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Non-specific effects of vaccines (also called “heterologous effects" or "off-target effects") are effects which go beyond the specific protective effects against the targeted diseases. Non-specific effects can be strongly beneficial, increasing protection against non-targeted infections, but also at times negative, increasing susceptibility to non-targeted infections. This depends on both the vaccine and the sex of the infant. All live attenuated vaccines studied so far (BCG vaccine, measles vaccine, oral polio vaccine, smallpox vaccine) have been shown to reduce mortality more than can be explained by prevention of the targeted infections. In contrast, inactivated vaccines (diphtheria-tetanus-pertussis vaccine (DTP), hepatitis B vaccine, inactivated polio vaccine) may increase overall mortality despite providing protection against the target diseases. These effects may be long-lasting, at least up to the time point where a new type of vaccine is given. The non-specific effects can be very pronounced, with significant effects on overall mortality and morbidity. In a situation with herd immunity to the target disease, the non-specific effects can be more important for overall health than the specific vaccine effects.〔 The non-specific effects should not be confused with the side effects of vaccines (such as local reactions at the side of vaccination or general reactions such as fever, head ache or rash, which usually resolve within days to weeks - or in rare cases anaphylaxis). Rather, non-specific effects represent a form of general immunomodulation, with important consequences for the immune system’s ability to handle subsequent challenges. It is estimated that millions of child deaths in low income countries could be prevented every year if the non-specific effects of vaccines were taken into consideration in immunization programs. ==History== The hypothesis that vaccines have non-specific effects was formulated in the early 1990s by Peter Aaby at the Bandim Health Project() in West Africa. The first indication of the importance of the non-specific effects of vaccines came in a series of randomized controlled trials (RCTs) in the late 1980s. It was tested whether a high-titer (high-dose) measles vaccine (HTMV) given at 4–6 months of age was as effective against measles infection as the standard measles vaccine (MV) given at 9 months of age. Early administration of the HTMV prevented measles infection just as effectively as did the standard MV given at 9 months of age. However, early administration of the HTMV was associated with twofold ''higher'' overall mortality among females (there was no difference in mortality for males). In other words the girls given HTMV died more often despite having the same protection against measles as the infants given standard MV. The discovery forced WHO to withdraw the HTMV in 1992. This first observation that vaccines could protect against the target disease but at the same time affect mortality after infection with other pathogens, in a sex-differential manner, led to several further studies showing that other vaccines might also have such nonspecific effects. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Non-specific effect of vaccines」の詳細全文を読む スポンサード リンク
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