5. Conclusion

It is irrefutable that the worldwide incidence of severe pertussis cases is rising. Nearly 90% of all instances of deaths caused by pertussis occur in infants younger than 4 months of age and are caused by fatal pertussis pneumonia due to PTx activity [72], which highlights the need to inhibit PTx during an acute infection. Over the past few years, the scientific community has responded by initiating studies focused on a better understanding of virulence factors, like PTx, transmission dynamics, and host immune reactions, which can provide a foundation for the generation of a new vaccine but can also guide improvements in the use of current vaccines. It is clear that a control of pertussis requires a durable protection against disease and disruption of transmission. The two types of vaccines available, wPV and aPV, are effective in preventing the disease, but the immunity developed by each wane over time, even more rapidly with aPV, which should encourage countries in which wPV is still in use, not to switch to aPV. Further, transmission from vaccinated individuals is possible since B. pertussis can still colonize their respiratory tracts. Improvements to both types are in development, but it will be several years before their widespread use. In the interim, expansions in the use of the current vaccines have been proposed. Cocoon vaccination programs, which are controversial in their effectiveness, rely on generating herd immunity to protect young infants by vaccinating individuals with close contact. In contrast, immunization with aPV during pregnancy can reduce the incidence of severe and deadly pertussis in neonates. However, there are concerns that the antibodies raised from the maternal immunization can interfere with the immune response in the child to their primary vaccination. All approaches under development would benefit from

<sup>1</sup> DTaP, Tdap, and Td are all similar vaccines, given for the same diseases at different times of life. Depending on the age, certain amounts of vaccine components are administered. Typing uppercase and lowercase letters denotes the component of the vaccine and the quantities in it. Uppercase letters in abbreviations denote undiluted doses of diphtheria (D), tetanus (T), and pertussis (P) toxoids. The lowercase letters d and p denote reduced doses of diphtheria and pertussis toxoids used in formulations for adolescents and adults. The letter a in the DTaP and Tdap vaccines means acellular.

a more detailed surveillance program to determine the rates of symptomatic and asymptomatic infections as well as an examination of the genetic diversity of B. pertussis strains in circulation to better understand methods to prevent the impacts of infection.
