Whooping Cough vaccine in pregnancy 3rd trimester: does it work?

In recent years the Boostrix™ vaccine, protecting individuals against Diphtheria, Tetanus and Pertussis, has been recommended for all pregnant women in their third trimester. This has been in response to changing trends in the levels of pertussis (whooping cough) across Australia.

What is pertussis?

Pertussis, more commonly known as whooping cough, is a highly contagious bacterial infection of the lungs and airways caused by the bacteria Bordetella pertussis. It is known as whooping cough due to the distinctive noise that those who have the disease make when trying to take a breath after bouts of intense coughing. In its most severe form the disease can last for several months. This is why it is also sometimes referred to as the ‘hundred day cough’. Occasionally, whooping cough can be so severe that individuals with the disease are hospitalised. Inpatient treatment usually consists of making sure fluid intake is adequate, oxygen therapy and mechanical ventilation in the most severe cases. Hospital admissions for whooping cough are predominantly for children less than 6 months old with underlying conditions that complicate the illness such as cardiac, respiratory or neuromuscular disease (1).

Why is the vaccine now given before babies are born?

Neonates have historically been offered immunisation against pertussis at 2, 3 and 4 months of age as part of a combined vaccine that also protects against diphtheria, tetanus, polio, and Haemophilus influenza B (Hib). In recent decades, the changing epidemiology of pertussis has seen more mortality and morbidity in children under the age of two months who were not yet eligible for their vaccinations and were unprotected against the disease (2). As such, in response to the outbreak, many countries around the world have announced temporary pertussis vaccination programmes that are offered to women between the 28th and 32nd weeks of pregnancy to passively protect their unborn child from the disease.

Vaccine timing

There are two significant reasons why pertussis is given during pregnancy and not immediately after birth. Firstly, it has been evidenced that the immune system of newborns does not respond well to the pertussis vaccine immediately after birth (3). Secondly, vaccination does not result in immediate protection (4). There is clear evidence to suggest that babies born to women who received the vaccination at least a week before birth having a substantially reduced risk of becoming ill with whooping cough (5). Most expectant mothers will have already received the pertussis vaccine during their own childhood, but the additional vaccine boosts antibody levels and enables the transfer of a high level of antibodies across the placenta to protect the unborn child until they are due for their primary immunisation when aged two months (6).

Why is the optimal time for giving the vaccine between 28-34 weeks?

The specific times in which the vaccination is best given is based on the best available scientific evidence regarding how the immune system of both babies and mothers respond to pertussis immunisation:

• Antibody levels in adults have been shown to peak approximately two weeks after a pertussis booster, with a significant decline over the following months 
• Transplacental antibody transfer is minimal until week 34 of pregnancy
•  Levels of antibody transferred transplacentally may be sub-optimal if immunisation is given pre-pregnancy or early in pregnancy
• Immunisation given earlier than week 20 in pregnancy might also be falsely associated with unrelated adverse events identified at the routine 20 week anomaly antenatal scan

Immunisation is typically offered between 28-38 weeks, as it can ensure a greater overlap between the timeframe of maximal antibody levels and the timeframe of transplacental antibody transfer. The 28 week vaccination option will also provide some protection to babies that are born prematurely and may be particularly exposed to complications from pertussis as a result.  Initially the recommended vaccine was Repevax, although this has changed to Boostrix-IPV due to concerns over the long term availability of Repevax and its ability to ensure sufficient supplies were available for the programme. There are no safety concerns regarding the vaccine, which has been in widespread use as part of pre-school booster programmes across the world since the 1950s. Inactivated vaccines do not replicate, and therefore can cause no infection in either the mother or unborn child.

The new vaccination programme performance

There has been a significant reduction in pertussis incidence in all countries that have implemented the programme. A 2014 study, published in The Lancet, undertook an analysis of lab confirmed pertussis cases and hospital admissions for all infants between 2008 and 2013 and found that pertussis dropped significantly in this age group over the time period. Comparing data between 2012 and 2013, researchers discovered that pertussis incidence dropped from 328 to 72 cases, and hospital admissions fell from 440 to 150 over the same period of time (7).

As a result of the initial successes of the vaccination programme, most governing bodies in countries that have experienced pertussis epidemics have recommended its continuation for a minimum of a further five years. Combination dose vaccines will continue to be used, as there is currently no single pertussis vaccine available on the market.

References

1. Greenberg DP, von Konig CH, Heininger U (2005) Health burden of pertussis in infants and children Pediatr Infect Dis 24(5 Suppl)S39-43
2. Pillsbury A, Quinn HE, McIntyre PB (2014) Australian vaccine preventable disease epidemiological review series: pertussis, 2006-2012 Commun Dis Intell Q Rep 30:38(3):E179-94
3. Maltezou HC, Ftika L, Theodoridou M (2013) Nosocomial pertussis in neonatal units J Hosp Infect 85(4):243-8
4. Vermeulen F, Dirix V, Verscheure V et al (2013) Persistence at one year of age of antigen-induced cellular immune responses in preterm infants vaccinated against whooping cough: comparison of three different vaccines and effect of a booster dose Vaccine 31(15):1981-6
5. Campbell H, Amirthalingam G, Andrews N et al (2012) Accelerating control of pertussis in England and Wales Emerg Infect Dis 18(1):38-47
6. Esteves-Jaramillo A, Gomez Altamarino CM, Esparza Aquilar M et al (2012) Booster vaccination against Bordella pertussis during pregnancy Ginecol Obstet Mex 80(5):341-7
7. Amirthalingham G, Andrews N, Campbell H et al (2014) Effectiveness of maternal pertussis vaccination in England: an observational study Lancet 384(9953):1521-1528