The Trump administration’s proposed budget for the coming fiscal year eliminates funding for programs that provide lifesaving vaccines around the world, including immunizations for polio.

The budget proposal, submitted to Congress last week, proposes to eliminate the Centers for Disease Control and Prevention’s global health unit, effectively shutting down its $230 million immunization program: $180 million for polio eradication and the rest for measles and other vaccine-preventable diseases. The budget plan also withdraws financial support for Gavi, the international vaccine alliance that purchases vaccines for children in developing countries.

Overall, the budget request explicitly follows President Trump’s America First policy, slashing funds for global health programs that fight H.I.V. and malaria, and cutting support altogether to fight diseases that affect only poorer countries.

“The request eliminates funding for programs that do not make Americans safer, such as family planning and reproductive health, neglected tropical diseases, and nonemergency nutrition,” the proposal said.

Many public health experts said that such thinking is flawed because infectious diseases routinely breach borders. The United States is battling multiple measles outbreaks, prompting the C.D.C. last week to warn travelers about the risks of contracting measles. Each of those outbreaks began with a case of measles contracted by an international traveler.

“Every single measles case this year is related to actual importations of the virus into the United States,” said Dr. Walter Orenstein, associate director of the Emory Vaccine Center and a former director of the United States’ Immunization Program.