§ Mr. Leach
asked the Secretary of State for War (1) why his medical advisers have reduced the period of the protective power of vaccination to two weeks; and whether the order that, where there is smallpox infection, men not vaccinated within the previous fortnight must be done again means that they are to be done every fortnight so long as the infection exists in the area in which they are stationed;
(2) whether he is aware that during an outbreak of smallpox in Egypt, in 1943–44, amongst Allied soldiers, 96 out of 100 cases were vaccinated persons and that 70 out of the 96 had been vaccinated successfully within two years and 16 of them between two and eight weeks before the disease started; that 13 out of 14 of the fatal cases in this outbreak had been vaccinated and one of them two months before he developed haemorrhagic smallpox; and whether, as these happenings indicate that even the most recent and successful vaccination does not protect from smallpox when that infection is present, what steps his medical advisers are taking.
§ Sir J. Grigg
It has never been claimed that vaccination confers 100 per cent. immunity against smallpox in all cases and under all conditions. The maximum degree of immunity is estimated to develop50W about 14 days after vaccination; thereafter it gradually wanes, but it remains effective, under normal conditions, for five years in the United Kingdom, and for three years in Egypt, where the risk of infection is somewhat greater. But during an epidemic, whenever it occurs, the virulence of the infecting agent is such that even the maximum degree of immunity conferred by immediate revaccination is not in every individual case sufficient to resist the disease. Nevertheless, experience has shown that the revaccination of all exposed to infection, coupled with the normal precautions of immediate isolation of infected persons and restriction of movement of possible "contacts," is successful in giving immunity to all but a small proportion and so in quelling an epidemic. Whether still further revaccination may at any time be necessary must be decided by the local commander, acting on the advice of his senior medical officer in the light of current conditions.