Data collected through routine syndromic surveillance for influenza-like illness in the Micronesian United States-affiliated Pacific Islands highlighted out-of-season influenza outbreaks in the spring of 2019. This report describes the data collected through the World Health Organization’s Pacific Syndromic Surveillance System for the Commonwealth of the Northern Mariana Islands (CNMI), Guam, the Federated States of Micronesia (FSM) and the Republic of the Marshall Islands (RMI). Compared with historical data, more cases of influenza-like illness were observed in all four islands described here, with the highest number reported in Guam in week 9, CNMI and FSM in week 15, and RMI in week 19. The outbreaks predominantly affected those aged <20 years, with evidence from CNMI and RMI suggesting higher attack rates among those who were unvaccinated. Cases confirmed by laboratory testing suggested that influenza B was predominant, with 83% (99/120) of subtyped specimens classified as influenza B/Victoria during January–May 2019. These outbreaks occurred after the usual influenza season and were consistent with transmission patterns in Eastern Asia rather than those in Oceania or the United States of America, the areas typically associated with the United States-affiliated Pacific Islands due to their geographical proximity to Oceania and political affiliation with the United States of America. A plausible epidemiological route of introduction may be the high levels of international tourism from Eastern Asian countries recorded during these periods of increased influenza B/Victoria circulation. This report demonstrates the value of year-round surveillance for communicable diseases and underscores the importance of seasonal influenza vaccination, particularly among younger age groups.

Objective: The Commonwealth of the Northern Mariana Islands (CNMI) is a remote Pacific island territory with a population of 47 329 that successfully prevented the significant introduction of coronavirus disease (COVID-19) until late 2021. This study documents how the response to the introduction of COVID-19 in CNMI in 2021 was conducted with limited resources without overwhelming local clinical capacity or compromising health service delivery for the population. Methods: Data from COVID-19 case investigations, contact tracing, the Commonwealth’s immunization registry and whole genome sequencing were collated and analysed as part of this study. Results: Between 26 March 2020 and 31 December 2021, 3281 cases and 14 deaths due to COVID-19 were reported in CNMI (case fatality rate, 0.4%). While notification rates were highest among younger age groups, hospitalization and mortality rates were disproportionately greater among those aged >50 years and among the unvaccinated. The first widespread community transmission in CNMI was detected in October 2021, with genomic epidemiology and contact tracing data indicating a single introduction event involving the AY.25 lineage and subsequent rapid community spread. Vaccination coverage was high before widespread transmission occurred in October 2021 and increased further over the study period. Discussion: Robust preparedness and strong leadership generated resilience within the public health sector such that COVID-19 did not overwhelm CNMI’s health system as it did in other jurisdictions and countries around the world. At no point was hospital capacity exceeded, and all patients received adequate care without the need for health-care rationing.