Abstract
Pertussis deaths occur primarily among infants who have not been fully immunised. In Ontario, Canada, an adult booster dose was recently added to the publicly funded immunisation programme. We applied number-needed-to-treat analyses to estimate the number of adults that would need to be vaccinated (NNV) to prevent pertussis disease, hospitalisation and death among infants if a cocoon strategy were implemented. NNV=1/(P(M) X R) + 1/(P(F) X R), where P(M),P(F) (proportion of infants infected by mothers, fathers) were sourced from several studies. Rates of disease, hospitalisation or death (R) were derived from Ontario's reportable disease data and Discharge Abstract Database. After adjusting for under-reporting, the NNV to prevent one case, hospitalisation or death from pertussis was between 500-6,400, 12,000-63,000 and 1.1-12.8 million, respectively. Without adjustment, NNV increased to 5,000-60,000, 55,000-297,000 and 2.5-30.2 million, respectively. Rarer outcomes were associated with higher NNV. These analyses demonstrate the relative inefficiency of a cocoon strategy in Ontario, which has a well-established universal immunisation programme with relatively high coverage and low disease incidence. Other jurisdictions considering a cocoon programme should consider their local epidemiology.
Highlights
Pertussis is an infectious respiratory disease caused by Bordetella pertussis, typically presenting with a paroxysmal cough followed by a characteristic ‘whoop’ sound
Between 2005 and 2009, 844 confirmed cases of pertussis among infants less than one year old were reported through integrated Public Health Information System (iPHIS) in Ontario
NNV estimates for a range of each outcome of disease, hospitalisation and death are provided in Tables 2, 3 and 4, respectively
Summary
Pertussis is an infectious respiratory disease caused by Bordetella pertussis, typically presenting with a paroxysmal cough followed by a characteristic ‘whoop’ sound. Adolescents and adults are less likely to present with typical symptoms, which leads to under-diagnosis by physicians, who may fail to consider the diagnosis [1]. Diphtheria and tetanus toxoids, acellular pertussis, inactivated poliomyelitis and Haemophilus influenzae type b (DTaP-IPV-Hib) is administered as a primary series at 2, 4 and 6 months with a booster dose at 18 months of age. Since 2003, an adolescent acellular pertussis booster dose using the adolescent/adult formulation (Tdap) has been offered at 14–16 years, with coverage among 17-year olds estimated at 67.7% [5]. On 8 August 2011, a single dose of Tdap vaccine (Adacel by Sanofi Pasteur or Boostrix by GlaxoSmithKline) was publicly funded for adults aged 19 to 64 years who had not previously received an adolescent booster
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