Should Coloradans Who've Had Coronavirus Get The Vaccine Last?

New research shows that, in some cases, people who've had COVID-19 should give up their spot in the vaccine line to someone who hasn't been infected.

University of Colorado Boulder researchers worked with the Harvard T.H. Chan School of Public Health and the University of Chicago to conduct the study, which used mathematical modeling to determine how different distribution strategies could play out in cities around the globe.

“Our research suggests that prioritizing people who have not yet had COVID could allow hard-hit communities to stretch those first doses farther and get to some of the herd immunity effects sooner,” said Dan Larremore, a computational biologist at CU Boulder's BioFrontiers Institute.

He and lead author Kate Bubar, a graduate student in the university's Department of Applied Mathematics, teamed up with their Harvard and Chicago colleagues to run the modeling, which showed that, in general, if saving lives is the objective, enabling people 60 and older to go to the front of the line works best. If reducing future infections is the goal, however, the 20- to 49-year-old crowd should get the first doses. In very few cases did vaccinating children first make sense.

Results from the United States, Belgium, Brazil, China, India, Poland, South Africa and Spain are included in the paper.

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The researchers modeled what would happen in five different scenarios in which a different group got to be first in line: Children and teenagers, adults between the ages of 20 and 49, adults aged 20 or older or adults aged 60 or older. In the fifth scenario, there was no distribution strategy and anyone who wanted a vaccine got one while supplies lasted. Different strategies worked better or worse, depending on each area’s population, but a few findings jumped out.

“In the broadest array of scenarios, across countries, prioritizing adults 60-plus first was the best way to minimize mortality,” Larremore said.

“If we want to go back to pre-pandemic behavior, giving the first wave of vaccines after healthcare workers to older adults is the way to go.”

That finding has already been used by global health experts to inform vaccine distribution strategies, with the World Health Organization the Centers for Disease Control referencing the study in recommendations to prioritize older adults.

Colorado is preparing to distribute the COVID-19 vaccine in three phases over the next nine months:

While the CU Boulder joint study looked at the broadest array of scenarios, which shows prioritizing adults 60-plus first was the best way, it also looked at other important variables. As individual states determine who’s next, the story gets more complicated.

“If transmission is rampant, and hospitals are being overwhelmed, then directly protecting those who are at the highest risk for severe outcomes is the best way to save lives and decrease the stress on our healthcare system,” Bubar said.

“But, if instead, transmission is relatively low in a given area then prioritizing those who have the most contacts would be better— provided that the vaccine blocks transmission.”

In communities where COVID-19 had already infected large portions of the population, prioritizing those who haven't tested positive for the virus could allow health agencies to stretch the vaccine farther and save more lives.

For example, in New York City, where 27 percent of people have already been infected, vaccinating one in five people over age 60 could bring mortality down by 73 percent, the research shows.

“But the city could get that same level of population protection by vaccinating just one in six older adults — if those without antibodies were brought to the front of the line,” Larremore said.

So just how might a city go about identifying people who’d already been infected? In cases where vaccine availability was scarce, it might be worth having people take an antibody test before getting the vaccine, the report's authors said. Alternatively, people who already been infected with COVID-19 could just be asked to consider sparing their dose for someone who does not already have partial protection from the virus.

In a city like Boulder, however, where only a small percentage of people have already been exposed, testing people prior to vaccination might not yield enough benefit to be worth the effort, the researchers said.

“We hope that state governments will consider the local status of the epidemic in their decisions about who to prioritize,” Bubar said.

The research is under peer review, and the authors hope to publish in early 2021. In the meantime, as vaccines become available and policymakers begin to make tough decisions influenced by emotions, ethics and the economy, the authors hope their work can provide some statistical footing.

“We need policy decisions that are well-anchored in the most rigorous scientific estimates,” Larremore said.

“This paper is all about providing them.”