Vaccination uptake increased in the 1990s. However, after doubts about the safety of the MMR vaccine surfaced in public debate, the increase became smaller among children of parents with lower levels of education – and the gap has persisted for decades. This means that protection against disease remains unevenly distributed, calling for more targeted communication, says a researcher.
When misinformation undermines confidence in vaccines, it is not only a question of how many people choose to opt out but of how protection against disease is distributed across society.
A new study in Denmark shows that the risk of not receiving the MMR vaccination after concerns about the vaccine’s safety emerged was linked to parents’ level of education.
The nationwide registry study was based on more than 1.2 million children born between 1990 and 2011 and linked vaccination status with parents’ educational level at the individual level.
The researchers followed each child to determine whether they received their first MMR dose and compared vaccination uptake before and after three key events to examine whether differences between educational groups changed over time. The study itself cannot establish a direct causal link.
“It is about gaining a broader understanding of how misinformation can affect different groups in different ways. If some groups are affected more than others, it is crucial that we understand how to communicate facts specifically to them,” explains Vibeke Tornhøj Christensen, senior researcher at VIVE – the Danish Centre for Social Science Research.
The research has been published in Social Science & Medicine.
Three events tested the emerging social pattern
To examine whether the social pattern changed, the researchers identified three specific events during which doubts about the MMR vaccine were widely debated in public.
The first event was a radio programme in 1993 in which a mother publicly linked the MMR vaccine to autism. The broadcast sparked a nationwide debate – and in the years that followed, vaccination uptake began to develop along social lines.
The second event was Andrew Wakefield’s 1998 scientific article, which claimed a link between the MMR vaccine and autism.
The third event was the retraction of the article in 2010, after serious methodological and ethical problems were uncovered.
After each event, the researchers estimated whether differences in vaccination rates between educational groups changed statistically over time – and whether trends diverged between the groups. This enabled them to test whether the pattern repeated itself or changed character in response to new waves of information.
“The idea is that the more education you have, the better equipped you may be to assess what is information and what is misinformation. That can provide a stronger basis for action – including making informed decisions about vaccinating your children,” she explains.
A small gap – with lasting consequences
The study shows that before 1993, there was no fixed social pattern in who was vaccinated by educational group.
It was only after the media event in 1993 that a difference gradually began to emerge – and this became the starting point of the pattern that characterised uptake in the following decades.
The difference was modest – between two and five percentage points – but it appeared in the mid-1990s and persisted in the decades that followed.
The later international events – Wakefield’s study in 1998 and its retraction in 2010 – did not significantly alter the trajectory that had been set after 1993. In that sense, they served to indirectly test the pattern’s stability: the social gap did not change systematically even after the claim was scientifically rejected.
Although the difference amounts to only two to five percentage points, it means that the least educated groups often fall below the critical threshold of 90% – at which outbreaks of disease become more likely.
“The difference that emerged after 1993 persists throughout the period, but we do not see the pattern in uptake changing in connection with Andrew Wakefield’s article or when it became clear that there is no link between the vaccine and autism. The results suggest that scepticism does not spread uncontrollably – but neither does it disappear. It appears to be concentrated in certain groups – even after the claim of a link between the vaccine and autism was scientifically rejected,” says Vibeke Tornhøj Christensen.
When protection is unevenly distributed
Overall, the results show that misinformation can be associated with more than temporary fluctuations in trust – it can coincide with a lasting shift in how risk is distributed across society and with persistent differences in protection against disease.
In Denmark, the analysis shows that the first domestic media event in 1993 coincided with the emergence of the social difference – but the study cannot demonstrate that the event caused it.
In addition, the findings indicate that some groups are more vulnerable to misinformation than others – and that communication efforts therefore need to be adapted accordingly.
“The question is how we ensure that information reaches every corner of society. For some, it makes sense to channel it through the Danish Health Authority, whereas others may need to be reached in different ways. We need to recognise that information does not work in the same way for everyone if we are to secure support above 90% in all groups,” says Vibeke Tornhøj Christensen.
