There has been a major resurgence of pertussis in Australia following the COVID-19 pandemic, with 57 257 cases (or 215 per 100 000) notified during 2024. Highest numbers were in 10–14-year-olds (20 286 cases) and 5–9-year-olds (12 645) followed by 15–19-year-olds (5008) and 0–4-year-olds (4732); however, cases have occurred in all age groups. The resurgence continued in 2025, when 25 272 (95 per 100 000) cases notified 1. Prior to the availability of pertussis vaccine, epidemics occurred every 3–5 years and in Australia were associated with a case fatality rate of 1%–3% 2, and 300–600 deaths 3, most of which were in infants. Mass infant pertussis vaccination with a three-dose schedule was introduced in the early 1940s with the aim of reducing circulation of Bordetella pertussis and burden of disease in infants. Infant deaths fell markedly but, despite many subsequent changes in the pertussis vaccination program with the addition of booster doses at 18 months, 4–5 years of age and in adolescence, pertussis transmission and regular epidemics have not been eliminated 3. Appreciation of continuing pertussis deaths in infants, albeit at a low level, led in 2015 to state-based funding and in 2018 to National Immunisation Program funding of a dose of diphtheria-tetanus-pertussis vaccine (dTpa) for all women in the 3rd trimester of pregnancy. The aims of this latest, effective strategy are to minimise the chance of the mother herself infecting the newborn and to provide the newborn with maternal antibodies before routine vaccination stimulates the infant's own protective immunity 4. During September 2024 we investigated a cluster of seven confirmed pertussis cases occurring over four weeks among members of three related, under-vaccinated households. Cases and contacts were investigated and managed by the Public Health Unit in collaboration with the treating doctors, in accordance with NSW pertussis control guidelines. Vaccination histories were obtained from the Australian Immunisation Register. Parents of the three families gave consent to publication of this report. We briefly describe the outbreak and the impact on it of vaccine hesitancy. Household A was first affected, with the index case a 6-week-old infant whose mother had declined maternal dTpa vaccination as she felt that health professionals had not provided the information she needed to decide in favour of vaccination. The infant developed worsening cough and apnoeic spells and required hospitalisation for nine days. We recommended testing of the preschool-aged sibling who had been coughing for two weeks, and pertussis was confirmed. This sibling had received NO vaccines and attended a form of care claiming exemption from section 18 of the Public Health Act 2010 (NSW) which requires children attending child care to be vaccinated. The preschool-aged sibling was the likely source of the infant's infection. In Household B the mother was the first to become infected and received azithromycin treatment to reduce her infectiousness. She had last received a pertussis-containing vaccine at 5 years of age and had declined maternal dTpa vaccination in two pregnancies due to an earlier miscarriage. Her newborn baby developed life-threatening pertussis with recurrent apnoea despite receiving two courses of prophylactic macrolide antibiotics as soon as being identified as the mother's contact. The newborn was hospitalised altogether for 14 days, including 10 days in intensive care (requiring mechanical ventilation for 6 days). It subsequently began a course of catch-up vaccinations. Two further cases occurred in this household despite receiving prophylactic macrolides: a vaccinated one-year-old and the father whose last pertussis booster was at 4 years of age. The mother was the likely source of the other three cases in Household B. Household C suffered a single case in an unvaccinated one-year-old. Our questioning revealed that the three households were related and had gathered for a family occasion when members of Household A were unknowingly infectious, leading to a pertussis cluster of seven cases of the 12 family members, with severe or life-threatening disease in two infants. We believe that this unusual situation was the result of the introduction of pertussis into Household A from an infected preschool-like facility exempt from the strict vaccination requirements of the Public Health Act 2010 (NSW) followed by intense spread between members of the three households. This spread likely occurred due to the waning of pertussis immunity among members who had missed adolescent and maternal boosters, and due to the complete lack of vaccination in some members. Furthermore, control of the spread was hindered by the delay in diagnosis and treatment of the first (source) case in Households A and B; these source cases only sought medical attention after an infant in their household was diagnosed with pertussis. It is also noteworthy that the newborn developed disease despite receiving appropriate prophylaxis with azithromycin then clarithromycin. We speculate that this occurred due to the intensity and prolonged duration of exposure of the newborn to its mother whilst she was unknowingly infectious. However, an alternate hypothesis is that the organism was resistant to macrolide antibiotics; B. pertussis resistance to azithromycin has only recently been identified in Sydney 5. Until improved vaccines are developed which stimulate durable mucosal immunity and thus reduce nasal B. pertussis colonisation, resulting in the elimination of regular epidemics, the primary goal of both routine pertussis vaccination and the case-based public health response is to prevent serious cases in young infants. Whilst the COVID-19 pandemic has been associated in Australia with a small decline in childhood vaccine coverage, mistrust and refusal of vaccines predated the pandemic 6, which was the situation in these households. Communicating messages about vaccination in a manner tailored to the needs of the audience and combating misinformation are essential elements in regaining the trust of the community 7. Maternal pertussis vaccination is safe 8 and effective in protecting infants to 8 months of age 4. Clinicians caring for pregnant women need to respond to each woman's desire for information, at the same time stating confidently that declining the offer of maternal pertussis vaccination entails a substantial risk to the infant, particularly in the midst of a large pertussis epidemic. The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
Ferson et al. (Sat,) studied this question.