Maternal Immunisation (‘Cocooning’) Before Pregnancy Halves Risk Of Whooping Cough In Infants Less Than 4 Months Of Age
The results of a study of the impact of a pertussis vaccine “cocooning” strategy for adults in New South Wales shows that a mother receiving the whooping cough vaccine before delivery lowers the risk of whooping cough (pertussis) infection in very young infants.
The research was carried out by Dr Helen Quinn, Professor Peter McIntyre, Dr Tom Snelling and colleagues at the National Centre for Immunisation Research and Surveillance for Vaccine Preventable Diseases, Sydney, based at the Kids Research Institute and the University of Sydney, New South Wales (NSW), Australia in collaboration with New South Wales Health and presented at this week’s Annual Scientific Meeting of the Australian Society for Infectious Diseases (ASID) in Canberra, Australia.
In 2009, NSW Health implemented an initiative for preventing whooping cough in young children by vaccinating the parents and other adult carers, termed a ‘cocooning’ strategy. The strategy was implemented primarily through general practice as well as maternity units as part of a public health response to a large pertussis epidemic that commenced in July 2008, and followed unfunded national recommendations for cocoon immunisation in place since 2003.
Cases in the study included NSW infants aged four months and younger diagnosed with laboratory-confirmed whooping cough during a two-year period 2009-2011. For each case, up to four controls were randomly sampled from a register of all NSW-born infants and matched to cases by date of birth and area of residence. Vaccination status of mothers was collected, in addition to other information including demographic data and vaccination status of other household members.
Data were available for 217 cases and 585 matched controls. Overall, 75% of cases and 77% of control mothers had received pertussis vaccine but only 47 (27%) of case mothers and 189 (41%) of control mothers were vaccinated at least 4 weeks before the index date, which was the onset of whooping cough in the case infant. Importantly, 14% of case mothers and 26% of control mothers were vaccinated before delivery, most within 2 years but up to 6 years previously.
Significant risk factors for infant pertussis included large households and less favourable socio-economic circumstances. After adjusting for other significant risk factors, vaccination of the mother before birth was significantly protective, with a reduction in whooping cough risk of almost 50%.
Although fathers and grandparents of cases were also less likely to have received timely vaccination, the study did not find any significant additional impact after accounting for maternal vaccination status. There was however protection from breast feeding in addition to maternal vaccination. Importantly, the siblings in case households were highly immunised, but significantly more likely than control households to be in age groups where immunity was likely to have waned (aged 2-3 years and 6 years and older).
Dr Quinn concludes: “Timely maternal vaccination was associated with a significant decrease in risk of pertussis prior to eligibility for the second infant dose at 4 months of age, with the greatest benefit found in infants of mothers who received vaccine before delivery. This is the first evidence of protection from maternal pertussis vaccination prior to the current pregnancy. It suggests that vaccination as part of pre-pregnancy planning would have the greatest impact on whooping cough infection.”
Key questions for local and international policy include whether vaccination should become a permanent part of the immunisation schedule or only be used in the context of an outbreak (as is currently the case in the United Kingdom).
Source: Australasian Society of Infectious Diseases