The primary aim of this study was to assess parental attitudes towards, and awareness of, the funded parental pertussis vaccination program that was implemented by the Victorian Department of Health in 2009 as part of a cocooning strategy. Uptake of the vaccine by parents under this program was also estimated. Although the Victorian cocooning strategy for pertussis ended in 2012, the results of this study provide useful data that may be used to inform the implementation of similar programs in future. In particular, information on parents’ attitudes towards the use of parental vaccination as part of a cocooning strategy could be used to inform program materials for parents and to develop communication strategies for future programs. After adjustment for LGA populations, the proportion of mothers surveyed who received pertussis vaccine following the birth of their most recent child was 68%. For fathers, the proportion was 49%. These proportions were higher than expected given vaccine distribution records indicated that sufficient vaccine had only been distributed to cover 50% of new parents (Personal communication: Mr Michael Batchelor, Manager, Immunisation Section, Department of Health, 8 March 2010). It needs to be acknowledged that this finding may be indicative of the presence of selection bias in this study, with vaccinated parents possibly overrepresented in our sample. Of the parents who were not vaccinated, the most common reason given was a lack of awareness that a free vaccine was available. This suggests that additional funding to promote or advertise the vaccine to new parents may have resulted in greater uptake under the program implemented in 2009. In conducting these types of programs, funding allocated towards the development of a communications campaign aimed at promoting the program to parents, and considering incentives for hospitals, local councils, and general practitioners to inform and vaccinate their patients, may also assist with the uptake of vaccine.
In general, there was a high level of knowledge and awareness of pertussis as a childhood disease among parents in this study; 93% had heard of whooping cough or pertussis, 96% agreed or strongly agreed that pertussis could cause serious illness in infants, and 82% thought that infants were at risk of contracting pertussis. Although household contacts have been shown to be the most important source of infection for infants both in Australia [9, 10] and worldwide , not all parents were aware that adults could contract and transmit pertussis to their child. This lack of awareness has been identified internationally as a barrier to vaccination, along with limited understanding of the potential for pertussis to cause severe disease in infants [12, 13]. Consequently, educating parents of infants is an important step in removing barriers to vaccination; however, research has also shown that education alone is not sufficient to raise vaccination rates in parents .
The contrast between the numbers of parents residing in metropolitan areas who were vaccinated in hospitals compared with rural parents was striking. Only 6% of metropolitan mothers and 10% of metropolitan fathers were vaccinated in hospital, compared with 70% of rural mothers and 42% of rural fathers. The higher vaccine provision through rural hospitals could potentially be explained by differences in hospital policies between metropolitan and their (generally smaller) rural counterparts, particularly regarding the vaccination of fathers who would not be considered patients of the hospital. Maternity hospitals have been shown to be effective and timely providers of the pertussis vaccine to new parents, particularly amongst families of high risk infants such as neonates, with standing orders having been shown to successfully raise the vaccination rate to more than 80% of eligible women in the United States . Further education and incentives (financial or otherwise) for maternity hospitals may increase uptake of post-partum mothers, particularly in metropolitan areas.
Whilst only 21% of mothers and 23% of fathers agreed that the time and effort to be vaccinated was important in their consideration of vaccination, the results indicated that this, in fact, was a common barrier for parents, particularly for fathers. Interestingly, some parents who indicated that they were not vaccinated due to time pressures responded that, in general, it was of little or no importance in their decision-making process. This suggests that, despite good intentions, the reality of life once a child is born can mean that time and effort are indeed important barriers to vaccination. This disconnection between intentions to be vaccinated versus actually obtaining a vaccination suggests that positive attitudes towards vaccination do not necessarily predict behaviour. Lack of time was found to be a major reason for not being vaccinated in a previous study where, despite an education program that demonstrated a significant increase in knowledge and willingness to be vaccinated for pertussis, only 8% of participants were vaccinated .
The major limitation in this study was the response rate of 43% which reduced the power of the study, and may have introduced some bias. A post-hoc power calculation estimated study power at 41.2%. One likely reason for the low response rate was due to the fact that parents of young children have multiple competing demands on their time and thus have limited time to respond to surveys. It is unclear as to whether those that responded to the survey were more likely to be vaccinated or had greater knowledge of pertussis but this possibility has to be considered. Unfortunately due to time and resource constraints, only one reminder letter was sent to parents requesting their participation in this study. Additional contact from the researchers may have increased participation, which may have minimised responder bias. Despite this, the comparison with the most recent report available on births in Victoria in 2008  showed similar characteristics for maternal age, marital status and place of birth to the study respondents which provides some evidence for representativeness of the sample. There was a statistically significant difference between country of birth for mothers in this study compared to Victorian mothers in 2008. One possible explanation for this difference could be that the particular LGAs that were randomly selected for the survey differed in regards to mothers’ country of birth than when compared with the overall Victorian population. It is also possible that there was a difference in the return of the questionnaire based on mothers’ country of birth. There was insufficient information on non-responders to determine whether this has occurred.
A further limitation in this study was that participants were not asked when they were vaccinated relative to the birth of their child. As the questionnaire was administered approximately six months after the birth of their child, parents may not have been vaccinated in the initial two month period at which infants are most vulnerable prior to receiving their first dose of pertussis-containing vaccine at two months of age. Anecdotal information provided by parents in the comments section of the questionnaire indicated that some parents were vaccinated at the time of their child’s two month vaccinations. It is therefore possible that, among parents who were vaccinated at local councils or general practitioners, vaccination was received some time after their child’s birth: leaving their new baby vulnerable to infection, and thereby defeating the purpose of the program. Furthermore, the infant’s age at the time parents were surveyed may have impacted upon their responses to questions relating to their attitudes towards vaccination. It is plausible that a younger infant may be perceived by parents as more vulnerable to infection and hence a parent may be more supportive of vaccination. However, it is also plausible that the converse is true – an older infant might be considered more ‘robust’ to cope with a vaccination. The impact that the infant’s age had on parental attitudes towards vaccination was not able to be assessed.
It is also important to note that minor methodological differences between participating LGAs may have introduced some biases to the findings reported. Specifically, the study period was extended by one month in two rural LGAs in order to recruit sufficient study participants, although there was no change in the way the program was advertised or delivered during this time. Two potential participants in one rural shire were excluded due to incomplete names being provided by the LGA. One metropolitan LGA chose to post the questionnaires to participants directly, but unlike other LGAs, the introductory letters were not personalised and may account for a response rate of 30% for that LGA, which was the lowest response rate of participating metropolitan LGAs.
It is important to consider that the Victorian Government Department of Health initiated the free parental pertussis booster program in mid-2009 in response to the rising incidence of pertussis. The program ceased in Victoria on 30 June 2012 due to declining numbers of notified pertussis cases as well as limited evidence of the effectiveness of cocooning and doubts as to the cost effectiveness of the program. Similar cocooning programs introduced by other Australian jurisdictions, including South Australia, the Australian Capital Territory, Western Australia, and Queensland also ceased around the same time as Victoria, citing lack of evidence of effectiveness. A narrowed program targeting mothers in maternity hospitals continues in New South Wales . Results of a case control study examining vaccine effectiveness of a similar cocooning program in New South Wales indicated that maternal vaccination was associated with a lower risk of pertussis among unimmunised infants (unadjusted OR 0.49; 95% C.I. 0.32-0.76) . However, the study included mothers who had been vaccinated prior to the birth of their child, and as such, passive transfer of maternal antibodies may have contributed to the protective effect seen.
Although many countries around the world promote the cocooning strategy, the World Health Organization statement on pertussis vaccines states that “there is insufficient evidence to include this strategy in national immunisation programs” . Several submissions to the Australian Pharmaceutical Benefits Advisory Committee for the vaccine to be included on the National Immunisation Program for parents have been rejected . The Australian Government Department of Health and Ageing has since recommended that with the current absence of definitive evidence as to the effectiveness of the cocooning strategy at population level, practitioners should advise parents and other carers of infants less than six months of age to consider the potential benefits to themselves and their family of boosting their pertussis immunity, and that pertussis vaccine is available on prescription for parents and other carers who choose to receive it .