Two letters to the editor of the New England Journal of Medicine point to changes in Bordetella pertussis, the bacteria responsible for whooping cough as the potential cause for the recent uptick in instances of the illness in recent years.

Authors of one of the letters note the first-reported occurrence of pertactin-negative variants of B. pertussis in the United States. Pertactin is one of the components involved in the body’s immunity against the bacteria. Its absence indicates that at least one component of existing vaccinations is ineffective against these pertactin-negative strains.

They note that “regions should be evaluated to determine whether our finding is a local event or represents a more widespread shift in B. pertussis strains. An understanding of the epidemiology and virulence of pertactin-negative variants is crucial to developing the next generation of pertussis vaccines.”

In the second letter, clinicians from the Oregon Health Authority in Portland discovered that children vaccinated with the whole-cell pertussis vaccines (diphtheria–tetanus–whole-cell pertussis, or DTwP) had significantly fewer instances of whooping cough than those who received the acellular pertussis vaccines (diphtheria–tetanus–acellular pertussis, or DTaP).

The authors acknowledge the switch to DtaP “was motivated by the higher rates of adverse events with DTwP,” but note “the balance between vaccine side effects and effectiveness needs to be considered in developing and implementing recommendations on pertussis vaccination, particularly in light of recent outbreaks of pertussis.”