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Over the next few months, the Biden administration will offer all fully vaccinated Americans a COVID-19 booster shot — assuming it can get approval, based on limited data, from the Food and Drug Administration and the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices. Meanwhile, about 47 percent of Americansand over 70 percent of people around the world — are still not fully vaccinated. Can the United States boost the already vaccinated while vaccinating the unvaccinated?

In June, President Biden announced that the United States would donate 200 million Pfizer vaccines to low-income countries in 2021 and 300 million in 2022 — about 10 percent of Pfizer’s anticipated production. Vaccinating the world obviously helps other countries. It also protects Americans from new more infectious or deadly variants and shores up global supply chains for food, equipment, and other products Americans need.

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Vaccinating the unvaccinated is the most effective way to save lives. By the end of June, the 270 million vaccine doses the United States administered saved an estimated 279,000 American lives and averted 1.25 million hospitalizations. This translates into roughly 100,000 lives saved per 100 million doses.

Third shots for the vaccinated public will have far less impact, especially beyond the small immunocompromised population and, potentially, elderly populations. Centers for Disease Control and Prevention data suggest the Pfizer and Moderna vaccines remain over 90 percent effective against hospitalization. The recommendation for boosters is based on the belief that providing boosters will reduce asymptomatic and mild COVID cases from the Delta variant. Although boosters have not been proven to prevent breakthrough infections in randomized controlled trials, reducing breakthrough cases is a worthy goal — but far less important than preventing death and hospitalization. Worldwide, about 10,000 people are dying every day of COVID-19, almost all unvaccinated. This is not just a distribution problem, but a supply problem: Even in Thailand, an upper-middle-income country of 32 million people with a strong health system, just 11 percent have been fully vaccinated.

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The White House claims boosting already vaccinated Americans will not impede global vaccination. Instead, they say “we can do both”: vaccinate Americans and lead in vaccinating the world. So far, the United States leads the world in vaccine donations, with 110 million delivered. But the fundamental question is whether we will do both. Can we administer an additional 176 million doses to reduce COVID-19 infections among US adults and adolescents who are well-protected from severe disease without impairing — and even while strengthening — the flow of life-saving doses for the unvaccinated worldwide? And what if other countries follow suit with boosters, further drawing on global supply?

Decisive and creative action is needed to diminish — perhaps even eliminate — trade-offs between third doses for Americans and increasing global vaccination. Without this action, “we can do both” will remain an aspiration rather than reality, and both Americans and the world will suffer needlessly.

The most powerful — but most challenging — way of reducing trade-offs is to increase the number of vaccines produced. Boosters could send a signal for greater demand — though so could funding COVAX, a global vaccine program, to purchase doses. Research suggests that boosting manufacturing production is best done by helping companies expand their capacity. Unfortunately, building capacity to produce mRNA vaccines is an uncertain multi-month solution that faces myriad bottlenecks, from bioreactor bags to lipid nanoparticles that envelop the mRNA and facilitate cellular uptake of the mRNA to make spike protein to stimulate the immune system to fight the coronavirus. While necessary, increasing physical supply must be part of a larger strategy to vaccinate the world.

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Using supply more efficiently is a quicker way to mitigate trade-offs. The United States has a moral obligation to reduce the number of doses the boosters require from the pool of available vaccines. This can be done by “fractional dosing”— finding the minimum mRNA quantity that produces a protective antibody response. For example, we know a half-dose of the Moderna mRNA vaccine generates nearly the same antibody response as a full dose in the unvaccinated. Yet the National Institutes of Health and other agencies have failed to complete dose-finding studies even though we’ve been administering vaccines for over eight months. In fact, the FDA is reportedly resistant to a half-dose booster from Moderna, despite the obvious global benefits from doubling effective Moderna booster supply. Such trials are urgently needed, and could be completed in a few weeks because they merely require measuring antibody production following a booster — the same biological (as opposed to real-world) outcome that is currently used to justify boosters. If fractional dosing for boosters is successful, it could be a major step toward fulfilling Biden’s promise of “doing both.” And, as a bonus, it might diminish vaccine side effects.

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“Mix-and-match” vaccination could also better steward global supply. Studies suggest a viral-vector vaccine, such as Johnson & Johnson’s, after two mRNA doses might boost antibodies as much as — or more than — a third mRNA shot, perhaps by activating different immune pathways. Mixing and matching could allow mRNA vaccines to protect the unvaccinated globally while protecting American booster recipients just as well or even better. Again, the NIH has not conducted the appropriate studies but needs to initiate them as soon as possible.

Yet another strategy for “doing both” is to use global supply more slowly — diverting a stream to boosters instead of a flood. Currently, third doses are proposed eight months after the second, but officials admit this is a “judgment call” based on antibody levels rather than medical outcomes. The White House says boosting now will require 100 million doses in 2021; boosting at one year instead and donating those same doses could potentially save over 100,000 people worldwide, as the vaccine supply continues to increase. Even merely postponing third doses beyond eight months in lower-risk populations could save tens of thousands of lives in the rest of the world, especially if it helps induce other countries to also adopt more targeted booster policies as well.

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Finally, boosters must prompt greater efforts to reduce waste. More than 50 million vaccines sit idle in American freezers and more than 15 million doses have been wasted since March, often due to mismanagement or want of demand. For instance, the state of Georgia alone has destroyed more than 600,000 vaccines, with nearly a million more at risk. Instead of tolerating a policy that “unused expired vaccine is a normal part” of large-scale vaccination, the CDC and other organizations should recognize that we are not in a “normal” situation but a pandemic, and ensure that potentially expiring vaccines are used as boosters.

While boosters in American arms may prevent infections, they will save few lives, because two shots reduce serious illness by 90 percent or more. If instead deployed to global hotspots, these same vaccines could save 100,000 lives. The United States has a global moral responsibility to ensure its booster campaign does not deprive people abroad of life-saving vaccines. It is in the national interest to protect Americans from continued economic disruption and more harmful variants from uncontrolled spread worldwide. Decisive action to increase and optimally use vaccine supply is needed to protect the world and the United States from the continuing harms of the pandemic.

Govind Persad is assistant professor at the University of Denver Sturm College of Law. Dr. William Fiske Parker is assistant professor of pulmonary and critical care medicine and assistant director of the MacLean Center for Clinical Medical Ethics at the University of Chicago. Dr. Ezekiel J. Emanuel is vice provost for Global Initiatives and codirector of the Healthcare Transformation Institute Perelman School of Medicine and the Wharton School at the University of Pennsylvania.