The yellow fever vaccine is not mandatory for visiting Manaus, but it is recommended for travelers planning to extend their trip into the forest. The vaccine should be taken at least 10 days before arrival. Originally, the vaccine was considered valid for 10 years; however, in 2013, the World Health Organization (WHO) announced that its immunity lasts for life. In other words, if you were vaccinated many years ago, a booster shot is not necessary.