culminated in military orders that mandated vaccinations for children before they were six months old and a general vaccination order. By the end of 1899 in Puerto Rico alone the U.S. military and other hired native vaccinators called practicantes, vaccinated an estimated 860,000 natives in a five-month period. This period began the United States' movement toward an expansion of medical practices that included "tropical medicine" in an attempt to protect the lives of soldiers abroad. Vietnam War During the Vietnam War, vaccination was necessary for soldiers to fight overseas. Because disease follows soldiers, they had to receive vaccines preventing cholera, influenza, measles, meningococcemia, Bubonic plague, poliovirus, smallpox, tetanus, diphtheria, typhoid, typhus, and yellow fever. However, the diseases mainly prevalent in Vietnam at this time were measles and polio. After arriving in Vietnam, the United States Military conducted the "Military Public Health Assistance Project". This public health program was a joint United States Military and Government of Vietnam concept to create or expand public medical facilities throughout South Vietnam. Local villages in Vietnam were inoculated. The United States military screened patients, dispensed medication, distributed clothing and food, and even passed out propaganda such as comic books. Information warfare An analysis of tweets from July 2014 through September 2017 revealed an active campaign on Twitter by the Internet Research Agency (IRA), a Russian troll farm accused of interference in the 2016 U.S. elections, to sow discord about the safety of vaccines. The campaign used sophisticated Twitter bots to amplify polarizing pro-vaccine and anti-vaccine messages, containing the hashtag #VaccinateUS, posted by IRA trolls. Confidence in vaccines varies over place and time and among different vaccines. The London School of Hygiene & Tropical Medicine's Vaccine Confidence Project in 2016 found that confidence was lower in Europe than in the rest of the world. Refusal of the MMR vaccine has increased in twelve European states since 2010. The project published a report in 2018 assessing vaccine hesitancy among the public in all the 28 EU member states and among general practitioners in ten of them. Younger adults in the survey had less confidence than older people. Confidence had risen in France, Greece, Italy, and Slovenia since 2015 but had fallen in the Czech Republic, Finland, Poland, and Sweden. 36% of the GPs surveyed in the Czech Republic and 25% of those in Slovakia did not agree that the MMR vaccine was safe. Most of the