Evidence shows Tdap booster in pregnant women reduces the risk of whooping cough in infants

Whooping cough, also known as pertussis, is a highly contagious respiratory disease caused by the bacteria Bordetella pertussis. When an infected person coughs or sneezes, droplets of the bacteria spread through the air, allowing the disease to pass from person to person when they breathe in these infected droplets.

The DTaP vaccine helps children under the age of seven develop immunity against diphtheria, tetanus, and pertussis. Tdap is a booster vaccine given to individuals above the age of seven to provide continued protection against these diseases, since the efficacy of the DTaP vaccine wanes over time.

Claims that DTaP and Tdap vaccines cause harm circulate as part of vaccine misinformation on social media platforms. In one Facebook post from 23 April 2024, a social media user claimed that the Tdap vaccine recommended for pregnant women “doesn’t actually prevent [whooping cough]” and “makes you an asymptomatic carrier putting newborns more at risk”.

As we will explain below, this post uses flawed reasoning to support the narrative that the Tdap vaccine creates silent carriers of whooping cough. Further, as Science Feedback has explained in numerous previous claim reviews, vaccines are generally safe and reduce the risk of serious illness and death, including for whooping cough.

The Tdap vaccine helps protect babies from contracting whooping cough

Whooping cough can cause serious illness in people of all ages. However, babies are among those at highest risk for complications or death from the disease. This is in part because babies can’t receive their first dose of the DTaP vaccine, which protects against whooping cough, until they’re two months old.

According to the U.S. Centers for Disease Control and Prevention (CDC), “[a]bout one third of babies younger than 1 year old who get whooping cough need care in the hospital, and 1 out of 100 babies who get treatment in the hospital die”.

Health agencies including the CDC and the World Health Organization (WHO) recommend that pregnant women receive a Tdap booster in their third trimester to provide protection against whooping cough for their babies. This booster helps pregnant women pass immunity to their babies through the placenta, and provides protection during the vulnerable period between birth and when a newborn can receive their first dose of DTaP vaccine.

This recommendation is supported by numerous studies which have consistently found a reduced incidence of whooping cough among infants whose mothers received a Tdap booster^[1,2,3].

One systematic review from Vygen-Bonnet et al. evaluated both the safety and effectiveness of pertussis vaccination during pregnancy. Regarding effectiveness, they found that among more than 850,000 mother-infant pairs across eight studies, there was a reduction in pertussis infection, hospitalization, and death in infants from zero to three months of age^[1].

Another retrospective study of nearly 150,000 infants found that maternal Tdap vaccination during pregnancy reduced the risk of pertussis in newborns under two months of age by 91%^[3].

And a retrospective case-control study comparing pregnant women who received a Tdap vaccine during the third trimester to those who didn’t found that the “overall effectiveness of vaccination”—defined as a lack of laboratory-confirmed illness in a newborn—was 78%^[4]. It additionally found a higher level of effectiveness for preventing pertussis hospitalization among infants whose mothers received Tdap vaccination:

“Approximately 65.4% […] of case-infants were hospitalized during the course of their pertussis infection. When we examined the effectiveness of Tdap at preventing infant pertussis hospitalizations, the VE point estimate for vaccination during the third trimester increased to 90.5%.”

Infectious diseases can spread easily during their incubation period, unrelated to whether or not a person is vaccinated

The post uses flawed reasoning to support the claim that people vaccinated against whooping cough present as “asymptomatic”, which “put[s] newborns more at risk” of the disease. It operates on the assumption that unvaccinated people present more evident symptoms of whooping cough, and are therefore easier to avoid for the duration of illness.

In reality, unvaccinated people may not know they have whooping cough since the disease can present with mild symptoms that mirror the common cold during its incubation period. People can also be asymptomatic during this incubation period, which typically lasts for one to two weeks.

As shown in Figure 1 below, whooping cough eventually progresses into a later stage of symptoms for which the disease gets its name. This can include intense coughing fits followed by a “whooping” sound.

However, according to the CDC, “the ‘whoop’ is often not there for people who have a milder illness”, such as adults and teenagers, who are less likely to become severely ill from the disease. It’s possible a person infected with whooping cough may never present with the “whooping” symptom, but regardless of this, they’re still capable of passing the disease on to others who are more vulnerable to it.

Figure 1 – Progression of whooping cough and description of symptoms at various stages of infection. Source: CDC.

Moreover, unvaccinated people pose a greater transmission risk of infectious diseases, regardless of whether or not they show symptoms of the disease. According to the CDC, “a vaccinated person is far less likely to die or become seriously ill than someone whose immune system is unprepared to fight an infection”.

This includes transmission risk of whooping cough. The “infection is usually not as bad for people who have gotten vaccinated […] but still get sick”, in part because the length and intensity of whooping cough symptoms are usually less severe in vaccinated people.

Conclusion

Evidence shows that pregnant women who receive a Tdap booster during their third trimester of pregnancy can reduce the risk of whooping cough for infants during the vulnerable period before their first DTaP vaccination. While the DTaP and Tdap vaccines don’t provide perfect, lifelong immunity from whooping cough, they do reduce the risk of serious illness, long-term health complications, and death from the disease.

REFERENCES

• 1 – Vygen-Bonnet et al. (2020) Safety and effectiveness of acellular pertussis vaccination during pregnancy: a systematic review. BMC Infectious Diseases.
• 2 – Skoff et al. (2023) US Infant Pertussis Incidence Trends Before and After Implementation of the Maternal Tetanus, Diphtheria, and Pertussis Vaccine. JAMA Pediatrics.
• 3 – Baxter et al. (2017) Effectiveness of Vaccination During Pregnancy to Prevent Infant Pertussis. Pediatrics.
• 4 – Skoff et al. (2017) Impact of the US Maternal Tetanus, Diphtheria, and Acellular Pertussis Vaccination Program on Preventing Pertussis in Infants <2 Months of Age: A Case-Control Evaluation. Clinical Infectious Diseases.