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A new model looks at how we can get to herd immunity more quickly. Genaro Molina / Los Angeles Times via Getty Images
  • A new data modeling platform finds that prioritizing people at highest risk for COVID-19 isn’t the most effective way to achieve herd immunity when there are limited vaccine supplies.
  • While the vaccine will protect those at highest risk for the disease, it doesn’t stop disease transmission in the community.
  • Experts point out that the model shows the complexity in responding to a pandemic without enough vaccine doses.

With both Moderna and Pfizer-BioNTech’s vaccine candidates approved for emergency use and currently being distributed nationwide, it’s critical that available supplies be used in a way that maximizes herd immunity.

Currently, people at highest risk for COVID-19 are vaccinated first. This includes frontline healthcare workers and older adults.

However, researchers from the NYU Tandon School of Engineering recently developed a novel open-source platform that’s able to create predictive models of COVID-19.

Their data, published in the journal Advanced Theory and Simulations, shows this approach might not be the best way to beat COVID-19.

“We wanted to pursue maximum realism in modeling, toward providing policymakers with the most accurate responses,” study co-author Alessandro Rizzo, PhD, a visiting professor of mechanical and aerospace engineering at NYU Tandon, told Healthline.

“It is in this perspective that we designed and implemented a very detailed model with a spatial resolution at the single building level and a population resolution of the single individual,” he said.

The model Rizzo and team created incorporates detailed elements of virus transmission using a statistically realistic population.

In addition to testing, treatment, and vaccination options, it can even account for the burden of other illnesses with symptoms similar to those of COVID-19.

The modeling platform was developed by a research team led by Maurizio Porfiri, institute professor at NYU Tandon. The platform comprises a model of COVID-19 for the entire town of New Rochelle in Westchester County, New York.

The model replicated New Rochelle’s structure, geographically and demographically, using information from U.S. Census statistics, and superimposed a high-resolution representation of the pandemic at the individual level.

The model also considered physical locations and unique features of people in the community, like behavioral trends or local mobility patterns.

Rizzo said vaccinating older adults first is effective to reduce deaths, since older people have a higher death rate from COVID-19.

However, prioritizing people with a high risk for COVID-19 had only a marginal effect on the number of COVID-19 deaths.

“Our findings are not extremely surprising if put in the framework of scarce resource allocation,” Rizzo said. “They provide a more nuanced point of view than the mainstream narrative about prioritization in vaccination.”

“When you look at who is dying from this disease, by far away, it is those older than age 60 and with higher-risk conditions. This accounts for more than 75 percent of the deaths and most hospitalizations,” said Carl Fichtenbaum, MD, a professor of clinical medicine at the University of Cincinnati College of Medicine. “So, vaccinate those at risk, and they will be protected, lowering the numbers of people being hospitalized or dying.”

But according to Rizzo, his team’s model found that with a limited vaccine supply, that policy may not be the most effective one at stopping the new coronavirus.

Instead, prioritizing people who may be most at risk for transmitting the virus, and not at risk of dying from the disease, may be most effective at curbing COVID-19 transmission.

“With a small number of available doses of vaccine, the effect on the overall transmission through the population depends only marginally on the prioritization strategy,” Rizzo said. “We don’t envisage a clear advantage on the global number of infected and deceased people if we prioritize sanitary personnel or first responders.”

Rizzo emphasized that vaccine prioritization is useful to protect certain people, like teachers (to keep schools open) and doctors (to treat the sick).

Nevertheless, he said that these kinds of decisions “have to be taken by policymakers with the support of models like ours.”

Miriam Smith, MD, infectious disease physician at Long Island Jewish Medical Center in Queens, New York City, said experience with other viruses suggests that more than two-thirds of the population would need to achieve herd immunity to significantly reduce spread of the new coronavirus.

She also cautioned that how long protective immunity will last, either from contracting an infection or getting vaccinated, is still unknown.

“Herd immunity is the resistance to infection that a population can develop as a result of vaccination or previous infection,” Smith said. “A substantial portion of the population needs to be vaccinated to safely achieve herd immunity against COVID-19 to decrease the amount of virus that can be spread.”

She maintained that physical distancing, mask use, and hand hygiene are effective in slowing the spread of COVID-19.

Smith said these recommendations will remain in place as “more data are collected regarding duration of immunity, availability of other viral vaccines that are currently in development, the timing of additional boosters, and so on.”

Rizzo said the new model also pinpointed the benefits of lockdowns to stop disease transmission.

He explained that his study was tailored around situations when people’s mobility was reduced due to lockdowns, when some people were already physically distancing.

“That is, when some countermeasures have already been put forward and people are aware of the dangers of having normal social interactions,” he said.

Rizzo and team preferred to adopt this scenario to provide policymakers answers that mostly reflect the current situation.

“These [lockdown] measures are 75 to 80 percent effective when used correctly,” Fichtenbaum confirmed.

He added that if people physically distance, wash their hands, and wear a mask, it helps to control disease transmission.

“We are envisaging scenarios where mobility is gradually restored. Hence, we are incorporating relevant modeling elements in the next releases of our model,” Rizzo said.

A new data modeling platform finds that prioritizing people at highest risk for COVID-19, such as first responders or older adults, isn’t the most effective way to achieve herd immunity when there are limited vaccine supplies.

Experts say that a substantial portion of the population must be vaccinated to safely achieve herd immunity against COVID-19 and decrease disease transmission.