This conversation was led by Christine Stabell Benn, MD, PhD, DMSc, MAE, Professor in Global Health at the University of Southern Denmark. Unknown to most people, vaccines were never tested for their effects on overall health before being introduced; everybody was so certain that vaccines only affect the target infection that it did not seem necessary. Our population-based studies in one of the world’s poorest countries, Guinea-Bissau, have revealed that this assumption was too simplistic. It has become clear that vaccines do not only protect against the target infection; they also affect the susceptibility to other infections. We have called these effects the “non-specific effects” of vaccines. Immunological studies have now provided a biological mechanism by showing that vaccines modulate the innate immune system. The focus on non-specific effects has also revealed that the effect of vaccines depends markedly on parental priming with the same pathogen.
The findings challenge our understanding of vaccines and the immune system. The implications are far-reaching: hundreds of thousands of lives could be saved every year in low-income countries and morbidity and health expenditure could be reduced significantly in high-income countries, by taking non-specific effects of vaccines into account when designing vaccination programs. In relation to the ongoing COVID-19 pandemic, the findings have the following implications: 1) We might be able to use existing live vaccines against COVID-19; 2) We cannot assume that just because they protect against COVID-19, the new COVID-19 vaccines will improve overall health. To be sure we need to conduct post-marketing trials to assess their overall health effects (the sum of their specific and non-specific effects).
- Wenner Moyer 2019, “Vaccines Reimagined”
- Chumakov et al. 2020, “Can existing live vaccines prevent COVID-19?”