Babies develop fewer antibodies against pertussis (whooping cough) if the mother is given the pertussis vaccine before the 24th week of pregnancy. These findings are from a multi-year study carried out by RIVM among preterm and full-term babies and their mothers. The results show that transfer of antibodies from mother to child is less efficient before the 24th week compared to later in pregnancy. There are no indications that protection against pertussis is insufficient if the vaccine is given earlier, at around 22 weeks.
To protect their newborn baby against pertussis, pregnant women can get the DTaP vaccination from the 22nd week of pregnancy. This vaccine protects against diphtheria, tetanus and pertussis. After vaccination, the mother transfers the antibodies to the baby. This protects the baby against pertussis (whooping cough) throughout the first months of its life.
The study involved the collection of data relating to babies whose mothers received the DTaP vaccination between weeks 20 and 24 of pregnancy. This included babies carried to full term (approximately 40 weeks) as well as babies born prematurely. The results were compared with an earlier study among babies carried to full term whose mothers received the DTaP vaccination between weeks 30 and 33 of pregnancy.
Fewer antibodies if vaccination occurs before week 24
The study focused on the level of antibodies against pertussis in two-month-old babies. Babies carried to full term whose mothers received the vaccine between weeks 20 and 24 of pregnancy have around half the level of antibodies compared to babies carried to full term whose mothers received the vaccine between the weeks 30 and 33 of pregnancy.
Antibody levels in preterm babies whose mothers received the vaccine between weeks 20 and 24 of pregnancy were almost the same as antibody levels in babies carried to full term whose mothers received the vaccine between weeks 20 and 24 of pregnancy.
What does this say about protection?
The level of antibodies against pertussis that is required for sufficient protection is not known. It is likely that other factors besides antibodies play a part. In the UK, women can be vaccinated from the 16th week of pregnancy. British data show no difference in protection against pertussis between babies whose mothers were vaccinated earlier in the pregnancy and those whose mothers were vaccinated later. However, further study is needed to determine whether babies carried to full term and babies born prematurely benefit equally from vaccination earlier in the pregnancy.
For more information, read the article Maternal Pertussis Immunization and Immunoglobulin G Levels in Early- to Late-Term and Preterm Infants. JAMA Netw Open. 2024;7(7):e2424608.