Routine immunisation coverage in the context of seasonal influenza vaccine introduction for children in Nakuru and Mombasa counties in Kenya, 2019-21: an observational study.

Abstract

Data on how the introduction of seasonal influenza vaccination for children might affect the coverage for other routine childhood immunisations are scarce. We assessed how introducing a new influenza vaccine for children aged 6-23 months in two counties in Kenya (Mombasa and Nakuru) affected the coverage rate for the diphtheria-tetanus-pertussis-hepatitis B-Haemophilus influenzae type b (pentavalent [Penta]) vaccine, measles-rubella (MR) vaccine, and vitamin A supplementation. In this observational study, we compared data from two sub-counties in Kenya that implemented a year-round (ie, annual routine immunisation) influenza vaccine delivery strategy and two that implemented a campaign-mode delivery strategy with data from two control sub-counties where no influenza vaccine was provided. We used facility-level immunisation tally sheets to obtain counts of monthly vaccine and supplement doses given and monthly summary data to estimate the coverage rates. We collected data for 1 year before (from Nov 1, 2018 to Oct 31, 2019) and during the seasonal influenza vaccine demonstration period (from Nov 1, 2019 to Oct 31, 2021). We used negative binomial Bayesian models, adjusted for time period (before vs during the demonstration project), facility ownership, and level of health facility, to compare coverage rates for routine immunisations between health facilities that participated in the influenza vaccine demonstration project and those that did not. Our study included 64 health facilities: 28 (44%) year-round, 12 (19%) campaign-mode, and 24 (38%) control sites. 42 (66%) of the facilities were level 2 (secondary) and 36 (56%) facilities were government owned. Before and during the influenza vaccine demonstration period, coverage rates for Penta doses one, two, and three and MR dose one were more than 65% in all the intervention sites; for comparison, in the control sites coverage was 62·9% (95% CI 62·1-63·8) for Penta dose one and 64·0% (63·1-64·9) for MR dose one. The coverage rate for MR dose one was significantly higher in the year-round sites versus the control sites across the timespan of the study (adjusted rate ratio 1·38, 95% CI 1·27-1·49), and the coverage rates for Penta dose two (aRR 0·24 [0·05-0·65]) and MR dose one (aRR 0·98 [0·82-0·97]) were significantly lower in the campaign-mode sites versus the control sites. There were no other significant differences in coverage rates for other routine vaccine or supplementation doses in the intervention (year-round and campaign-mode) versus the control sites. When comparing coverage before and during implementation of the influenza vaccination project, MR dose one coverage at the campaign-mode sites was significantly lower during the demonstration than before (rate ratio [RR] 0·75 [95% CI 0·70-0·80]), and MR dose two (RR 1·15, 1·06-1·24) and vitamin A dose two (RR 2·14 [2·00-2·29]) at the campaign-mode sites were significantly higher; none of the other changes before and during implementation at the other sites or for other doses were statistically significant. The introduction of seasonal influenza vaccine for eligible children had a minimal effect on the uptake for routine vaccines in Kenya's Expanded Programme on Immunization. The Task Force for Global Health and The Centers for Disease Control and Prevention.