LULU GARCIA-NAVARRO, HOST:
Now to the pandemic. As the new vaccines against the coronavirus are rolled out, health officials still face a problem. Who gets immunized first? Even if the Biden administration releases all available doses, for a while, at least, supplies will be limited. NPR's Joe Palca says mathematicians can help determine how best to dole out those shots.
JOE PALCA, BYLINE: It's common sense to say that if you have a vaccine for COVID-19 and it works well, you should use it first to protect people who are most vulnerable to dying from the disease.
DANIEL LARREMORE: But it's also common sense to say, well, we should take this great vaccine and use it to break down the processes of transmission by vaccinating the people who are most responsible for the spread, thereby protecting everyone.
PALCA: That's Daniel Larremore, a computer scientist at the University of Colorado BioFrontiers Institute. The people most likely to spread the COVID-19 virus tend to be young and healthy. People most likely to die from it are mostly older and more frail.
LARREMORE: Any time common sense points us in two opposite directions, that's where mathematical models can help us try to differentiate between one commonsense solution and another and when you might choose one versus the other.
PALCA: Larremore makes these models. Tell the model things like how effective the vaccine is at preventing disease or how much virus is circulating in a community and, critically, how fast the vaccine is being rolled out, and the models will tell you where you can have the most bang for the buck, as it were. Larremore says if vaccines were widely available, the models say it makes the most sense to give them to people likely to spread the disease.
LARREMORE: However, if the vaccine is rolled out slowly, which is currently the case, and if community transmission is high, which is also currently the case, then it becomes better to prioritize adults over 60 to minimize mortality.
PALCA: That's close to what the Centers for Disease Control and Prevention is currently recommending, although the CDC guidelines also call for vaccinating people likely to be exposed to the virus, such as frontline health care workers. But even if a mathematical model suggests the most effective path, it doesn't provide all the answers public health officials need.
Mark Jit is at the London School of Hygiene and Tropical Medicine.
MARK JIT: You still have to make some difficult value decisions like, you know, how many lives in older people are you going to save, how many lives in younger people, how many lives in different people, richer, poorer people. So there are some really tricky value decisions, but those are inherent in the fact that we have limited supplies of the vaccine. So we have to make hard decisions about who to give it to first.
PALCA: Right now, modelers are trying to help public health officials decide if it makes sense to use a single dose of the Moderna and Pfizer vaccines to extend the limited supply, even though the vaccine has only really been tested using a two-dose regimen.
Laura Matrajt of the Fred Hutchinson Cancer Research Center has a model that allows her to test various what-if scenarios. Here's one scenario.
LAURA MATRAJT: If the first dose is highly efficacious and we have stringent social distancing interventions in place, then vaccinating with a single dose is optimal.
PALCA: The need for stringent social distancing is because while it's clear the vaccine prevents disease, it's not so clear it totally prevents someone from transmitting the COVID virus. And Matrajt emphasizes that the single-dose strategy only works if a single dose is efficacious.
MATRAJT: We should do whatever it takes to know what the efficacy of a single dose is.
PALCA: Matrajt also says her model and others say it's important to get people vaccinated as quickly as possible.
MATRAJT: If you don't roll the vaccine fast enough, the effect of the vaccine will be very, very limited.
PALCA: And like many of us, Matrajt has a personal reason to want the vaccine soon.
MATRAJT: And if they roll the vaccine in six months or seven months, that means that I'm going to be stuck in my house for another seven months.
PALCA: Mathematical modelers are people, too, you know?
Joe Palca, NPR News.
(SOUNDBITE OF JING CHI'S "STAN KEY") Transcript provided by NPR, Copyright NPR.