Vaccinated? Don’t Let Your Guard Down Just Yet, says Ohio Math Expert

May 12, 2021

Article published in SIAM News shows why social distancing and masking must continue alongside vaccinations if the U.S. wants to see daily COVID cases go down

Cleveland, OH, May 2021 – Daniela Calvetti is fully vaccinated, yet she still carries masks with her at all times and tries to stay at least six feet apart from others – following the Centers for Disease Control and Prevention (CDC) masking guidelines. That’s because Calvetti, a math professor at Case Western Reserve University in Cleveland and longtime member of Society for Industrial and Applied Mathematics (SIAM), spends much of her time charting a first-of-its-kind math model she created to predict coronavirus spread based in large part on people’s behavior, and she says the findings are sending a clear message – both of hope and warning.

In an article published in SIAM News, Calvetti explains how her team tackled the problem of modeling COVID-19 spread by accounting for complex nuances such as the presence of asymptomatic spreaders and the effect of vaccines. The model – which is currently used by the university’s Center for Community Health Integration to accurately predict COVID-19 case counts in 31 Ohio counties – shows that the U.S. won’t see a significant and stable decrease in cases until closer to 70 percent of the population receives their first dose of vaccine, and that mask wearing and social distancing measures are needed in the meantime to contain the spread.

“The most eye-opening finding for me is how quickly this virus can move from one place to another due to the hidden virus spreaders, those people who carry the virus without showing symptoms,” said Calvetti, whose model shows that if restrictions are lessened too soon, daily case counts will rise – even double from where they are today – despite the fact that more people are getting their vaccines.

“Our model predicts that for every two infected people we know about with symptoms, there’s one out there without any, and that’s scary,” she said. “I may not get sick from the disease, but there is still a lot to be learned about transmission by vaccinated individuals and until there is clear scientific evidence that I am not an asymptomatic carrier – even now that I’m fully vaccinated – I will do my part and mask up!”

That is because, as the CDC reports, although the vaccine is proven to be effective at keeping us from getting COVID-19, they are still learning how well vaccines prevent people from spreading the virus that causes COVID-19 to others, even if you do not have symptoms.

Calvetti’s model shows that there are reasons why the daily cases have plateaued at roughly 50,000 even though more than 40 percent of Americans have received at least one vaccine dose. She said the reason for this is most likely due to the new variant – which is shown to be 60-70 percent more contagious than the original variant – and the fact that people have been socializing more since vaccinations started.

“Some people thought they would see cases go down as vaccinations go up, and because that hasn’t happened, they think it’s a sign that vaccines aren’t working. That’s simply not the case,” said Calvetti, cautioning that now is not the time for vaccine hesitancy. “The key message – and one that our model proves without doubt – is that without our current rate of vaccination, our cases would be much, much higher and that’s why we must remain vigilant for the short term.”

The strength of Calvetti’s modeling approach is that it dynamically takes into account both how people change their behavior over time and the virus mutations. For example, when mitigation measures are relaxed, people move about more, whereas when hospital ICUs are full, people adhere better to masking and distancing. These factors are reflected in the number of new cases and translate in dynamic variations of the model parameters.

“We base our model on the belief that the rate of infection depends not only on the behavior of the virus, but also on the behavior of people,” she said.

Over the past year, the team has had a chance to compare their predictions to real world data, and the model has proven to be “more accurate than we dared to hope,” she said. They can also run what-if simulations to show the impact of specific future actions, such as opening restaurants to dine-in service, removing curfews or changing travel restrictions.

Running a simulation to show what would happen in the U.S. if everybody were to stop masking and distancing now, while continuing the vaccination at the current rate, the model shows that daily case counts would more than double, rather than dwindle down to the ideal target of 10,000 by the beginning of July. Based on the findings of her model, Calvetti predicts that, in order for daily COVID cases to significantly decrease, mitigation measures for both vaccinated and non-vaccinated people will continue to be necessary until 70 percent of the population is vaccinated.

“Now is not the time to all take off our masks and get together. Let’s put off large meetings and indoor social activities until we have fewer people in the pipeline, susceptible to infection, and more people vaccinated, and then we can start to relax,” Calvetti said. “The positive note is that assuming vaccine availability continues without disruption and people are willing to be vaccinated, we should be in store for a more normal 4th of July. We just need to be patient a little longer,” she said.


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