Internalising an externality for a free merit good I am researching vaccinations as a merit good and I am focusing on an article which discusses how some people are rejecting one of the COVID vaccines because of misinformation about how it may be less effective than the other vaccine. Can this externality be internalised since the vaccine is free to those receiving it because for example, with the flu vaccine the externality can be internalised by providing people with a voucher to receive a free vaccine however the COVID vaccines are already free. If not, is there any other way in which I can discuss how this can be done?
Article Link - https://www.theguardian.com/world/2021/feb/25/acceptance-problem-as-most-oxford-covid-jabs-delivered-to-eu-not-yet-used
Thanks
Even if the vaccine is free it is possible to additionally internalize the externality with subsidy. That is government can just pay people to take the vaccine.  Note, that even with a flu vaccine just providing voucher for a free vaccine might not be enough to fully internalize the positive externality (or it could be too much this is always case dependent).
For covid-19 specifically, there is an interesting recent paper on optimal covid-19 vaccine subsidies (among other things) by Goodkin-Gold et. al. (2020).  Their model shows that optimal subsidy will depend on the reproduction rate of the disease. Higher reproduction rate makes stronger case for subsidies, while if the reproduction rate it sufficiently low there might be no need for the subsidies at all. Moreover, the authors show that optimal level of subsidies also depends on competition in the industry. Specifically, they show that generally the more competitive industry is the greater case there will be for per unit subsidy.