The COVID-19 pandemic, declared in March 2020, led to widespread lockdowns globally, drastically altering daily life and habits. Physical distancing measures necessitated increased reliance on digital communication, with mobile instant messaging (MIM) applications experiencing a surge in usage. WhatsApp, the leading MIM application, became a crucial tool for maintaining social connections during this period. This study aims to analyze how communication behavior on WhatsApp changed due to the lockdown and the ongoing pandemic. The research questions are: RQ1: Has WhatsApp communication behavior changed during the COVID-19 lockdown in March/April 2020? RQ2: Are there lasting effects of the pandemic on communication behavior in WhatsApp? Understanding these changes is crucial for behavioral researchers and internet providers. The study uses a large dataset of anonymized WhatsApp chats to examine message frequency, media usage, and daily communication patterns before, during, and after the lockdown, offering insights into human behavior and potential network optimization strategies for future pandemics.

Existing research extensively covers MIM application usage behavior and the impact of COVID-19 on internet traffic. Studies compare WhatsApp communication to SMS, analyzing message frequency, content, and formality. Other research examines group chat dynamics, daily usage, and the role of MIM in coordinating daily life. Regarding the COVID-19 pandemic, studies have documented significant increases in internet traffic, shifts in usage patterns, and the effectiveness of MIM applications in online learning and social support. However, detailed analysis of the impact of the pandemic and lockdown specifically on MIM communication behavior, particularly within WhatsApp, remained limited before this study.

The study utilized WhatsAnalyzer, a tool designed to collect and analyze anonymized WhatsApp chat histories. Users voluntarily submitted their chat data, which was then anonymized, preserving only relevant communication metadata such as message type, length, and timestamps. The data comprised 2577 private WhatsApp chats, containing 25,378,093 messages from 51,973 users. The analysis involved comparing communication patterns in March and April 2020 (lockdown) with the same period in 2019 (pre-pandemic) and comparing the entire year from March 2020 to February 2021 (pandemic year) with March 2019 to February 2020 (pre-pandemic year). Statistical tests, including Chi-square tests, paired t-tests, and Kolmogorov-Smirnov tests were used to assess the significance of observed differences in message frequency, media usage, and daily communication activity. For the long-term analysis, although the number of chats differed between the pandemic and pre-pandemic years, comparisons focused on relative changes, as absolute values were less informative given the variations in data density over time.

The analysis revealed significant changes in WhatsApp communication behavior. **Short-term effects (March/April 2020 Lockdown):** * **Message Frequency:** A dramatic increase in daily message volume, reaching up to 2.58 times the pre-pandemic average. While 29% of chats showed a decrease, the majority (more than 45%) experienced at least a doubling of activity. * **Media Usage:** The overall share of media messages (images, videos, audio, etc.) increased by over 18%. Specific increases were seen in video and location messages, while contact messages decreased. * **Daily Communication Activity:** A shift in peak communication time from the evening to midday, with increased activity between 9 am and 2 pm and a decrease in evening hours. Increased nighttime messaging (12 am to 3 am) was also observed. **Long-term effects (Pandemic Year):** * **Message Frequency:** While the massive spike in March/April 2020 subsided, overall average daily messages per chat remained higher in the pandemic year compared to the pre-pandemic year. * **Media Usage:** Media usage largely returned to pre-pandemic levels; however, a notable decrease in location and contact messages persisted. Documents increased significantly indicating increased professional or educational usage. * **Daily Communication Activity:** The midday peak and increased nighttime communication activity persisted throughout the pandemic year, indicating a lasting shift in daily communication patterns. * **Regularity of Communication:** A significant increase (almost doubled) in the proportion of chats with very regular daily message patterns (no exceptional high days) indicating a shift towards more consistent communication, likely due to reduced in-person interaction.

The findings strongly support the hypothesis that the COVID-19 lockdown and the subsequent pandemic significantly altered WhatsApp communication behavior. The short-term effects, especially the massive increase in message frequency during the lockdown, reflect the immediate response to social isolation and increased reliance on digital communication. The persistent shift towards midday communication likely reflects changes in work and educational patterns, while the increased nighttime messaging might be associated with psychological impacts of lockdown measures, including sleep disturbances. The shift towards more regular communication suggests that digital communication, particularly via WhatsApp, has become a more integral part of daily routines, complementing or even replacing some forms of in-person interaction. These results have important implications for both behavioral scientists and network infrastructure providers, highlighting the need to account for changing digital usage patterns in future pandemic responses.

This study provides novel insights into the impact of the COVID-19 pandemic on WhatsApp communication behavior, demonstrating both short-term and long-lasting changes. The significant increases in message volume and shifts in daily communication patterns highlight the importance of digital communication during periods of social distancing. The observed shift towards more regular messaging patterns suggests a potential long-term integration of digital communication into social habits. Further research should explore the long-term societal implications of these shifts and examine whether these patterns persist or revert to pre-pandemic levels. Investigating other MIM applications is also crucial for obtaining more generalized insights.

The study relies on a voluntary dataset; thus, the sample might not be fully representative of the entire WhatsApp user population. The lack of demographic data on the users and their geographic locations limits more granular analyses of how regional variations in lockdown measures or cultural differences might have influenced communication behavior. Further research could address these limitations by employing more representative sampling methods and incorporating detailed user demographic information.