Volume 373| Issue 6562| 24 Sep 2021
Vaccine nationalism and the dynamics and control of SARS-CoV-2
BY Caroline E. Wagner et al.
24 Sep 2021
Stockpiling and control
A triumph that has emerged from the catastrophe of the severe acute respiratory syndrome coronavirus 2 pandemic has been the rapid development of several potent vaccines. However, 18 months into the pandemic and more than 6 months after vaccine approval, wealthy countries remain the major beneficiaries. Wagner et al. model the consequences of vaccine stockpiling in affluent countries on disease rates in lower- and middle-income countries and the consequences for the eruption of new variants that could jeopardize the early success of vaccines. For countries that can readily access vaccines, it would be better to share vaccines equitably to lower disease burdens in countries with less access, reduce the cost of having to be constantly vigilant for case imports, and minimize virus evolution.
The COVID-19 pandemic has imposed massive public health burdens and economic costs, with more than 220 million confirmed cases and more than 4.5 million deaths globally so far. In some countries, the rapid deployment of safe and effective vaccines has reduced cases, hospitalizations, and deaths. However, many regions across the world have little access to doses, and infections are resurging. Furthermore, sustained transmission has led to the emergence of novel variants of the causative severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus with increased transmissibility, and against which vaccines may be less effective. Thus, understanding the effects of vaccine nationalism and allocation on the dynamics and control of SARS-CoV-2 is critical.
We extend recent models of SARS-CoV-2 dynamics to consider the number of cases and potential for viral evolution in two hypothetical regions, one with high access and one with low access to vaccines. This modified framework allows for variation in the strength and duration of natural and vaccinal immunity, which are aspects of the virus and host response that remain uncertain, thus enabling general explorations of a number of potential scenarios. To model the sharing of vaccines, we begin by only coupling the two regions through their vaccination rates. For different immuno-epidemiological scenarios of SARS-CoV-2, we examine the medium- and long-term dynamics in both regions as a function of the fraction of vaccines shared. Then, we couple the regions through immigration and introduce potential transmission increases due to evolution. We use this coupled model to explore local and combined infection numbers and clinical burdens, as well as potential viral adaptation.
In general, we find that stockpiling vaccines by countries with high availability leads to large increases in infections in countries with low vaccine availability, the magnitude of which depends on the strength and duration of natural and vaccinal immunity. A number of additional subtleties arise when the populations and transmission rates in each country differ depending on evolutionary assumptions and vaccine availability. Furthermore, the movement of infected individuals between countries combined with the possibility of evolutionary increases in viral transmissibility may greatly magnify local and combined infection numbers, suggesting that countries must invest in surveillance strategies to prevent case importation. Dose sharing is likely a high-return strategy because equitable allocation brings nonlinear benefits and also alleviates costs of surveillance (e.g., border testing, genomic surveillance) in settings where doses are sufficient to maintain cases at low numbers. Across a range of immunological scenarios, we find that vaccine sharing is also a powerful tool to decrease the potential for antigenic and transmission evolution of the virus, especially if infections after the waning of natural immunity contribute most to evolutionary potential.
Intuitively, our results indicate that unequal vaccine allocation will result in sustained transmission and increased case numbers in regions with low vaccine availability and thus to a higher associated clinical burden compared with a vaccinated population. Under certain scenarios, sustained local transmission could lead to an increased potential for antigenic evolution, which may result in the emergence of variants with novel antigenicity and/or transmissibility and affect epidemiological characteristics globally. Overall, our work underlines the importance of rapid, equitable vaccine deployment and the necessity to export vaccines to regions with low availability in parallel to their becoming available in regions with high access. Coordinated vaccination campaigns across the world, combined with improved surveillance and appropriate nonpharmaceutical interventions to prevent case importation, are imperative.