Childhood vaccination rates often fall over the course of the immunization schedule. We study whether local mobile internet coverage reduces this decline, using data on about 113,000 children from India's National Family Health Survey (2019--21) matched to georeferenced maps of 3G network coverage. To address the non-random placement of 3G networks, we instrument coverage with terrain ruggedness, which raises the cost of deploying and maintaining network infrastructure. Comparing clusters within the same district, we find that 3G coverage has no detectable effect on the doses due in the first year of life but increases receipt of the doses due at 16--24 months. The effect emerges when children reach the age at which these doses become due. In a within-child design comparing earlier and later vaccinations of the same child, which removes all factors that affect both vaccinations equally, 3G coverage raises completion of the 16--24-month stage of the schedule but not of earlier stages. Taken together, the results point to information and coordination frictions as one barrier to completing vaccination in the second year of life.