out some 3,000 litres of it. On April 12, 1955, the vaccine was announced to be 60-90% effective against the three antigenic types of poliovirus and was immediately licensed for use in U.S. and Canada. In the U.S., licenses for vaccine production was granted to five pharmaceutical companies: Eli Lilly, Parke-Davis, Wyeth, Pitman-Moore, and Cutter. Shortly thereafter, in what became known as the Cutter incident, some batches of the vaccine from California's Cutter Laboratories led to an outbreak of polio and was immediately recalled. The Epidemic Intelligence Service of the Communicable Disease Center found that two production pools made by Cutter Labs contained live poliovirus. On May 7, the U.S. Surgeon General suspended the country's entire vaccine program. In Canada, Connaught's vaccine was the only version in use, and had demonstrated no cases of polio linked with its production. Therefore, Canadian use of the vaccine continued uninterrupted. Political and public health confidence in the vaccine north of the border during the Cutter incident helped pave the way for the U.S. to resume polio immunizations in July 1955. The Connaught Laboratories continued to improve and expand polio vaccine production during the latter half of the 1950s and into the early 1960s. Eradicating smallpox: 1960s-early 1970s Pre-1960s Smallpox is a highly contagious disease which has been fatal throughout most of recorded human history. Various techniques of variolation (protection against smallpox) have been documented globally, the most prominent records of established practice dating back to the Ming dynasty (present-day China) in the 15th century. In Europe, variolation was taken up in the 18th century via Constantinople. At the turn of the century into the 19th, a number of individuals including Benjamin Jesty and Edward Jenner began to demonstrate considerable success using a vaccine made from cowpox material. Variolation eventually declined as vaccines were shown to be effective and became better appreciated. In present-day Canada, the history of smallpox stretches back to European contact with indigenous peoples in the 17th century. Since the aboriginal demographic had no natural immunity, smallpox devastated populations that settlers made contact with. It spread first in New France near Tadoussac in 1616 and quickly reached tribes in the Maritimes, James Bay, and Great Lakes area. It reached the west coastal regions of Canada in the 1780s. On numerous occasions, the disease was used with official sanction by British troops as a form of germ warfare to suppress indigenous populations.