The Australian Immunisation Handbook 10th Edition 2013

(see ‘Women who are planning pregnancy, pregnant or post-partum’ in 4.12.7
Recommendations above).
Recently, it has been recommended in the United States, the United Kingdom and
New Zealand that dTpa vaccine administered in the last trimester of pregnancy
be preferred to post-partum maternal immunisation, for various reasons,
including difficulties in implementation of the latter strategy, theoretical reasons
why vaccination during pregnancy might be more effective, and the favourable
safety profile of maternal vaccination. 53 Theoretical reasons for effectiveness are:
1) that administration of dTpa during the third trimester of pregnancy results in
high maternal pertussis antibody levels and transplacental transfer of antibodies
to the infant; 54,55 and 2) that the levels of pertussis antibodies measured in cord
blood in such infants are similar to those observed in infants at 12 months of age
following a 3-dose DTPa course. 56 This is likely to provide protection against
pertussis in the 1st month of an infant’s life, prior to commencement of the
primary DTPa schedule. In addition, a woman vaccinated with dTpa during
pregnancy will herself be protected against pertussis during the third trimester
and will be less likely to transmit pertussis to the infant after delivery. Although
specific safety data are limited, dTpa is an inactivated vaccine and there is
evidence for the safety of this and other inactivated vaccines, such as tetanus and
influenza, in pregnancy. 53,57 Safety of dTpa vaccines in pregnancy was not studied
specifically during pre-market evaluations, but review of the available data from
pregnancy registries, small studies and the United States Vaccine Adverse Event
Reporting System did not indicate a higher frequency or unusual pattern of
adverse events in pregnant women who received dTpa. 53
A potential disadvantage of giving dTpa in the third trimester of pregnancy
is that maternal pertussis antibodies may interfere with an infant’s immune
response following the primary 3-dose DTPa course at 2, 4 and 6 months of age, 53
a phenomenon referred to as ‘blunting’. 27,53,58 However, because correlates of
protection are not fully understood, the clinical importance of this is uncertain.
Although severe morbidity and mortality from pertussis is rare after 6 months of
age, it is possible that a reduced immune response to the infant’s primary course
of DTPa-containing vaccine could result in less protection against pertussis in the
2nd year of life. This provides the rationale for provision of an additional booster
dose of a pertussis-containing vaccine (DTPa) in the 2nd year of life to children
born to mothers who received dTpa during pregnancy (see ‘Infants and children’
in 4.12.7 Recommendations above).
Refer to 3.3 Groups with special vaccination requirements, Table 3.3.1
Recommendations for vaccination in pregnancy for more information.
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4.12 PERTUSSIS