public health officials to consider.