ths, making disinfection of wards or sickrooms after the removal or death of a patient essential. Most victims are, however, infected by contact with an infected person by inhalation of the virus expelled in the breath or mouth spray.Despite the hardiness of the virus, smallpox is not a highly infectious disease; a patient does not usually infect more than one or two of his closest contacts. The great danger from the disease is that it can cause very mild attacks in vaccinated persons, and these persons can spread the fatal form of the disease to their contacts without knowing that they themselves have been infected. It is therefore essential in dealing with an outbreak to make thorough enquiry into all possible contacts of patients and to follow these contacts until it is certain they have escaped infection or to isolate them at once if they show any sign of infection.The smallpox virus exists in one main strain, variola major, and a vaccine prepared from variola major will also protect against the one or two other closely related strains, such as variola minor, which causes a much milder form of the disease. The availability of one single-type vaccine against all forms of clinical smallpox, combined with the absence of any reservoir of smallpox virus in nature, made possible the attempt by the World Health Organization to eradicate smallpox from the world. This immense project involved following all contacts of every case of smallpox and vaccinating them in time to prevent the spread of infection. The project is believed to have been successful. Smallpox is estimated to have caused 2,000,000 deaths in 1967. No cases were reported from 1977 to 1980, with the exception of two cases in England in 1978 whose source was virus in a laboratory. Routine smallpox vaccination has been discontinued in most countries, and the virus is to be kept in not more than four laboratories throughout the world, ready to make vaccine should it ever again be...
