Smallpox is considered to be a leading factor in the European conquest of the Americas, as the accidental introduction of the disease wiped out entire populations of existing New World civilizations. While variolation was sometimes used to build up resistance to the disease, it had dangerous side effects. Then Edward Jenner introduced vaccination in 1797. King Charles IV had lost family members to smallpox, and was excited to use Jenner's technique to protect his subjects. To fight smallpox in the Spanish colonies, he sent a ship on a vaccination expedition under the supervision of Francisco Javier Balmis in 1803. But how to make the "raw material" last long enough for a ship to sail around the world? The expedition included medical professionals and 22 orphans between the ages of eight and ten.
During the journey, the vaccine was kept viable by passing it from arm to arm in orphaned children, who were brought along expressly for that purpose and remained under the care of the orphanage's director. This expedition was the first large scale mass vaccination of its kind. The historic legacy of this pioneering event in international health should be revisited in the current era of persistent inequalities in global health.
The Balmis Expedition stopped at the Caribbean Islands, Venezuela, Colombia, Mexico, the Philippines, Macau, and Canton over the next three years. Thousands of people were vaccinated, although some places already had the vaccine and others rejected it. It would be almost 200 more years before smallpox was eradicated, but the philanthropical expedition did much to spread the concept of the vaccine. Read about the Balmis Expedition in an article from the journal Clinical Infectious Diseases.
PS: In case you were wondering what happened to the orphans,
Happily they were settled in Mexico, educated at the expense of the Spanish treasury, and eventually adopted by local families.