Vaz and colleagues1 used regression analysis to conclude that mandatory vaccination led to increased vaccination coverage and reduced measles incidence in Europe. They compared 21 countries classified without mandatory vaccination and 7 countries classified with: Bulgaria, Czech Republic, Hungary, Latvia, Poland, Slovenia, and Slovakia. The authors found positive association between vaccination coverage and size of monetary fines imposed for not taking children for vaccination.
We have several reservations on the methodology and analysis. While the 7 countries have indeed reported high coverage rates for several decades, we do not believe that mandatory vaccination is the primary reason. Instead, strong immunization programs is the major factor, with fines rarely levied in the countries with mandates. In Hungary, for example, an important reason for high coverage is that pediatric nurses make home visits to new parents, keep children on record, and follow-up with defaulters.2
Regression analysis only shows correlations and not causal effects. Rutter warns against papers like the one by Vaz et al: “From an early point in their training, all behavioral scientists are taught that statistically significant correlations do not necessarily mean any kind of causative effect. Nevertheless, the literature is full of studies [containing direct or implied causal conclusions] that are exclusively based on correlational evidence.” (p. 377).3
Regression results are only valid if the model holds. Unfortunately, the authors do not show any metrics to validate their confounders. This is particularly concerning given the small sample size of 7 countries with mandatory vaccination and a relatively large number of controlled variables. Moreover, Table 2 shows considerable outliers in the non-mandatory group, but no adjustments are made.
Differences in coverage between the 2 groups seemed only to be significant before 2013. Indeed, when we ran the analysis with the addition of 2017 and 2018 data, the result does not seem to hold. Measles coverage decreased to 93% in Bulgaria, Poland, and Slovenia in 2018, compared with 96% to 98% in earlier years.4
In addition, we are concerned about the country categorization. The authors classified countries with mandatory vaccination if measles and pertussis vaccines were mandated, but Belgium, Cyprus, France, Greece, Italy, and Malta mandate other vaccines, particularly polio.5 As polio vaccine is combined with pertussis in most European countries, pertussis vaccine is effectively also mandated. Hence, those 6 countries should have been classified as having mandatory vaccination, which would, of course, have led to different results.
We question the authors’ conclusion that mandatory vaccination has the potential to decrease negative impacts of vaccine-preventable diseases. In our opinion, mandatory vaccination is primarily a political intervention put forward as a quick fix without appreciating and seeking to relieve the root causes of low vaccination coverage. Several of the countries with the best measles control in Europe do not have mandatory vaccination (Netherlands, Norway, Sweden).4,5 They have inclusive vaccination programs with follow-up systems for parents who fall outside of the normative behavior. We believe that a public health system should be built on trust and quality services. Threats of penalties do not foster trust.
CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.