Indicators of the National Immunization Program for children under one year old: time trend in Maranhão, Brazil, 2010 to 2021.

We aimed to analyze the trend of indicators of the National Immunization Program (acronym in Portuguese. PNI) in children under one-year-old and classify municipalities regarding the risk of transmission of vaccine-preventable diseases (RTVPD) in Maranhão from 2010 to 2021. This ecological time series study was based on secondary data on vaccination coverage (VC). vaccination coverage homogeneity (VCH). proportion of abandonment (PA). and RTVPD. with state coverage for vaccines in the national children's calendar. Prais-Winsten regression estimated trends (α=5%) and the indicators' annual percentage change (APC). We identified fluctuating and discrepant VC between vaccines. with a decreasing trend (p < 0.01). except those against Hepatitis B (p = 0.709) and oral human rotavirus (p = 0.143). The sharpest falls were for Yellow Fever (APC = 12.24%) and BCG (APC = 12.25%) vaccines. All VCH rates were lower than expected. with a drop from 2014 and APC between 5.75% (Pneumococcal 10; p = 0.033) and 14.02% (Poliomyelitis; p < 0.01). We observed an increasing trend in PA for Pentavalent (APC = 4.91%; p < 0.01) and Poliomyelitis (APC = 3.55%; p < 0.01). We identified an increase of 52.54% in the proportion of municipalities in Maranhão from 2015 to 2021. with extremely high (p = 0.025) and high (p = 0.028) RTVPD. The PNI indicators deteriorated. reaffirming the susceptibility to the emergence of vaccine-preventable diseases.