The yellow fever vaccine is a safe and effective immunization that protects against yellow fever, a viral disease transmitted by mosquitoes. The vaccine contains a weakened form of the virus, which stimulates the immune system to produce antibodies. A single dose typically provides long-lasting immunity, often for life. Vaccination is especially important for travelers to areas where yellow fever is endemic, particularly in parts of Africa and South America. Some countries require proof of vaccination for entry, making it essential for those planning to visit these regions to get vaccinated before their trip.