4. Discussion
To the best of our knowledge, this is the first study, both in human and
veterinary medicine, that investigates the dynamics of vaccination
compliance and the factors which influence its deterioration after an
epidemic. The results of this study show that vaccination compliance
diminishes as time elapses from an epidemic. The main factor influencing
compliance deterioration is the reduction of the farmers’ perceived
social pressures to vaccinate. Together with availability of manpower
for vaccination and price considerations, these are the major causes of
reduction in vaccination compliance. These findings open an opportunity
for interventions to mitigate the compliance deterioration of
vaccination for epidemic diseases.
Vaccination compliance is a well-studied issue in human medicine (Betsch
et al., 2018 & Brewer et al., 2017) and recently is being studied also
in veterinary medicine (Elbres et
al., 2010; Eschle et al., 2020 &
Gehrig et al., 2019). Like other studies in which the TPB was used to
explain and predict behaviour, we found that the three main constructs -
attitude, subjective norms and PBC- all predicted the intention to
vaccinate (Agarwal, 2014 & Schmid
et al., 2017).
Both in human medicine studies (with a particular focus on Influenza
vaccination) and veterinary medicine studies (e.g. vaccination against
Bluetongue disease in cattle), the intention and/or behaviour to
vaccinate are significantly associated with the attitude of the decision
maker towards vaccination (Schmid et al., 2017 & Sok et al., 2016).
Similar to the current study, these studies show a significant
association of social pressures with intention. The most important
normative referent is the physician/veterinarian. At the level of
attitudinal beliefs, there are also similarities. In the study of Sok et
al. (2015) who surveyed Dutch farmers, it was indicated that the most
influential attitudinal beliefs relate to being insured both
economically and psychologically from the disease consequences. In our
study, the most influential beliefs related to the vaccine economical
benefit, reducing the severity of clinical signs, receiving money from
the insurance company, having peace of mind and reducing the number of
disease cases. However, as opposed to Sok et el. we haven’t found a
significant association of intention to vaccinate with the relative risk
attitude, or the yearly milk quota (another measure of the size of the
herd) (Sok et al., 2018). This might stem from the low variance among
the Israeli dairy farmers and herds which did not enable enough power
for such a comparison.
The main novel contribution of the current study is to the understanding
of vaccination compliance deterioration as time elapses from an
epidemic. Given the consequences of LSD epidemics, one would expect that
previous experiences with the disease should have been associated with
higher compliance. Surprisingly, we did not find such direct
association. However we did find lower vaccination compliance in the
Centre of Israel, which was the least affected area during previous LSD
epidemics. This may indicate again on the influence of the existing
norms in the area on intention to vaccinate. When comparing of farmers’
direct and indirect measurements of attitude, subjective norms and PBC
before and after the epidemic of 2019 we found both higher perceived
social pressure to vaccinate and higher intention to vaccinate, after
the 2019 epidemic compared to before. This result should however
interpreted cautiously, as the situation right after the epidemic in
2019 is not the exact situation in 2016. In 2016, vaccination became
voluntary three years after the last epidemic. We also lack the exact
picture of the actual reduction in perceived social pressures to
vaccinate after the epidemic.
According to the TPB, the PBC construct moderates the interaction
between the intention and the behaviour
(Armitage et al., 2010). This is
supported by our results, as we found that among farmers who intended to
vaccinate, PBC was the main differentiating factor between farmers who
vaccinated and those who eventually didn’t vaccinate. The 50% reduction
that we found from intention to behaviour is indeed within the range
described before for different behaviours
(Sheeran, 2002) but high compared
to human vaccination studies
(Brewer et al., 2011).
Another important finding in our study is that past vaccination is a
reliable and strong predictor of future vaccination. The multivariable
analysis on the data of the 566 dairy farms insured by the ‘Hachaklait’
organization indicates that farmers who vaccinated their herd both in
2017 and 2018 were about 120 times more likely to vaccinate also in 2019
than a farmer with no history of vaccination. This finding was
independent of any other demographical characteristics. However, this
past behaviour itself can be the result of certain attitudinal,
normative and control beliefs (Brewer et al., 2017). This finding
implies that most of the effort to increase vaccine compliance should be
focused on farmers who withdrew from vaccination or never vaccinated
their herd against the disease.
The current study suffers from several limitations. One limitation is
the small sample size of farmers who answered the TPB questionnaire.
These questionnaires were part of a larger study in which the behaviour
of farmers was studied to four other livestock diseases. Ideally, each
farmer would have been surveyed on all five diseases. However, since
that would have made the questionnaire exceptionally long, we preferred
to ask each farmer randomly about one disease. Another possible
limitation is that the study does not follow the same persons over time
and thus does not show directly the personal change of farmers’ beliefs.
Rather we interviewed different farmers at different times and compared
the answers. It should be noted, however, that interviewing the same
persons at different times may create response biases due to the gained
experience by the farmers who repeatedly answer the same questionnaires
(Wetzel et al., 2016). It would be, however, interesting to perform
similar studies using a repeated questioning methodology as well and to
compare the results with the results of the current study.