"Both ethical and mathematical models have to face real-world practicalities."
The whole world wants a vaccine, but countries will naturally try to secure a supply for themselves first. The original grid relied on diaries. Today, our ability to gather data through real-time cell-phone and online activity may be even greater.
When social distancing became widespread this past spring, it dramatically altered the input into the typical transmission model, says Springborn. Data from the Institute for Health Metrics and Evaluation at the University of Washington shows the power of social distancing in reducing transmission. The contact grids in previous studies are “from pre-pandemic times,” Springborn wrote in an email. “We know that contact rates are very different under social distancing and we want to account for that. And we expect social distancing to soften as the number of infections falls. Human nature: As risk falls, so does risk-mitigating behavior.”
That needs to be modeled as well. And it will influence the expectations for a vaccine’s rollout and success. In fact, Lee maintains, if we had 90-percent compliance with face masks and social distancing right now, we could contain the virus without a vaccine.
In the study by Springborn, Buckner, and Chowell, social distancing is modeled by creating age-stratified categories for both essential and nonessential workers. Essential workers—health-care workers, grocery workers, and many school teachers, among others—are at high risk for infection because they cannot socially distance. This model finds that deaths, as well as total years of life lost, are dramatically decreased when essential workers are prioritized to receive the vaccine. Older essential workers between 40 and 59 should be prioritized first if the goal is to minimize deaths, the authors maintain.
With no vaccine, about 179,000 people may die in the first six months of 2021, Springborn says. His team’s model suggests that deaths could decline to about 88,000 if a vaccine were introduced gradually, given to 10 percent of the population each month, and distributed uniformly without prioritizing any groups. But distributing vaccines in a targeted way, based on people’s ages and whether they are essential workers, could save another 7,000 to 37,000 lives, depending on the situation.
There are other methods of teasing out social connectivity beyond diaries and cell-phone data. Census and other data reflect age, profession, and socioeconomic status, and Lee includes this information in her models. “The zip code gives you a huge amount of information,” she says. Public health data on disease prevalence and hospitalizations can tease out the other unrelated diseases that COVID-19 patients have, as well as vulnerabilities in a given area. Even information on a city’s housing, whether skyscrapers or single-family homes, can give a clue to how closely people are packed together and how likely they are to interact. Inputting this kind of data allows for a vaccine rollout that is sensitive to local conditions. Lee would need to model about 500 representative cities around the US, she says, to cover the country accurately.
As powerful as the models can be, they are an imperfect guide. Inevitably they intersect with deep and broad social concerns. The pandemic has disproportionately harmed and killed minorities and those with lower incomes. For that reason, various groups are looking into the ethical principles that should frame vaccine allocation, according to Hanna Nohynek, deputy head of the Infectious Diseases Control and Vaccinations Unit at the Finnish Institute for Health and Welfare, and a member of the WHO’s SAGE Working Group on covid-19 vaccines.
In the US, the National Academies of Sciences, Engineering, and Medicine has begun to model an equitable allocation of a vaccine. In addition, two other important models have emerged, one associated with University of Pennsylvania School of Medicine and the other with Johns Hopkins University. Both are guided by concerns about ethics, fairness, maximizing benefits, building trust, and the greater public good.
But building trust can be challenging in practice. For instance, it’s widely acknowledged that Black people have experienced hospitalization and death at disproportionately higher rates than white people. Yet when ethicists begin to talk about prioritizing Black people for vaccines, it can be perceived as an intent to experiment on them by pushing them to the head of the line. If there is concern among African-Americans, it’s a logical reaction to “a vast history of centuries of abuse of African-Americans in the medical sphere,” says medical ethicist Harriet Washington, author of Medical Apartheid.
Ultimately, both ethical and mathematical models have to face real-world practicalities. “It’s hard because math essentially boils down to a utilitarian calculus,” says Lipsitch, the Harvard epidemiologist.
Nonetheless, says Larremore, the models will help guide us in the uncertain early days. “Vaccines take a while to roll out,” he says. "We can’t let our foot off the gas the moment a vaccine is announced.”