No 25/26 - 2021

Study of the causes for a low vaccination coverage observed in the childhood vaccination programme

To enable specific and targeted vaccination initiatives, the Department of Infectious Disease Epidemiology and Prevention at Statens Serum Institut has studied which groups of children have a lower vaccination coverage in the childhood vaccination programme than same-aged children in the general population.

Overall, the coverage of the Danish childhood vaccination programme is high, but inequality in society is reflected in the vaccination coverage. In 2018, the Danish Government decided to allocate funds for new vaccination-related initiatives, and this study forms part of these initiatives. For vaccines comprised by the Danish vaccination programme, the objective of the study was to identify groups of children with a lower vaccination coverage than same-aged children in the general population and to establish possible causes (determinants) for the lack of vaccination aiming to enable specific and targeted vaccination efforts.

Data and methods

A study was conducted based on national data from the following registers: the Danish Civil Registration Register (CPR Register), the Danish Vaccination Register (DVR) and data from Statistics Denmark. The study was divided into three sub-studies focusing on the following vaccines; diphtheria-tetanus-whooping cough-haemophilus influenzae type B (DTaP-IPV/Hib) including the five-year booster, measles-mumps-rubella (MMR) and human papilloma virus (HPV) in girls.

For each sub-study, a cross-sectional study was conducted and the study population was characterised according to vaccination coverage for the possible determinants. Furthermore, the vaccination coverage was calculated for each vaccine and each determinant. The effect of possible determinants of a low vaccination coverage was analysed using the Cox's proportional hazard regression model, one by one and adjusted for the remaining determinants resulting in a hazard ratio and corresponding 95% confidence intervals. Additionally, the vaccination coverage at municipal and regional levels was analysed in the cross-sectional study. For HPV, vaccination coverage was also analysed at school level. For the sub-populations “descendants” and “immigrants”, differences in vaccination coverage between countries of origin were studied, and the effect on vaccination coverage of the parents’ Danish proficiency was also studied in the cross-sectional study.

Several reasons for a lower vaccination coverage

The following birth cohorts (and number of children) were included in the studies: DTaP-IPV/Hib1 2001-2016 (1,013,878 children), DTaP-IPV4 2001-2011 (five-year booster, 719,823), MMR1 2001-2015 (952,625), MMR2 2005-2012 (516,268), HPV1 and HPV2 2001-2004 (128,356). All children were residing in Denmark when the data was collected (13 September 2019). A significant difference (p value < 0.001) was found between the percentage of vaccinated children for all vaccinations for the following determinants: birth cohort, cohabiting adults (both parents, one of their parents, others), number of siblings, origin, age of the mother at the birth of the child, parents’ level of education, parents’ occupation and family income. Furthermore, for HPV the type of school (public school, private school, special school) and whether the girl had previously received the five-year booster (DTaP-IPV4). Generally, coverage was higher for DTaP-IPV/HIB1, MMR1 and HPV1 than for the five-year booster (DTaP-IPV4), MMR2 and HPV2 for all determinants.

The findings show a lower probability for children to be vaccinated if they did not live with any of their parents, attended a special school, attended a private school, were immigrants, had mothers younger than 25 years or older than 34 years when the child was born, had not followed the childhood vaccination programme (i.e. those who had not received the five-year booster), or were children of parents with a low educational level or parents who were non-employed and/or had a low income. For only children, the probability of being vaccinated was higher for the vaccines that are given early in the child’s life (DTaP-IPV/HIB1 and MMR1) than for vaccines given later (HPV).

Small geographical differences and a focus on immigrants

Across the 98 municipalities of Denmark, the geographical spread in vaccination coverage was greatest for vaccinations placed late in the childhood vaccination programme. No pattern was observed in vaccination coverage with respect to the size of the municipality or if the municipality comprised large cities, but a trend towards an east/west divide was seen. No regional differences were observed in vaccination coverage for DTaP-IPV and MMR, but for HPV the coverage was lower in Region Zealand and the Capital Region, whereas the Region of Southern Denmark and the Region of Central Jutland recorded the highest coverage.

The majority of the immigrants in the study were from Syria, Poland, Romania and Greenland, and they all had a lower vaccination coverage than the general population. Lacking Danish proficiencies was associated with a lower vaccination coverage.

Schools with a low number of 14-year-old girls had a wider range of HPV-vaccination coverage than schools with many girls. Among the schools with the lowest coverage were many anthroposophic schools and international schools.

Recommended initiatives

We recommend a continued focus on reducing the inequality in society in general, as inequality is reflected in the vaccination coverage. Furthermore, we recommend focus on children living away from home, attending special schools and for immigrants in general, but in particular for immigrants from Syria, Poland, Rumania and Greenland. As a minimum, the measures targeting immigrants should comprise comprehensible information about the Danish childhood vaccination programme, specifying that vaccination is free of charge.

Measures aiming to increase the coverage of vaccinations comprised by the childhood vaccination programme should be initiated early, as a 50% higher HPV-vaccination coverage is recorded among girls who have followed the full childhood vaccination programme. Furthermore, we recommend targeted measures in municipalities with a low vaccination coverage, possibly based on regional cooperation and also continuation and possibly expansion of the reminder scheme.

The report includes a summary, and summaries of the findings for each vaccine. The report is in Danish and can be found here.

(S. Voss, S. K. Nørgaard, P. Valentiner-Branth, Department of Infectious Disease Epidemiology and Prevention)

MRSA 2020

2020 recorded a total of 2,883 new MRSA cases, Figure 1, which was a 21% reduction compared with 2019 (3,657), EPI-NEWS no. 23, 2020. The reduction was expected due to the COVID-19-induced travel restrictions, limitations on social contacts and reduced number of healthcare contacts.

For a detailed epidemiological description of the 2020 incidence, please see the 2020 annual MRSA report.

In 2020, a total of 31 outbreaks were registered at hospitals, nursing homes and other institutions, comprising a total of 129 MRSA cases. Seven of the outbreaks occurred in neonatal departments, comprising a total of 59 cases. Additionally, eight outbreaks occurred at other hospital departments (a total of 20 patients), and seven outbreaks were recorded in nursing homes (17 cases).

The number of MRSA cases of the livestock type (CC398) constituted 32% (n = 931) of the total number of cases (31% of the total number of cases in 2019). 2020 saw 95 persons with no livestock contact who became infected with livestock MRSA CC398 (86 persons in 2019 and 87 persons in 2018). This is a small increase, but spreading of livestock MRSA CC398 in the general population does not seem to follow an increasing trend despite the fact that more persons with livestock contact have tested positive over the years. 2020 saw a total of ten cases of livestock MRSA CC398 bacteraemia. None of these patients died within 30 days after the sampling date.

In 351 (12%) cases, MRSA had been acquired abroad, which is considerably lower than in the previous years. Travel activities in Denmark were also heavily reduced due to COVID-19.

Furthermore, at decline was seen in community-acquired MRSA, which may also be explained by reference to restrictions on personal contact, but also by a reduced number of visits to general practitioners.

(A. Petersen, A.R. Larsen, Bacteria, Fungi and Parasites, B. Kristensen, T. Urth, Y. Canales, Department of Infectious Disease Epidemiology and Prevention)