No. But one may want a yellow fever vaccination if we stop at Iguazu Falls (rather than just flyover) as a precautionary measure.

From the Brazilian Consulate (San Francisco) website re: Yellow Fever vaccination:

FAQ 16. I heard that I need a Yellow Fever Vaccination Certificate to enter Brazil. Is it true?

The International Immunization Certificate against yellow fever will only be required from international travelers coming from countries which pose a risk of international dissemination. Currently there are no countries posing such risk. (Please see FAQ 1402 at www.anvisa.gov.br). Nevertheless, yellow fever vaccination is recommended if applicant intends to visit one of the following regions in Brazil: Acre, Amapá, Amazonas, Federal District, Goiás, Maranhão, Mato Grosso, Mato Grosso do Sul, Pará, Rondônia, Roraima, Tocantins.