In 2013, the number of girls vaccinated for human papillomavirus (HPV) in Denmark plummeted following negative media coverage that caused uncertainty among parents. A new study reveals that this controversy also affected measles, mumps and rubella (MMR) vaccination in Denmark’s childhood vaccination programme. It is still uncertain whether the decline in MMR vaccination primarily resulted from general scepticism about vaccination or whether parents were awaiting clarification about the HPV vaccination so that their daughters could receive both vaccinations at the same time.
Vaccination can be controversial – perhaps because it is not like medicine that cures an illness. The discussion about whether vaccination does more harm than good escalated to new heights in Denmark when many girls in 2013–2015 developed seemingly inexplicable illnesses that individual doctors, parents and the mass media rapidly attributed to HPV vaccination. The controversy caused the percentage of girls vaccinated for HPV to drop from 79% to 46%.
“As we investigated this decline, we discovered the interesting fact that introducing HPV vaccination free of charge in 2009 was associated with a 5 percentage point increase in girls vaccinated for MMR, so that more girls got MMR vaccination than boys. The HPV vaccination controversy from 2013 onwards caused the proportion of children getting vaccinated for MMR to decline – especially for girls, falling by 6 percentage points compared with boys, so that girls and boys again had similar vaccination rates. Our study may not fully explain the reasons for these changes, but the decline seemed to result from increasing scepticism about vaccination and from especially busy parents simply waiting for clarification about HPV vaccination so they could take their children to get two shots at the same time,” explains a main author, Mette Ejrnæs, Professor, Department of Economics, University of Copenhagen.
Gender difference eliminated
The new study of 827,716 girls and boys is based on data for 1991–2017 from Denmark’s registries. In Denmark, children are offered MMR vaccination – receiving the first dose of vaccine at 15 months and the second dose at age 12 years. Until 2009, 85% of boys’ parents and 86% of girls’ parents accepted this offer, but this changed in 2009 when 12-year-old girls were offered HPV vaccine free of charge.
“After 2009, the MMR vaccination rate increased from 86% to 88% for the girls but declined for boys in the same period. We imagine that many of the girls who otherwise might not be vaccinated have busy parents and that the percentage increased because many of these parents suddenly had two reasons for getting a doctor’s appointment. In any case, the increase was only among girls, so this interpretation is obvious,” says Mette Ejrnæs.
In later years, the percentages of vaccinated boys and girls continued to differ by 4–6 percentage points, but that difference changed again in 2013, when the controversy about HPV vaccination started and uncertainty spread about whether this vaccination is dangerous.
“In addition to the significant decline in the percentage of girls vaccinated for HPV, the number of girls vaccinated for MMR dropped from 88% to 80%. The percentage of boys vaccinated for MMR dropped slightly to 79%. So the difference between the sexes was eliminated, which we partly attribute to the fact that many girls’ parents no longer had two reasons to get a doctor’s appointment combined with generally increasing scepticism about vaccination,” explains Mette Ejrnæs.
Timing can backfire
Concomitant vaccination for HPV and MMR thus appears to increase overall vaccination rates. However, reduced demand for one vaccination may reduce the rates of other types of vaccination and undermine the coverage of a country’s vaccination programme.
“The new research is not only important for the future of Denmark’s childhood vaccination programme. Childhood vaccination programmes are among the most cost-effective public health interventions worldwide. WHO has therefore identified vaccination uncertainty and resistance as one of the leading threats to global public health,” says Mette Ejrnæs.
Most countries have high coverage for many childhood vaccinations, and yet many countries are struggling to achieve the sufficiently high rates needed to control and potentially eliminate serious illnesses.
“This study shows that the timing of vaccination is important. Offering HPV vaccination to 12-year-old girls increased the coverage of MMR vaccination and similarly reduced coverage as the controversy heightened. So having more concomitant vaccinations seems like a good idea, but uncertainty about a specific vaccination can spread to the other concomitant vaccinations,” concludes Mette Ejrnæs.
“The contagious nature of a vaccine scare: how the introduction of HPV vaccination lifted and eroded MMR vaccination in Denmark” has been published in Vaccine. In 2017, the Novo Nordisk Foundation awarded a grant to another main author, Mette Gørtz, for the project Behavioural Responses to Health Innovations and the Consequences for Socioeconomic Outcomes.
