WHO marks 25th anniversary of last naturally acquired smallpox case

On Oct. 26, 1977, the world's last case of naturally acquired smallpox was reported in Somalia. Three years later, the World Health Organization declared the world free of naturally occurring smallpox. Eradication of the disease, a campaign that began in 1966, was considered an unprecedented accomplishment. In Canada, an average of 2263 cases of smallpox were reported yearly between 1924 and 1929, and the last endemic cases occurred in 1946. The last case of smallpox imported to Canada was reported in 1962.

Figure. Smallpox: Canada's last outbreak occurred in 1946 Photo by: WHO

Smallpox (see CMAJ 2001;165[10]:1380) is transmitted via person-to-person contact, mainly through airborne respiratory droplets. It can also be transmitted through contact with infected clothing or bedding. The mortality rate for the most virulent strains is about 30%.

Until the disease was eradicated, each infected person infected approximately 5 other people. The cessation of vaccination programs means the infection rate in today's population, particularly among those under age 35, could be much higher.

In light of the potential use of the smallpox virus as a bioterrorism agent, the possibility of vaccination programs is being discussed for the first time in 31 years. In 2001, the federal government had 365 000 doses of the vaccine on hand. — CMAJ