April 28

Events - Science & Technology

1937day.year

South African medical researcher Max Theiler develops the yellow fever vaccine at the Rockefeller Foundation in New York City.

Max Theiler developed the first effective yellow fever vaccine at the Rockefeller Foundation, revolutionizing disease prevention. His work laid the foundation for global immunization efforts.
In April 1937, virologist Max Theiler announced the creation of a live-attenuated yellow fever vaccine, known as the 17D strain, at the Rockefeller Foundation in New York City. Theiler’s vaccine proved both safe and highly protective against the deadly virus in clinical trials and field use. This breakthrough dramatically reduced yellow fever outbreaks in Africa and South America, saving countless lives. Theiler’s work demonstrated the potential of live-attenuated vaccines and spurred advances in virology and immunology. For his pioneering achievements, Max Theiler received the Nobel Prize in Physiology or Medicine in 1951.
1937 South African Max Theiler yellow fever vaccine Rockefeller Foundation New York City
1947day.year

Thor Heyerdahl and five crew mates set out from Peru on the Kon-Tiki to demonstrate that Peruvian natives could have settled Polynesia.

Thor Heyerdahl launched the Kon-Tiki expedition to prove that prehistoric South American people could have reached Polynesia by raft. The daring journey captured global imagination.
In April 1947, Norwegian explorer Thor Heyerdahl and five companions set sail from Callao, Peru, on a balsa wood raft named Kon-Tiki. Heyerdahl aimed to demonstrate that ancient Peruvians could have drifted across the Pacific to populate Polynesia. Over 101 days at sea, the expedition covered more than 4,300 miles, relying solely on ocean currents and sails. Their successful arrival in the Tuamotu Archipelago challenged conventional theories of Pacific settlement. Heyerdahl’s story became a best-selling book and an Oscar-winning documentary, inspiring future generations of explorers.
1947 Thor Heyerdahl Peru Kon-Tiki Polynesia
1991day.year

Space Shuttle Discovery launches on STS-39, the first unclassified shuttle mission for the United States Department of Defense.

In 1991, Space Shuttle Discovery lifted off on mission STS-39, marking the first unclassified Department of Defense shuttle mission.
On April 28, 1991, NASA's Space Shuttle Discovery launched on STS-39, the first unclassified mission for the U.S. Department of Defense. The crew deployed and tested a suite of reconnaissance, communications, and environmental payloads over five days. The flight demonstrated the shuttle's versatility for both military and civilian applications without disclosing sensitive defense capabilities. Experiments ranged from atmospheric studies to satellite tracking. Discovery returned safely to Earth, delivering valuable data to scientific research and national security operations. STS-39 underscored the shuttle program's expanding role beyond pure scientific exploration.
1991 Space Shuttle Discovery STS-39 United States Department of Defense