A recent article published in Vaccines summarizes the data presented and the meeting discussions regarding pertussis vaccination in pregnancy (ViP). The article also presents a review of the literature on this subject.
Despite the availability of acellular (Ap) and whole-cell (wP) pertussis vaccines, Bordetella pertussis – the causative agent of whooping cough, still seriously affects newborns and young children, causing considerable morbidity and mortality.
Vaccination of pregnant women against B. pertussis is recommended (in 2011) to prevent the susceptibility of newborns and infants to infection. Evidence suggests that vaccination against B. pertussis during pregnancy is safe for both mother and fetus.
The antibodies against B. pertussis produced in the mother after vaccination is transferred through the placenta. Antibodies also confer protection to the young child through breast milk. The effectiveness of vaccination is evidenced by the reduction in the incidence of a severe form of pertussis in young children within a short period of time after the implementation of the vaccination strategy.
In 2021 (November 30 to December 1), an expert meeting was hosted virtually by the Global Pertussis Initiative (GPI). A total of 30 pertussis experts from 18 countries gathered around the world to discuss pertussis vaccination in pregnant women.
Experts have discussed that although the immune system undergoes many modulations after pregnancy, the pertussis vaccine-induced immune response is almost similar in pregnant and non-pregnant women. It was also found that the immune response induced by vaccination is not affected by the state of pregnancy.
Immunoglobulin G (IgG) is the main antibody that crosses the placenta. Its concentration increases gradually in infants and during childbirth. Eventually, the infant has a higher IgG concentration than the mother. Transplacental transfer of immunoglobulin into the bloodstream of the fetus occurs via newborn Fc receptors (FcRn). While IgG transfer is different in different IgG subclasses; vis, IgG1>IgG3=IgG4>IgG2 (according to studies).
Vaccination against B. pertussis induces IgG3 and IgG1 subclasses, which efficiently cross the transplacental barrier. The efficiency of IgG transfer across the placenta also differs depending on immunoglobulin function.
It has been found that antibodies against B. pertussis increase one month after vaccination, after which there is a rapid decline – during the first year after childbirth. Therefore, vaccination of all pregnant women was recommended.
Although there is some debate about the optimal timing of pertussis vaccination in pregnant women, several studies have indicated that vaccinating pregnant women against B. pertussis early in the third trimester results in higher antibody concentrations than vaccination at the end of the third trimester.
A recent meta-analysis found no association between the timing of the Tdap (tetanus-diphtheria-acicular pertussis) vaccine given during pregnancy and subsequent immune response in the infant. Because pertussis vaccine is given with TT and DT, there may be a change in the infant’s immune system response to vaccines containing TT and DT.
Researchers found that the concentration of anti-DT IgG antibodies after the series of primary vaccinations – before and after the booster dose of the DT-containing vaccine – was significantly lower in infants of vaccinated mothers than in those whose mothers were not vaccinated. In addition, vaccination of pregnant women resulted in an increased anti-DT antibody response in infants.
Vaccination of the mother against B. pertussis during pregnancy appeared to alter immune responses in infants. It was also noted that the antibody concentrations against B. pertussis were lower after the primary dose and the booster dose in infants born to vaccinated mothers than in those born to unvaccinated mothers. In addition, premature infants were more vulnerable to infection risk in infancy and had lower pertussis antibody concentrations. B. pertussis post-vaccination.
Evidence suggests that vaccination against B. pertussis during pregnancy induces antibodies against pertussis in breast milk. Immunoglobulins A and G have been detected in breast milk and colostrum of women vaccinated during pregnancy during the first eight weeks after delivery at term.
Additionally, recent studies report that IgG and IgA concentrations were similar in colostrum and breast milk after preterm and term delivery, and that antibodies were present up to 12 weeks postpartum. However, the data on this subject seem insufficient; therefore, further studies are needed to understand the effects of vaccinating pregnant women on neonatal and fetal immune systems.
In addition, wP vaccines are mainly used in middle and low income countries. Lower antibody concentrations were observed in infants born to mothers vaccinated after a series of wP vaccines, compared to infants vaccinated with aP and born to mothers who received a P vaccine during pregnancy. However, antibody functionality was higher in those who received the wP vaccine. Further studies are warranted, particularly in low-income countries, where data are sparse – likely due to difficulties in monitoring vaccines.
It should be noted that during the period of coronavirus disease 2019 (COVID-19), infants reported a decrease in pertussis infection. It is therefore necessary to continue enhanced observation of pertussis infection in the era of COVID-19.
The need for vaccination against B. pertussis during pregnancy should also be recommended, as reports suggest that the number of vaccinations has been lower during the pandemic.