Behind the paper: Japanese Contact Patterns during the COVID-19 Pandemic

In this post, we talk to the authors of the recently published paper, Continuing to be cautious: Japanese Contact Patterns during the COVID-19 Pandemic and their Association with Public Health Recommendations. These responses were written by Tomoka Nakamura on behalf of Ryo Kinoshita, Akira Endo, Katherine E. Atkins, Hitoshi Oshitani, Yoko Ibuka, Motoi Suzuki, Koya Ariyoshi, and Kathleen M. O’Reilly.

What led you to decide on this research question?

I started my research during my PhD at the London School of Hygiene and Tropical Medicine (LSHTM) and Nagasaki University. The initial plan for my PhD was to focus on the cost-effectiveness of the rotavirus vaccine in Japan. However, I started my PhD right in the middle of the pandemic in 2020, and since I had spent time living in Europe and Japan, I experienced first-hand the vast differences in governmental policies and human behavior.

For instance, there were strict lockdowns in the UK that restricted movement and social gatherings. In Japan, on the other hand, there was strict border control that restricted many from entering the country from overseas, but it did not implement any lockdowns, mask and vaccine mandates. This made me curious as to why we continued to see differences in COVID-19 incidence and deaths in Japan and the UK.

An empty street in Kyoto city where it is normally bustling with tourists (2021). (Photo credit: Luca Malatesta)

Additionally, I was exposed to the social contact surveys called CoMix that were being implemented in the UK by my colleagues at LSHTM. Understanding the changes in contact patterns in the UK led me to question if there were similar changes that influenced COVID-19 transmission dynamics in Japan.

Could you talk us through how you designed your study? What was important for your team as you created the study team?

In 2020, we started by looking for baseline contact data in Japan as we searched for social contact surveys done before COVID-19. Understanding pre-pandemic patterns was key to measuring how behaviors changed during the pandemic. Our team carefully designed the contact surveys, drawing on global studies for guidance, while also balancing the research questions we wanted to answer against the need to avoid survey fatigue for participants.

The design of the first two surveys was a race against the clock. We aimed to conduct the first survey while the emergency declaration was still in effect in Japan, and the second survey shortly after it was lifted. Back in 2020-2021, we did not know when the pandemic would end or what additional public health policies might be introduced, so we wanted to make the most of the opportunity to capture changes in behavior.

Our study team included experienced epidemiologists, mathematical modelers, clinicians, policymakers, and a health economist. Many of us were learning about COVID-19 as it unfolded, so it was important to approach the study without preconceptions about contact patterns in Japan. I was part of a small team at Nagasaki University developing a mathematical model of COVID-19, and we also paid attention to how the public was informed about reducing contacts, for example, through posters around the city (photo below). Seeing these outreach efforts gave our team a broader perspective on the potential impact of our research and how it could support public health efforts in communities.

Poster shown in front of a public library in Nagasaki city titled “Please Refrain from Contacting with Others during the Golden Week National Holidays” (May 2021). It showed a simplified version of our mathematical model outputs, so the public can visually understand how reduction in contacts can flatten the curve (Photo credit: Toshihiko Sunahara)

What challenges did you encounter during your study?

One of the challenges was finding a suitable baseline for comparison. Contact survey data in Japan before COVID-19 were limited, so we had to carefully determine what could serve as a meaningful benchmark against which to measure pandemic-era changes. Formulating the contact survey questions in Japanese was tricky as some questions needed to be worded differently than in English to ensure clarity and comprehension.

Another challenge was the constantly shifting context. During the pandemic, we were all trying to make sense of the disease while new variants emerged, public health measures were introduced or lifted, and new vaccines became available. These overlapping and rapidly changing factors made it difficult to disentangle what was driving changes in contact behavior.

On top of that, many epidemiologists and medical professionals were supporting outbreak response by working with national and local governments. It was difficult to reach experts for their feedback on our research. Almost all communication among our study team was via email or online meetings. Even when we were in the same country, face-to-face meetings were impossible due to COVID-19 restrictions.  

What did you find most striking about your results? How will this research be used?

One of the unexpected results from our study was that the frequency and duration of contacts in Japan did not immediately increase after COVID-19 governmental policies lifted. Even three years after the start of the pandemic, contacts only gradually increased but with caution as the majority of the survey participants continued to wear masks and received their third dose of the COVID-19 vaccine. As expected, school-aged children and healthcare workers reported higher contacts than a company employee, but government employees were among those that had higher contacts in our study. These individuals may have included public school teachers and prefectural and city office employees who regularly interacted with others. This was a reminder that depending on the country context and type of occupation, one can be exposed to having higher contacts.

People exercising in the morning while physically distancing from one another at a park in Tokyo, Japan (2021). (Photo credit: Kathleen O’Reilly)

During the beginning of the study, the preliminary results were shared with the COVID-19 advisory board headed by the Ministry of Health, Labor, and Welfare. This allowed the experts to understand contact patterns of different ages and whether there were any immediate changes in contacts with the implementation of governmental recommendations.

Although the pandemic has ended, our study results can be used to better understand the factors that influence contact patterns in preparation for future public health emergencies. Age-specific contact data are often used to develop mathematical models that project the spread of infectious diseases. By recognizing how contact patterns vary widely by age and country, our contact survey data can be used to tailor mathematical models that better describe disease transmission. We hope this, in turn, will support the implementation of public health policies that target the specific needs of each country.

What further research questions need to be addressed in this area?

There are still many questions about social contact patterns in Japan and globally today. Have people returned to pre-pandemic behaviors, or are some cautious habits, like wearing masks in crowded places or staying home when experiencing respiratory symptoms, continuing? Conducting another contact survey could help us understand current patterns and how they differ from both pre-pandemic and pandemic times.

Understanding these changes is important because shifts in social behavior can influence how infectious diseases spread and how effectively they can be mitigated. Continued research in this area can help guide public health policies and preparedness for future outbreaks.

Why did you choose PLOS Global Public Health as a venue for your article?

We chose PLOS Global Public Health because it was open access and covered a wide range of global health issues, attracting a broad scientific audience. Although our study is quantitative, it also has a socio-behavioral dimension as contact patterns are shaped by individual decisions and cultural norms. We felt it was important to share our findings in a journal that values cross-disciplinary perspectives and accessibility.

Finding the right journal was not straightforward. By the time we implemented our final contact survey in 2023, global attention had already shifted from the pandemic, even though Japan was experiencing its highest number of confirmed COVID-19 cases. For many journals, COVID-19 was no longer seen as front-page science, and it became increasingly difficult to identify suitable outlets and reviewers. This made us appreciate the role of journals like PLOS Global Public Health. While timeliness in disseminating results is crucial, we also hope more journals will continue to highlight research that remains relevant even after a public health emergency has formally ended.