Peter Aaby - Biography#

Education/training: 1974 Mag. Scient., Social Anthropology, University of Copenhagen

Since 1978, PA has built a large health and demographic surveillance system in Guinea-Bissau. Under-5 child mortality was 500/1000 in 1978. PA showed that contrary to expectations, the high measles case fatality (25%) was not due to malnutrition, but to intensity of exposure as secondary cases within the family. Intensity of exposure was subsequently shown to explain severity in many childhood infections including pertussis, chickenpox, polio and RSV. Though trained in anthropology PA was awarded a Dr. Med. Sc. degree, University of Copenhagen, for this work on measles infection in 1988.

PA’s team was the first to introduce measles vaccine (MV) in Bissau in 1979. The MV campaign reduced overall child mortality by two-thirds, an effect not explained by prevention of measles infection. This led to a series of discoveries contradicting the current paradigm for vaccines: Vaccines affect susceptibility to unrelated infections and these non-specific effects (NSEs) are far more important for child survival than the specific preventive effects. The following patterns have emerged: Live vaccines, including MV, BCG, oral polio vaccine (OPV) and smallpox vaccination, have major beneficial NSEs, whereas non-live vaccines, including DTP, Inactivated polio vaccine (IPV), hepatitis B vaccine (HBV), Pentavalent (DTP+HBV+Hib) and RTS,S malaria vaccine have negative effects for female survival.

PA’s team also discovered that boosting with live vaccines, as happens in eradication campaigns, enhance the beneficial NSEs. Under-5 mortality has now declined to 65/1000. The numerous eradication campaigns with OPV and MV are responsible for much of this decline. Christine S Benn and PA have also found that maternal priming enhances the beneficial NSEs of both BCG and MV.

An important implication of the NSEs is that if we eradicate a disease and then stop the corresponding live vaccine, mortality and morbidity may increase again. It was shown in both Guinea-Bissau and Denmark that smallpox vaccination had beneficial effects on survival long after smallpox was eradicated. Similar situations are likely to occur with polio (to be eradicated 2024) and measles (within the next 10-15 years); once these live vaccines are stopped, we may see large increases in child mortality.

A new paradigm for vaccines is emerging emphasizing that vaccines can have impact not only on the target infection(s) but also on the general resistance towards other pathogens. Pursuing this paradigm will lead to major reductions in child mortality in low-income countries and to health care cost-savings in rich countries.