One argument against incentives is that the mere fact of offering a payment might be inferred to signal that the vaccine is unsafe. Two state-of-the-art studies estimate the effect of financial incentives on trust in the vaccines and find none. A limitation of these studies is that trust in the vaccine was already established at the time that incentives came to be offered. If applied to a vaccine that had just received approval from medical licencing authorities, financial incentives might have a negative impact on trust.
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A team of researchers have published an impressive set of studies in Science (Campos-Mercade et al., 2022) and Nature (Schneider et al., 2023) that conclude: “Contrary to prominent warnings in the academic literature and public debate, our work suggests that modest financial incentives for vaccination can be used without worries about grave unintended consequences.”
Now consider the next pandemic: you are a policymaker with responsibility for public health. The circumstances you face are as follows. There is a vaccine that has already been approved by medical licencing authorities as safe and effective in granting immunity to the disease. The bad news is that you can already see that the disease is snowballing through another country’s population and it is only a matter of days before it hits your shores.
The question you are faced with is whether or not to offer your population financial incentives to get vaccinated with the newly approved vaccine.
At first glance, the data from the Campos-Mercade et al. (2022) paper and from the Schneider et al. (2023) papers seem diagnostic for answering this question. They show in nationally representative data from Sweden that financial incentives are effective in increasing uptake of vaccination (unlike various nudges they tested). Moreover, paying people to get the first dose of a vaccine did not induce any measurable negative effect over the longer term. For instance, the hypotheses that financial incentives for a first dose would reduce trust and perceptions of safety and efficacy were not supported.
But the Swedish data are answering a substantively different question than that which you are asking yourself as a policy maker. You are interested in what will happen if you offer a financial incentive to everyone in your population when first rolling out a newly approved vaccine. The Swedish data answers what happened when, months after a population has first started receiving the vaccine,a random subsample of the population was offered a cash incentive to get the vaccine.
To see why this distinction matters, consider one concern regarding the use of incentives to promote vaccine uptake. It is that offering incentives will be inferred by some members of the public to signal that the vaccine is unsafe e.g. “the government believes that taking the vaccine requires compensation and so they must believe that the risk associated with the vaccine is especially high.”
The Swedish randomised controlled trial (RCT) data shows that in the absence of a cash incentive, 73% of people come forward for a vaccine. That baseline result implies that there was already a high level of trust in the vaccine among the Swedish population. This high rate of trust is not surprising because the Covid vaccine had been intensely scrutinized for side-effects. In March 2021 – two months before the Swedish RCT went to field – Norway suspended use of the AstraZeneca vaccine when a small number of vaccinated individuals experienced bloodclots. Within a day, this move was front-page news across Europe and led to suspensions of the AstraZeneca vaccine in other countries. Notwithstanding this scare, intentions to receive a vaccine against Covid remained high, which indicates a robust level of trust in the Covid vaccines (Comerford et al., 2021). In short, the sample recruited into the Swedish RCT had already formed their judgments of the trustworthiness of the vaccine ever before some of them were offered a financial incentive.
The Swedish RCT began too late to test whether financial incentives cause negative inferences regarding the efficacy and safety of the vaccine. The same limitation applies to the second study in Schneider et al. (2023). In the second study, researchers examined the impact of informing residents in specific US states that in their state a financial incentive is offered for getting vaccinated (the authors document that this fact was not widely known among the populations of those states). As with the Swedish RCT, there were no negative effects of learning that financial incentives are being offered for getting vaccinated on perceived efficacy, safety, and trust related to vaccination. But, as with in the Swedish RCT, states only began offering financial incentives relatively late in the roll-out of the vaccines. Schneider et al. (2023) point to the example of California, which began offering a “Vax for the Win” program in May 2021, four months after it had started its vaccinating program.
Conclusions
The contribution of this comment is to clarify that an important question that looks as though it was addressed by two seminal papers in prestigious scientific journals has not in fact been addressed. We still do not know if a newly approved vaccine (or medical procedure) will be inferred as less safe if its use is incentivised.
It is not that the existing research is worthless on this question. At the very least, Schneider et al.’s result offer a recommendation on how financial incentives can be delivered. Implicitly their results recommend offering the vaccine without any incentives in the first instance and then, once trust in the vaccine has been established, offering financial incentives as a means to motivate the hold-outs to get vaccinated.
Of course, that recommendation relies on the vaccine being sufficiently safe and efficacious that it garners trust in the first place. It also relies on the safety and efficacy of the vaccine being persuasively communicated to the public. Neither of these outcomes are assured. To the extent that either does not obtain, the provision of financial incentives might backfire. If trust in the vaccine is low to begin with then a public health authority that offers financial incentives is taking substantial and untested risks. The less important of these risks is causing further damage to trust in the vaccine. The more substantial risk is causing damage to the credibility of the public health authority itself.
References:
Campos-Mercade, P., Meier, A. N., Schneider, F. H., Meier, S., Pope, D., & Wengström, E. (2021). Monetary incentives increase COVID-19 vaccinations. Science, 374(6569), 879-882.
Comerford, D., Olivarius, O., Bell, D., Dawson, A., Brown, T., McGregor, L., … & Douglas, E. (2021). Did negative news regarding the Oxford AstraZeneca vaccine end in vaccine hesitancy? A repeated cross-section event study from the UK.
Schneider, F. H., Campos-Mercade, P., Meier, S., Pope, D., Wengström, E., & Meier, A. N. (2023). Financial incentives for vaccination do not have negative unintended consequences. Nature, 1-8.
[1] Economics Division and Behavioural Science Centre, University of Stirling, FK9 4LA. David.comerford@stir.ac.uk