One of the important hypotheses of vaccination is to make sure that all family members or others who may encounter a newborn child be vaccinated, especially since many vaccinations are not indicated for infants for a couple of months after birth–those newborns are very susceptible to vaccine preventable diseases until they themselves are vaccinated with the DTaP vaccine (which also protects against tetanus and diphtheria).
This protective “cocoon,” especially important with whooping cough (Bordetella pertussis), theoretically blocks the transmission of the disease to a newborn by creating a protective circle of vaccinated individuals around the newborn. A teenage sibling could catch the disease and accidentally infect the infant. Pertussis is bad enough for a teenager, but it can be deadly to a baby.
Even though the evidence for cocooning is growing, there are some flaws to the idea that are still being investigated in various parts of the world. One of the concerns is that asymptomatic carriers of pertussis (who have been vaccinated) might transmit the disease through a cocoon. However, scientists have known that the current version of pertussis vaccine, called acellular pertussis, isn’t as effective as it should be, but it is still better than not vaccinating. Much better. But that is a potential hole in the protective cocoon that needs to be understood better through research.
Without a doubt, vaccinating the pregnant mother against pertussis would be an important way to protect the future newborn baby, since the mother probably has more contact with the infant than any other individual in a household. But is it safe to give the Tdap vaccine (the adult version of the DTaP version) to a pregnant mother?
According to a recently published study in BMJ, the answer to that question would be an unqualified yes.
The study examined over 20,000 women who were immunized with the appropriate pertussis vaccine compared to a “matched” unvaccinated group (meaning that demographic and other factors between both groups were closely matched in selecting the unvaccinated group). The primary outcome examined, and for a pregnant woman, probably one of the most important, was stillbirth (intrauterine death after 24 weeks’ gestation).
Here are the key results:
- There was no evidence of an increased risk of stillbirth in the 14 days immediately after vaccination. In fact, there was a reduced risk (approximately 31% less) of still birth in mothers who were vaccinated, but statistically, that would be stretching the interpretation of the results way beyond reasonableness (even though if the numbers were still statistically weak, and showed an increased risk, the antivaccination cult would be trumpeting the numbers). Moreover, I cannot see a plausible mechanism where the vaccine would have a protective effect against stillbirth. But still, in such a large cohort, it’s comforting to know the risk is potentially lower.
- A similar result, that is, no evidence of increased risk of still birth, was observed later in pregnancy.
- There also was no evidence that the pertussis vaccination accelerated the time to delivery.
- Finally, the study found no evidence of an increased risk of stillbirth, maternal or neonatal death, pre-eclampsia or eclampsia, haemorrhage, fetal distress, uterine rupture, placenta or vasa praevia, caesarean delivery, low birth weight, or neonatal renal failure. All of these conditions are serious negative outcomes of pregnancy, and there was absolutely no higher risk of any of them after the pregnant women were vaccinated with the pertussis vaccine. None.
The statistical analyses were impressively sophisticated and appropriate for this type of epidemiological study. The researcher gained access to detailed medical records for all the participants, using a matched cohort analysis that adjusted for other risks for stillbirth, maternal and gestational age.
One of the interesting points I gained from reading this study is that there were 12 incidents of stillbirth soon after vaccination. Without any further information, that would sound scary, and would form the basis of anecdotal reports throughout the antivaccination community. Reports would be made to VAERS, memes would be published on Facebook, and certain people would be screaming about the vaccine. But this is where science comes in. The expected incidence of stillbirth for this group would be 15.8, which means that the stillbirth rate was substantially lower in the vaccinated group. The thing is stillbirths happen (sometimes as a result of preventable diseases like the flu).
The author, Katherine Donegan, who self-funded the study and received no monetary assistance from any corporation, wrote about the implications of her study:
Pertussis remains an important disease burden in young infants, and maternal immunisation is an important public health intervention to reduce this burden. The US already recommends maternal pertussis immunisation, although to date uptake has been low and the evidence of safety limited. This is the first large controlled study of the safety of maternal pertussis immunisation. With other countries considering similar interventions, and with the early results on efficacy also coming from the UK, our findings provide initial evidence for evaluating the safety of the vaccine in pregnancy for health professionals and the public and can help to inform vaccination policy making.
So, if you’re pregnant, protect your child from pertussis by getting vaccinated. It’s clearly safe. And it’s your best choice to protect you from accidentally transmitting pertussis to your newborn baby, a disease that is probably one of the most dangerous to a newborn. Vaccines really do save lives.
- Barlow RS, Reynolds LE, Cieslak PR, Sullivan AD. Vaccinated children and adolescents with pertussis infections experience reduced illness severity and duration, Oregon, 2010-2012. Clin Infect Dis. 2014 Jun;58(11):1523-9. doi: 10.1093/cid/ciu156. Epub 2014 Mar 14. PubMed PMID: 24633685.
- Donegan K, King B, Bryan P. Safety of pertussis vaccination in pregnant women in UK: observational study. BMJ. 2014 Jul 11;349:g4219. doi: 10.1136/bmj.g4219. PubMed PMID: 25015137.
- Mertsola J. Editorial commentary: pertussis is less severe in vaccinated than in unvaccinated patients. Clin Infect Dis. 2014 Jun;58(11):1530-2. doi: 10.1093/cid/ciu161. Epub 2014 Mar 14. PubMed PMID: 24633682.
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