Modeling Covid-19 vaccination efforts in the U.S.

A syringe in vaccination vial lying flat on a table with another vaccination vial beside it.
Vaccine vials and syringe. (Credit: iStock)

Two new papers coauthored by UF mathematician Burton Singer explore the role of vaccination in curbing the spread of COVID-19 within the US. Singer is a professor in UF’s College of Liberal Arts and Sciences, and he is also a faculty member with the Emerging Pathogens Institute. He focuses on modeling infectious disease dynamics.

In the first paper, published in EClinical Medicine by The Lancet, Singer and his coauthors evaluated the effect of an expedited vaccine campaign upon lessening the anticipated spread of COVID-19 due to newly emergent and more transmissible variants.

They modeled the spread of the original strain of SARS-CoV-2, as well as the B.1.1.7 variant which is hypothesized to be 40% to 80% more transmissible and 35% more lethal. In the model, the researchers compared accelerated vaccination schedules of 1.5, 2, 2.5 and 3 million doses administered daily to the current rate of roughly 1 million doses daily.

The model estimates that at the current rate, the B.1.1.7 variant could dominate the US within two to 9 weeks. But tripling the vaccination schedule to 3 million doses per day would avert about 152,000 hospitalizations and almost 48,500 deaths over 300 days.

The findings show that our country’s current pace of vaccination is likely too slow to prevent a possible surge in COVID-19 hospitalizations and deaths due to the B.1.1.7 variant.

“A bigger and unaddressed problem is the duration of protection of the vaccines being distributed,” Singer says. “If protection lasts for only one year, for example, then we already need to be producing a new vaccine for a new round of vaccinations starting in 2022. If protection lasts 18 months, then there is a more delayed schedule, but we need to start thinking about this.”

In the second paper, published recently in Clinical Infectious Diseases, Singer and his coauthors built a model to estimate the effect of a concerted COVID-19 vaccination campaign upon new infections. The researchers assumed that up to 70% of any given age group could be vaccinated, and they focused on modeling people aged 18 years old and older. The model assumes a vaccine that mirrors those on offer in the US: a two-dose vaccine schedule, 21 days apart, with 95% efficacy. They also assumed that up to 40% of the adult population would receive a vaccine within about 9.5 months.

Their model estimated that the virus’s attack rate would be cut in half if all these conditions were met. (The attack rate is the proportion of people falling ill divided by the whole population in a given time period.)

“But in hindsight, we may have put in more optimistic scenarios than are true to reality,” Singer says. “We have at least 30% of the US population that is hostile to vaccination, and with this volume of refusals we won’t get close to protection for the population as a whole.”

In other words, while the model indicates what a possible future could look like with greater acceptance of the vaccine by wider margins of the US public, our lived reality may differ. While individuals will receive the benefits of vaccination, population-level “herd immunity” likely won’t be reached in the US via a robust vaccination effort due to the pre-existing strength of the anti-vaccination movement.

Written by: DeLene Beeland