Epidemiology of Chikungunya Virus Infection in the Philippines

Background: Chikungunya virus (CHIKV) has circulated in the Philippines for more than six decades. Reviewing the evidence accumulated over this period provides an oppor-tunity to summarize its epidemiology and describe patterns of transmission over time. We systematically reviewed the epidemiology of CHIKV in the Philippines, integrating evidence on transmission, seroprevalence, diagnostics and molecular lineages. Methods: We followed PRISMA 2020 and searched PubMed and Embase to March 2026 for original studies reporting incidence, prevalence, seroprevalence, outbreak characteristics, or surveillance findings in human populations in the Philippines. Grey literature from the Department of Health (DOH) Epidemiology Bureau (2018–March 2026) was included separately. Findings were synthesized narratively because of substantial heterogeneity. Results: Sixteen studies and one national surveillance dataset were included. Serological reconstruction and prospective cohorts indicate approximately four major transmission waves over six decades, separated by intervals of about 17 years. Each wave infected an estimated 23% (16–37%) of remaining susceptible, while more than half remained sus-ceptible thereafter. In Cebu, incidence declined from 12.32 to 2.84 infections per 100 person-years as neutralizing-antibody prevalence increased from 28% to 42%; only about one in five infections was symptomatic. National surveillance recorded 12,662 cases from 2018 to early 2026, including 722 laboratory-confirmed; three deaths. The Asian genotype predominated during the 2011–2013 epidemic, while the Indian Ocean lineage viruses were detected in southern Mindanao. Conclusions: Transmission of CHIKV in the Phil-ippines appears to follow a periodic, recurrent pattern, with outbreaks occurring as population susceptibility accumulates following periods of low-level transmission. Pe-riodic arboviral serosurveys and testing of acute febrile illness are needed to better characterize CHIKV epidemiology in the Philippines.