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Hawaiʻi Gov. David Ige allowed individual counties to make their own COVID-19 pandemic rules and orders beginning on December 1, 2021. That was an appropriate decision and an example for government responses to future pandemics, according to a computational analysis by researchers at the University of Hawaiʻi at Mānoa.

Department of Mathematics experts, led by Professor Monique Chyba, also a member of the Hawaiʻi Pandemic Applied Modeling Work Group, conducted a study of COVID-19 case counts and the coronavirus’ spread across Hawaiʻi counties from the beginning of the pandemic in March 2020 through January 2021. Researchers wanted to figure out how a pandemic spreads throughout an island chain, something that is absent from current literature. Among the major findings, viral spread within counties occurred at different times and causes for the fluctuations in case counts differed county by county.

“Our work highlights the need for localized measures and possibly targeted mitigation measures at the county level and as opposed to the state level for the most effective pandemic control,” according to the study.

COVID-19 spread in Hawaiʻi

The COVID-19 spread between counties (Honolulu, Maui, Hawaiʻi and Kauaʻi) aligned until the start of the Safe Travels program on October 15, 2020. According to the researchers, ​​Hawaiʻi County showed an increase in cases right before the Safe Travels program was launched, which was attributed to a pair of clusters (one in Hilo and one in Ocean View). Maui County also had a few clusters, including one around October 20, 2020, on Lānaʻi and another major one in early January 2021, in Kahului. After Safe Travels was launched, both Honolulu and Hawaiʻi counties showed a slight increase in contrast with Maui County that displayed a very sharp increase.

“The reason is that changes occurred more rapidly in the neighbor islands, for instance the peak for Honolulu County is based on a build-up starting in June 2020, while for Hawaiʻi County the peaks are much narrower,” according to the study.

In addition, researchers did not find a correlation, and in some cases, an anti-correlation between mobility and movement around the counties with rises in case counts.

“It suggests that the spread of the virus among households, especially large and multi-generational, could significantly contribute to the overall daily cases,” the study said.

Hawaiʻi vs. other international islands

Researchers discovered that in 2020, Honolulu County experienced similar waves in case counts compared to Iceland—which detected its first case in February 2020 and had a significant first wave, but then controlled the spread besides a super spreader event triggered by two travelers. In addition, Maui County exhibited similarities with Japan and Hawaiʻi County was similar to Puerto Rico. In a very innovative approach, the paper introduces the concept of merge tree, a topological descriptor of functions, to quantify similarity between the spread in various geographic locations.

The research findings were published on May 18, in peer-reviewed journal, PLOS ONE. The study’s co-authors are Chyba, Associate Professor Yuriy Mileyko, graduate students Prateek Kunwar and Alan Tong, undergraduate student Winnie Lau, and Alice Koniges, Information and Computer Sciences graduate faculty and research investigator in Information Technology Services. This research was funded by a grant from the National Science Foundation.

“​​I’m grateful for this opportunity to inform other people regarding what is happening throughout the islands,” Lau said. “It has been a great experience to learn more about how COVID-19 has impacted Hawaiʻi, along with the importance of modeling and the understanding it provides for different situations.”

Kunwar added, “Working on this project has been a great learning experience for me—not just in terms of the mathematics involved but also in terms of what the goal of modeling a pandemic is—to defeat the model by making informed decisions. It is definitely rewarding to do work which impacts the citizens of Hawaiʻi and in this case, the urgency of events makes it a challenging task as well. My work on this project has translated into reading and exploratory projects on epidemiological models for my students in calculus classes and has led to discussions about correct interpretation of data.”

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This public impact research is an example of UH Mānoa’s goal of Excellence in Research: Advancing the Research and Creative Work Enterprise (PDF), one of four goals identified in the 2015–25 Strategic Plan (PDF), updated in December 2020.

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