Resurgence of Respiratory Viruses Following Relaxation of COVID-19 Non-Pharmaceutical Interventions in Northern Tanzania

The COVID-19 pandemic, caused by SARS-CoV-2, prompted widespread implementation of non-pharmaceutical interventions (NPIs) such as mask-wearing, hand hygiene, social distancing, and restrictions on gatherings to limit viral transmission in the absence of vaccines and specific treatments. While effective in controlling COVID-19, these measures also disrupted the circulation of other respiratory pathogens, potentially creating temporary immunity gaps. This study aimed to assess the impact of NPIs and seasonal variation on the prevalence and seasonality of viral respiratory infections in Northern Tanzania. A cross-sectional hospital-based study was conducted at Kilimanjaro Christian Medical Centre (KCMC) and Mawenzi Regional Referral Hospital (MRRH), including 183 patients presenting with acute respiratory tract infection (ARTI) symptoms between January-December 2022 and January-June 2024. Archived and fresh oropharyngeal-nasopharyngeal samples were tested using multiplex and singleplex real-time RT-PCR assays for SARS-CoV-2, influenza A and B, RSV, human parainfluenza viruses, adenovirus, rhinovirus, and human metapneumovirus. Data analysis was performed using STATA v17, with statistical significance set at p < 0.05. Viral prevalence, including mono-infections and co-infections, was significantly higher in the post-pandemic period, with Influenza A (H3), RSV, HMPV, HPIV1, and adenovirus. SARS-CoV-2 prevalence declined in 2024, while co-infections with other viruses increased. Seasonal analysis indicated that dry seasons consistently recorded the highest viral circulation, whereas the short and long rainy seasons showed minimal activity during the pandemic. We therefore conclude that relaxation of NPIs was associated with increased respiratory virus activity. These findings indicates a complex interplay between public health interventions, viral interference, environmental factors, and host immunity in shaping respiratory virus epidemiology. Sustained surveillance and adaptive public health strategies are needed to anticipate outbreaks, guide control measures, and reduce the impact of seasonal respiratory viral infections, especially in resource-limited settings.