With novel data modeling, Tandon team predict effects of waning vaccine immunity against COVID-19

a textured city map with a syringe

To date, approximately 42.6% of the world and 63.8% of the U.S. have taken at least one dose of a vaccine for the virus that causes COVID-19, while 30.8% and 54.5%, respectively, are fully vaccinated. 

There is growing indication that the immunity provided by these vaccines wanes over time; and that third-dose booster shots would restore the original protection and enhance people’s immunity against the most recent variants, including the Delta variant. As many countries, including the U.S., launch revaccination campaigns, insight into the short-term roll-out of booster shots is needed. 

A team from NYU Tandon including Maurizio Porfiri, Institute Professor at NYU Tandon,  Agnieszka Truszkowska, a postdoctoral researcher, Zhong-Ping Jiang, professor of electrical and computer engineering, and Alessandro Rizzo, visiting professor of mechanical and aerospace engineering, with national and international collaborators (Sachit Butail of Northern Illinois University, Emanuele Caroppo of Azienda Sanitaria Locale Roma 2, and Lorenzo Zino at the University of Groningen) are developing a systematic study of the effectiveness of a re-vaccination campaign in the upcoming 2021–2022 fall/winter season, considering as key factors the rate of administration of booster shots, the spread of the Delta variant, and the population coverage of testing policies implemented during this phase. 

Results of their study indicate the need to quickly begin the vaccination campaign and keep vaccinating at a fast speed to combat the effects of waning immunity and perform robust testing programs. In fact, the team found that low testing efficacy may lead to a disastrous increase in both infections and deaths, irrespective of vaccination efforts of any intensity.

“We explore two parameter ranges,” said Porfiri. “One is the rate at which you administer the booster shot to people, and the other is the rate at which you test and trace.” He explained that the research also takes into account that a large number of people choose not to be vaccinated. “So you have this fine balance, you have this interplay, between resistance of the population, and the need to revaccinate the people that have lost their immunity from the first vaccines.”

The researchers employed a high-resolution agent-based model (ABM), which faithfully provides a one-to-one digital reproduction of a real, medium-sized U.S. town. As a test case, they simulated COVID-19 spreading in the town of New Rochelle, NY — a line of inquiry-based on previous work by the researchers modeling the initial spread of COVID-19, and the effects of reopening during the initial wave of vaccinations. Those findings cast doubt on the virtues of prioritizing vaccination of high-risk individuals as a way to lower deaths from COVID-19, and that significant improvements could only be obtained by vaccinating a large fraction of the town population.

The new model goes a step further, taking into account the predominant Delta variant, booster shot campaigns, and co-existence of three vaccines (Johnson&Johnson, Pfizer, and Moderna), providing different levels of protection over time.

“The mechanism we used is identical to that of the first study,” said Rizzo, “We assume that the number of people that live in New Rochelle hasn't changed dramatically, that people work and go to school at the same places, and so on. The structures of the city, and movements of the citizens — whatever is related to census, mobility and activity — remains the same. But we changed the clinical parameters taking into account variables like the spread of the Delta variant, the employment of contact tracing, waning vaccine immunity, and the availability of booster shots.”

The study suggests that a booster shot campaign should be performed at a fast pace, involving at least one percent of the population per day (the double of the peak vaccination rate during spring 2021), to have effect on curbing the count of cases and casualties. At the same time, highly-effective testing and tracing campaigns should be carried out. Indeed, the combination of the current vaccination rate (below 0.5%) and a low-efficacy testing campaign would lead to a case and death toll comparable with those experienced during the first wave. 

While the researchers ultimately agree that a booster campaign would be beneficial, the benefits pale in comparison to proper testing, contact tracing and quarantining when appropriate.

Research by Maurizio Porfiri et al finds stark differences in the number of COVID-19 infections between a) a hypothetical circumstance in which at least one percent of the population per day receives vaccine boosters (green line), and b) the actual vaccination rate in September 2021, in New Rochelle, NY (red line).