No animal on Earth is more lethal to humans, killing over 600,000 people a year from malaria alone and up to a million when including other diseases like dengue fever and yellow fever: https://www.bbc.com/news/magazine-35408835

From article:

>The effort is one of several focused on addressing the mosquito-borne disease that kills over 600,000 each year, most of them children in Africa. The complicated structure and lifecycle of the malaria parasite has long stymied efforts to develop vaccines.
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>After decades of work, the only approved malaria vaccine, Mosquirix, made by British drugmaker GSK (GSK.L), was this year endorsed by the World Health Organization (WHO), but a lack of funding and commercial potential has thwarted GSK's capacity to produce as many doses as needed.