RFK Jr.'s key advisor petitioned to revoke approval of the polio vaccine. Photos show the US's last outbreak.

• A lawyer advising Robert F. Kennedy Jr. wants the FDA to revoke approval of the polio vaccine.
• Before vaccines were available in 1955, polio caused 15,000 cases of paralysis in the US each year. 
• The US eliminated the disease in 1979, but unvaccinated travelers can still carry polio in.

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Some health experts are concerned that polio could make a comeback...