Effect of a proactive childhood vaccination reminder system on vaccination coverage and uptake in Denmark: A...

In August 2019, Denmark implemented a proactive childhood vaccination reminder system. This study aimed to assess the effect of the introduction of this vaccination reminder system on vaccination coverage and uptake of the first four childhood vaccinations, namely the tetanus, diphtheria, acellular pertussis, polio, haemophilus influenzae type b (Hib)-infection vaccination (DTaP-IPV/Hib) recommended at three, five and twelve months as well as mumps, measles, rubella vaccination (MMR1) recommended at 15 months.

This was a retrospective register-based cohort study based on two birth cohorts: children born in January 2018 (i.e. control group) and January 2022 (i.e. intervention group). All children that lived in Denmark and were alive during the entire study period were included. Children were followed-up from two weeks before to six weeks after each scheduled vaccination. The end of the study period was therefore at 16.5 months. Differences in vaccination status were tested at six weeks after scheduled vaccination. The median days to vaccination were calculated and compared between the two cohorts. Kaplan Meier curves and logrank tests were used to compare vaccination uptake over time between the two cohorts. Logistic regression analyses tested for differences in vaccination coverage at six weeks after scheduled vaccination between the study groups. Sensitivity analyses were conducted using alternative birth cohorts.

The vaccination coverage at six weeks after scheduled vaccination was higher for children in the intervention cohort for all vaccinations, except the second diphtheria-tetanus-pertussis-polio-Hib vaccine (DTaP-IPV/Hib2) given at 5 months. Fewer children in the intervention cohort were unvaccinated (3.4 % vs 1.3%3 %; p < 0.001) and more children had received all three DTaP-IPV/Hib vaccinations at the end of the study period (88.3 % versus 79.0 %; p < 0.001). Children in the intervention group were significantly more likely to have been vaccinated at six weeks after scheduled vaccination for all vaccinations except DTaP-IPV/Hib2, compared to the control group.

This study indicated that the children vaccinated under the proactive vaccination reminder system did have a higher vaccination coverage for three out of four investigated childhood vaccinations and a somewhat quicker vaccination uptake than children vaccinated before the introduction of the reminder system.