Mass Media Coverage and Vaccination Uptake: Evidence from the Demand for Meningococcal Vaccinations in Hungary

"A statistically significant and strong positive effect of media coverage is estimated on the uptake of all three types of meningococcal vaccinations."

While the role of social media has been studied in recent years as a determinant of the spread of anti-vaccination sentiments, less is known about the effect of mass media on vaccination uptake. Coverage with mandatory vaccinations is almost 100% in Hungary, but vaccination against invasive meningococcal disease (IMD) is elective and must be purchased in pharmacies (for later administration by a physician). IMD is a rare disease with rapid progression and a very high case-fatality ratio. As such, the effect of news is more likely identifiable compared to more common and less serious types of disease. This study aims to extend the knowledge base on determinants of vaccination demand, focusing on the influence of mass media on vaccination uptake in Hungary.

The researchers begin by laying the groundwork for the study. Demand for vaccination can be modelled as a comparison of benefits and costs related to the vaccination. The benefits originate from the avoidance of the disease, and the costs are the vaccination fee and non-monetary costs (e.g., side effects). If individuals are fully informed and rational, then neither the number of IMD cases nor their media coverage should affect the vaccination decision, unless the disease occurs in the neighbourhood of the decision-maker. The reason is that IMD is a very rare disease, and its occurrence somewhere has no effect on the probability of re-occurrence elsewhere.

There are two channels that can mediate the effect of media on behaviour, as outlined here:

1. If individuals are rational but not fully informed, then media news may provide relevant information for them. In this case, the media can exert an effect: Learning about the details of an IMD case or a death due to IMD might impact perceived severity of the disease, thus potentially increasing the observed benefits of the vaccination.
2. The news may have a direct behavioural effect if people pay attention to recent cases, or if they overestimate and overweight small probabilities. In the case of this so-called "bounded rationality" and imperfect information, media coverage of IMD might further affect vaccination demand. When faced with decisions under uncertainty (such as the decision on vaccination), people rely on heuristic principles to simplify the complex tasks of assessing likelihoods and predicting values. One such heuristic is availability - i.e., people assess the probability of an event by the ease at which occurrences of the event can be brought to mind.

The analysis is based on administrative county-level data on vaccination purchases (January 2009-December 2018) linked to indicators of media coverage of IMD and to administrative records of disease incidence. A note on media coverage: The researchers collected statistics of the online media coverage of the meningitis (agyhártyagyulladás, in Hungarian) and vaccination using web scraping techniques and looked at the four most popular online journals of Hungary. The majority of the articles refer to a specific county (typically, it is reported in which county the reported illness occurred); thus, the researchers can generate county-specific indicators of mass media coverage. To check whether individuals' web browsing (information searching) activity moves in line with the mass media coverage, the researchers also look at county-specific browsing history data from Google trends, again using the keyword of meningitis (agyhártyagyulladás).

The per capita demand for all three types of meningococcal vaccination tends to be higher in the capital city and in the western part of the country, which is typically economically richer and more developed. Children of more educated parents and those living in urban (typically wealthier) areas are also more likely to receive the Men C vaccination than are other children.

Over 2009-2018, the researchers found 100 meningitis-related articles, out of which 65 articles referred to a death case. Over the same time interval, 7 death cases due to IMD were covered by at least one of the analysed online journals. The vaccination rate jumped in 2017 for all three types of meningococcal vaccinations, coinciding with massive media coverage of the sudden death of a secondary school student in Budapest due to IMD in December 2016, followed by the death of a 2-year-old child in Borsod County.

Information search patterns closely follow the mass media coverage of meningitis, and there is a strong co-movement between vaccination uptake and online search intensity.

The researchers created an event-study type plot, beginning at the time when a meningitis-related online article was released, conditional on no article release the previous 6 months (to ensure a sufficient length of comparison period). Plotting the monthly vaccination rate as a function of the months elapsed since the news release, they saw 1.5- to 5-fold jumps in the rates of vaccination.

Net of monthly date effects and county effects, if a county-specific meningitis-related article is published, then that has a positive effect on the uptake of meningococcal vaccinations and on online search activities. This effect declines substantially after 1-2 months, except for the Men B vaccination, where the effect is estimated to persist even 4 months after the release of the article. The relative effect of online media coverage of meningitis is by far the largest on the Men ACWY vaccination (an additional 41 vaccinations compared to the mean of 36 per 100,000 people aged 0-17). These effects are slightly larger if the article refers to a death case. At the same time, the actual number of IMD death cases has no or even a negative (albeit small) effect on the demand for meningococcal vaccinations.

The findings indicate that the release of the news not only changes the timing of the vaccination (vaccinations are brought forward as a result of the news), but also leads to an increased total demand over a 5-month period. If country-wide time trends in vaccination demand are not taken into account, then the effect of mass media coverage on vaccination demand is overestimated.

The researchers say: "The results altogether imply that individuals are not perfectly informed about the severity or incidence of invasive meningococcal disease and/or that their vaccination decisions are not fully rational; otherwise, media coverage would not have an effect on vaccination demand."

Therefore, this study documents "the strong influence of mass media coverage of a disease on vaccination uptake. The findings point to the responsibility of the mass media in influencing health-related decisions, specifically, decisions related to vaccination....[T]he media coverage of invasive meningococcal disease is rather unbalanced and selective, and the excessive coverage of a single death event caused by invasive meningococcal disease leads to a surge in vaccination rates...Thus, to mitigate the influence of the selective and often misleading contents of the media, health specialists and policymakers should strive to provide objective and clear information related to the spread of diseases and vaccinations both in the mass media and other channels, such as information leaflets."

The researchers conclude by suggesting that the results have relevance to other institutional settings where a vaccination is not mandatory; in such settings, the individuals' decision of whether to vaccinate may be strongly influenced by disease- or vaccination-related news in the mass media.