On Dec. 31, 2019, the World Health Organization’s (WHO) office in China noted a report of cases of “viral pneumonia” on the website of the Wuhan Municipal Health Commission. Earlier that same month, there was another important milestone: at its headquarters in Geneva, the WHO celebrated the 40th anniversary of the confirmation of the eradication of smallpox. As more and more people receive vaccines and with steep declines in the number of COVID-19 cases worldwide, what does the end of this pandemic look like? Will we also win freedom from this virus?
Elimination Versus Eradication
This Holy Grail of infectious disease control, eradication, refers to a permanent reduction to zero in the number of new cases of an infectious disease worldwide. The enormous advantage of eradication is that control measures for the disease are never needed again. The word elimination is used to describe a situation when the number of new cases of disease is zero, but only in a defined region. Indeed, the CDC was originally established in 1946 to eliminate malaria, which was achieved by 1951. Campaigns launched in response to specific pathogens can often have profound and lasting impacts on public health more broadly.
Both elimination and eradication entail non-sustainable campaigns in which expenses and resources are front-loaded to definitively suppress the disease. Through lock-downs, widespread physical distancing, travel restrictions, mask wearing, and urgent vaccine efforts, most countries that are in position to do so have already embarked on the initial stages of a COVID-19 elimination campaigns, even if that is not regarded as a goal. The question is not whether to launch the campaigns but how long to sustain to them.
Can COVID-19 Be Eradicated?
Most experts believe the answer is no and predict that the virus will continue to circulate indefinitely, transitioning from the current pandemic to a steady, but much lower, endemic rate of infection. Such pessimism is not unlike the views of many prior to the eradication of smallpox. In 1965, René Dubos, perhaps the most well-known microbiologist of his time, wrote in Man, Adapting, “Eradication of microbial disease is a will-o’-the-wisp; pursuing it leads into a morass of hazy biological concepts and half-truths.” His view is perhaps a cautionary tale as to why we should not so readily dismiss the possibility of eradication. While assessments on the feasibility of eradication tend to focus on the biology of the pathogen, the infection it causes, and the vaccine effectiveness, it’s important to consider many broader factors such as the capacity of the public health system, and, perhaps most importantly, the sociopolitical realities that will dictate the available resources, length, and scope of any efforts.
At the level of the pathogen, there are several properties that make any infectious disease more or less amenable to control. Only one, however, precludes any attempt at eradication, and that is if there is a significant reservoir where the agent can survive outside of humans on an indefinite basis and from which humans can acquire infection. For COVID-19, there is little evidence to date that this is the case. If we can sustain an interruption in the transmission of this virus among a sufficient number of humans, we could eradicate COVID-19. Can the vaccines achieve this? The evidence is early and incomplete at this point, but the mRNA COVID-19 vaccines do appear to provide impressive levels of protection against infections.
Of course, effective vaccines will not be helpful unless we can rapidly get them into large number of arms all over the world. The main challenge here will be in supplying enough doses, especially to those in resource-poor settings, to achieve herd immunity. The current COVAX initiative to provide equitable global access to COVID vaccines has committed to providing doses for at least 20% of a country’s population. Billions more will be needed.
What about viral variants? If the virus mutates in such a way that the available vaccines are no longer protective, one future scenario with COVID-19 is akin to seasonal influenza in which the infection becomes endemic, circulating throughout the globe in waves of infections requiring regular re-vaccinations of variable efficacy in a Sisyphean response to emerging variants. The development of variants, which can only occur when the virus replicates, is one compelling reason to pursue more aggressive suppression measures. Unlike previous vaccines, the new coronavirus vaccines are much more amenable to rapidly catching up with new variants as they emerge. The current vaccines were developed in as short as eight months; the availability of vaccines adjusted to protect for variants is really only limited by the time to manufacture and secure authorization using these platforms.
Viruses generally weaken or attenuate to become less virulent over time, and there is intriguing evidence that our current coronaviral pandemic may not have been our first. Since the 1960’s, we have identified four coronaviruses that are endemic to humans. While these coronaviruses collectively are considered to be the second leading cause of the common cold, they have the potential to very rarely cause much more serious respiratory disease similar to COVID-19. An 1889 pandemic attributed to influenza may actually have been the result of a then-novel coronavirus in humans that spilled over from a nearly identical strain found in cows. If correct, this coronavirus subsequently weakened to become one of the four current strains endemic to humans. The massive investment necessary to achieve elimination or eradication would clearly not be justified for the common cold.
What Will It Take?
Smallpox eradication was not achieved by simply vaccinating a sufficiently large proportion of the population to achieve herd immunity. The twofold lessons of smallpox eradication are that, while we don’t need to vaccinate everyone, we must have robust public health systems for case surveillance, including testing and contact tracing in the later stages.
The experience in many countries, including the U.S., has been that these systems are not up to these tasks, due to decades of underinvestment in public health. Essential public health functions were rapidly overwhelmed, suffering from poor compliance and ultimately failing to prevent the spread of disease. The irony is that powerful tools are now widely available that can be accessed for case surveillance. Cell phones, data from electronic transactions, and surveillance camera footage have all been successfully implemented to comprehensively trace COVID-19 contacts in South Korea and effectively limit spread. The challenge for other countries is to address legitimate privacy concerns and achieve the broad societal support.
Successful elimination programs have taught us that the use of all available measures is the only way to achieve control. For COVID-19, widespread mask wearing, hand washing and physical distancing measures will all complement the vaccines in reducing viral spread. Indeed, these measures have been so effective that several countries, most notably New Zealand, but also Vietnam, Brunei, and several Caribbean nations have successfully reduced the number of new community-acquired cases to zero for prolonged periods of time. In essence, COVID-19 has already been successfully eliminated even without the use of vaccines.
Are We Willing Make the Investment?
Comprehensive implementation of these measures will require an enormous global shift of money and resources from the rich to the poor and sustained, high-levels of collaboration and cooperation that may be beyond us. Ultimately, a decision to get to zero COVID-19 may come down not to determining if it is possible to eliminate or eradicate this virus but if we are collectively willing and able to work together and if it is worth such an investment. The cost is enormous and paid at the outset, but for a long-term benefit that is infinite and incalculable. Wouldn’t it therefore be wonderful to prove Dr. Dubos wrong… again?
Christopher Martin, MD, MSc, is a professor at the West Virginia University School of Public Health and director of the Health Sciences Center Global Engagement Office.