Q: Why is pertussis (whooping cough) spreading when most children receive the DTaP vaccine?
Medically reviewed by Sang Hyun Ahn, MD
Content edited by Myeongchan Kim, MD
This post is a dramatization of a question and answer session experienced by our actual medical reviewers. Please note that this content is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
Question:
I am curious about why pertussis (whooping cough) is currently spreading. The vast majority of children receive the DTaP vaccine as part of their basic immunizations before starting school. Even if the antibody formation rate isn't exactly 100%, it should be very close. Given this high vaccination rate, why are we seeing an outbreak of pertussis?
Answer:
It is completely understandable to wonder why pertussis (whooping cough) outbreaks occur despite such high vaccination rates. Here is a breakdown of the main reasons behind the recent spread:
Waning Immunity Over Time
• The immunity provided by the DTaP vaccine gradually decreases 5 to 10 years after vaccination.
• As a result, adolescents and adults experience weakened immunity, allowing them to contract and spread the infection.
• This is why a Tdap booster shot is highly recommended for 11 to 12-year-olds and during pregnancy.
Limitations of the Acellular Vaccine (DTaP)
• The acellular vaccines used since the 1990s have fewer side effects than older whole-cell vaccines, but the duration of the immunity they provide is shorter.
• The vaccine is more effective at preventing severe disease rather than completely blocking infection.
• Even vaccinated individuals can contract a mild form of the illness and transmit it to others.
Improved Diagnostic Technology
• Advances in testing, such as PCR testing, now allow us to detect mild or atypical cases that would have been completely missed in the past.
• It is important to consider whether the outbreak is due to an actual increase in cases or simply an increase in successful diagnoses.
Unvaccinated Populations
• Infants under 2 months old are too young to have received their first vaccine dose, making them highly vulnerable.
• In some regions or communities, vaccine refusal can lower the overall vaccination rate, compromising herd immunity.
Bacterial Mutations
• Some variants of the pertussis bacteria (Bordetella pertussis) show slight differences from the vaccine antigens.
• While this does not mean the bacteria completely evades the immune system, it can slightly reduce the vaccine's overall effectiveness.
Current Recommendations:
• Ensure completion of the basic infant immunization series (5 doses of DTaP).
• Receive the Tdap booster shot at 11 to 12 years of age.
• Pregnant women should get the Tdap vaccine between 27 and 36 weeks of gestation to pass protective antibodies to their newborns.
• Family members, caregivers, and healthcare workers caring for infants should also consider getting a Tdap booster.
Summary:
The primary reasons for pertussis outbreaks include waning immunity over time, the shorter immune duration of the acellular vaccine, and adolescents or adults spreading mild, unrecognized infections to vulnerable infants. However, vaccines remain highly effective at preventing severe illness and death. Please consult your pediatrician or primary care physician to ensure that you and your family are up to date on all routine and booster vaccinations.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
