From my book, Vaccines: truth, lies, and controversy: “The immune system is immensely complicated, and it is not possible to predict which nonspecific effects a targeted vaccine might have. Vaccines can affect nontargeted infectious diseases both positively and negatively. Danish professor Peter Aaby has done ground-breaking research in this area spanning 40 years.14 His group has published many papers that provide support to their hypothesis that live attenuated vaccines decrease total mortality while nonlive vaccines increase total mortality. The measles vaccine, for example, decreases mortality much more than what can be explained by its effect on preventing measles. The sequence of vaccinations also seems to be important for total mortality, and it is best to end with a live vaccine. Such observations do not render decision making about vaccines easy.
Bacillus Calmette-Guérin (BCG) for tuberculosis and the measles vaccine probably reduce mortality from pneumonia and sepsis. In contrast, the combined diphtheria, tetanus, and pertussis (DTP) vaccine is suspected to double overall mortality in low-income countries, which is worrying because the vaccine apparently induces tolerance and increases the risk of unrelated infections, in particular respiratory infections, which are bigger killers than the targeted diseases in such settings15 (see more about this in Chapter 8). These findings did not make Aaby popular at WHO headquarters. Public health messages become difficult when such totally unexpected results appear and become supported by subsequent studies.”
In 2019, I wrote an expert report, Effect of DTP vaccines on mortality in children in low-income countries. This was because a WHO systematic review from 2014 had assessed the effect of three vaccines on total mortality in infants and children: BCG (Bacille Calmette-Guérin), DTP (diphtheria, tetanus, and pertussis) and measles. I found serious flaws in the WHO review while I confirmed Aaby’s findings that the DTP vaccine doubled mortality in low-income countries. WHO also found that the DTP vaccine increased mortality but in trying to explain away what they found, they violated basic scientific principles. You can read my expert report here.