No 20 - 2012

Under-reporting of childhood vaccinations

In order to estimate the degree of under-reporting of vaccinations to the Childhood Vaccination Database, SSI has performed a questionnaire survey among children who are not registered as having received the DTaP-IPV booster vaccination. This vaccine, which is administered at the age of five years, has an estimated 82% coverage, the lowest of all the vaccines recommended by the Danish Childhood Vaccination Programme, EPI-NEWS 20/11. The survey also included the remaining childhood vaccinations: DTaP-IPV/-Hib1, 2 and 3 administered at the age of 3, 5 and 12 months, respectively, and MMR1 administered at 15 months.

Respondents were asked where their child had received the vaccinations, and parents' explanations as to why any vaccinations had not been given were noted. The study also examined if a tetanus vaccination given at a casualty ward reduced the probability of receiving the DTaP-IPV booster vaccination.

The vaccinations included in the Danish Childhood Vaccination Programme are administered by GPs. Vaccinations are recorded in the child's yellow vaccination card and reported to the Danish Childhood Vaccination Database. Specifically, the information is collected via the administrative service codes used by GPs when reporting vaccinations for reimbursement. The administrative service code reflects type and number of vaccination given and is reported electronically to the National Danish Health Insurance along with the vaccination date and the civil registration number (CPR number) of the vaccinee. This information is used to calculate the coverage of the Childhood Vaccination Programme vaccines.

Study design

A number of children born in the 2000-2003 period who had not received DTaP-IPV vaccination according to the Childhood Vaccination Database were identified and selected randomly from the CPR Register. A questionnaire and a consent form were sent to the children's parents. All selected children were 7-10 years old at the time contact was made with their parents.

Results

A questionnaire was sent to 574 parents, 386 of whom responded either by returning a completed questionnaire in a pre-paid envelope (32%), by completing an electronic questionnaire (3%), by participating in a telephone interview (58%) or by authorizing staff to contact their GP directly (8%). A total of 134 persons (34%) did not respond and 54 (9%) declined to participate in the survey.

A total of 272 (70%) of the respondents stated that their child had received the DTaP-IPV booster vaccination, and 121 (44%) were able to provide the date the vaccination had been administered. The survey thus documents that under-reporting to the database does occur.

A total of 70 parents (18%) stated that their child had not received the DTaP-IPV booster vaccination. A total of 26 (7% of all respondents) stated that they "forgot about it", 11 (3% of all respondents) stated that they "did not want the vaccination", one (<1% of all included) stated "did not have time to have my child vaccinated", one (<1% of all included) replied "my child was ill at the time the vaccination was scheduled and I have not rescheduled" and 21 (5%) stated "other reasons".

In the vast majority of the cases in which the parents stated that their child had received the DTaP-IPV booster vaccination, the child had been vaccinated at the GP (89%).

A total of 6% stated that their child had been vaccinated abroad, 4% did not provide information about the place of vaccination, and <1% stated that their child had been vaccinated at a hospital. 

Tetanus vaccination at an ER did not affect the share of children who had received the DTaP-IPV booster vaccination. 

Also for the remaining childhood vaccinations, DTaP-IPV/Hib1, 2 and 3 and MMR1, it was stated that 5-6% of vaccinations were given abroad and that <1% had been administered at a hospital.

Furthermore, additional vaccinations which had not been reported to the Childhood Vaccination Database were recorded, where a number of parents stated that their children had been vaccinated at the GP’s office, but there was no record of the vaccination in the Childhood Vaccination Database. This was the case for two children with the DTaP-IPV/Hib1 vaccination (approx. 1%), seven children with the DTaP-IPV/Hib2 vaccination (approx. 4%), 24 children with the DTaP-IPV/Hib3 vaccination (approx. 14%) and ten children with the MMR1 vaccination (approx. 6%).  

Consequences of under-reporting

If the described under-reporting is taken into account when calculating the vaccination coverage of the DTaP-IPV booster vaccination from the Childhood Vaccination Database data, coverage increases from 82% - conservatively estimated - to 85.1-86.3%. Furthermore, it is estimated that DTaP-IPV/Hib1 coverage may be adjusted upwards from 86.0% to 90.4%, DTaP-IPV/Hib2 from 86.5% to 90.6%, DTaP-IPV/Hib3 from 86.0% to 89.5%, and MMR1 from 86.4% to 90.7%.

Commentary

The Danish Childhood Vaccination Database is an important tool for the assessment of the vaccination coverage of the Danish Childhood Vaccination Programme vaccines. The survey described herein documents that under-reporting to the database occurs. This means that the calculated vaccination coverage for DTaP-IPV booster vaccination is underestimated by 3.1 to 4.3 percentage points.

It is essential to improve vaccination registration by ensuring that GPs report all administered vaccinations using the correct administrative service codes.

When the Danish Vaccination Register (DVR) is implemented in 2013, all administered vaccines must be recorded, including travel-associated vaccinations. Furthermore, all citizens will have access to see and add vaccinations to their personal vaccination card. It will also be possible for citizens and GPs to add and/or change the vaccines recorded for their underage children. Vaccinations given abroad comprise 5-6% of the non-recorded vaccinations and cannot currently be recorded in the Danish Childhood Vaccination Database, but in the future, it will be possible to add such vaccinations.

Functionality improvements such as a more flexible recording of vaccinations, citizens’ access to their own vaccinations, allowing them to add missing vaccinations and/or change incorrectly recorded vaccinations make the DVR a potential improvement of the monitoring of vaccination coverage in Denmark. 

(O.P. Wójcik, K. Mølbak, P. Valentiner-Branth, Dept. of Infectious Disease Epidemiology, J. Simonsen, Dept. of Epidemiology Research)

Department of Epidemiology changes name

In connection with a reorganisation of the SSI in March 2012, the Department of Epidemiology changed name to Department of Infectious Disease Epidemiology.

16 May 2012