UKCAF website


Go to content

Main menu:


Zika and microcephaly

Documents > Science

Zika, Microcephaly and Guillain-Barré Syndrome:
Is mis-use of the 'Boostrix' vaccine the cause for the recent outbreak
of microcephaly amongst Brazilian infants?
Douglas Cross
20th February 2016

Amidst all the confusion and uncertainty on the cause of the rise in prevalence of microcephalic babies born in Brazil, stimulated by speculation over the possible role of the Zika virus, there is one change in public health policy in Brazil that seems to have gone unexamined.

To control the rising prevalence of Pertussis (whooping cough) the Brazilian government introduced a new mandatory programme of vaccination of all women between the ages of 12 and 39 with the Tdap vaccine (GSK's 'Boostrix'), starting in late December 2014.

A monitoring study of the vaccination of New Zealand women between 28 and 38 weeks into pregnancy with Tdap vaccine has reported that there were no adverse outcomes.(Walls et al) However, in a previous nationwide campaign in Brazil against rubella, the MMR vaccine was given post partum to mothers and infants without adverse outcomes . It was later found to have resulted in a small proportion of women being accidentally vaccinated during very early stages of a subsequent and unidentified pregnancy.(Soares et al).

The potential for accidental vaccination of some women in very early pregnancy with the Tdap vaccine in this new programme must therefore be acknowledged.

Cranial bone formation during the first trimester is subject to epigenetic regulation, and disruption of that process can result in malformation at full term. The first reports of a sudden rise in the prevalence of these microcephalic infants emerged in late summer 2015, while the first reports of Zika infection in Brazil came only in March 2015, possibly too late to cause cranial malformation. There would inevitably have been a short lag period before the increase in prevalence of microcephaly became evident.

The timing of the emergence of the new outbreak of microcephaly is therefore consistent with the initial implementation of the new Tdap vaccination programme in late 2014 and early 2015, had it resulted in disruption of cranial development in some fetuses during early 2015.

There is some debate as to the true scale of the reported increase in microcephaly in Brazil (Chee), and no clear evidence that this new public health policy initiative against Pertussis may be the cause of the current scare. However, whilst Zika infection is extensive in both Columbia and Venezuela, neither country has adopted the use of the Boostrix as a control strategy against Pertussis, as it is now used in Brazil.

Significantly, there are no reports of an increase in the birth rate of microcephalic infants in either of those countries. The Zika-induced rise in Guillain-Barré Syndrome in this region should be treated as an entirely separate epidemic, unrelated to the microcephaly outbreak. If mis-use of Boostrix is responsible for the recent sudden rise in microcephaly in Brazil, then stopping the programme immediately should result in the current epidemic of that condition disappearing by the end of the year., although it will have no effect on Zikainduced Guillain-Barré Syndrome.

The Thalidomide tragedy reminds us that any such potential link should be investigated as quickly as possible. If Zika is needlessly allowed to be blamed for the current panic, then fetuses will be needlessly aborted by women terrified by the confusion and uncertainty that is currently propagated by the health authorities and the media.


Douglas Cross

(Correspondence – doug@ukcaf.org)

Sources of information.

Walls T et al(2016) Infant outcomes after exposure to Tdap vaccine in pregnancy: an observational study.
BMJ Open 2016;6:e009536 doi:10.1136/bmjopen-2015-009536
Soares RC et al (2011)Follow-up Study of Unknowingly Pregnant Women Vaccinated Against Rubella in
Brazil, 2001–2002. J Infect Dis. (2011) 204 (suppl 2): S729-S736. doi: 10.1093/infdis/jir429
Chee Fu Yung (2016). Time for global action on Zika virus epidemic. BMJ 2016;352:i781


For a PDF version of this note, CLICK HERE


Back to content | Back to main menu