For instance, patent laws may have an influence. In the private sector if you want patent protection, a certain market exclusivity that rewards the investments that the private company makes in research, that can attract funds. For instance, the United States quite recently passed a patent extension, particularly to encourage research on biologic medication.
The same sort of incentive measure could be used not only for biologic medication, but also perhaps for vaccines. Research on vaccines takes much longer than research to develop medication.