Pertussis

What is Pertussis?

Pertussis (whooping cough), is an acute respiratory illness caused by the Bordetella pertussis bacterium.

Symptoms include:

  • Prolonged cough lasting 1–2 months or longer
  • posttussive vomiting
  • repeated violent coughs
  • high-pitched inspiratory whoop

Note: Infants less than 6 months old, adolescents and adults often have fewer classical symptoms without paroxysms or whoop.1

Pertussis is preventable by vaccine and the vaccine is an acellular pertussis-containing vaccine, available only in combination with diphtheria and tetanus in Australia. It was introduced into Australia’s mass immunization programs in 1954 and subsequently the Immunize Australia Program in 1993 to increase childhood vaccination rates. Pertussis vaccine coverage has increase dramatically over the years, with fewer deaths associated with the 2008-2012 national epidemic compared to the late 1990s epidemic despite much higher number of cases.1

Newborn immunisation

Pertussis vaccine is currently recommended in a 5-dose schedule as per following: 2, 3

  • 6-8 weeks, 4 and 6 months: DTPa-hepB-IPV-Hib (diphtheria-tetanus-acellular pertussis, hepatitis B, inactivated poliovirus, Haemophilus influenzae type b)
  • 18 months: DTPa
  • 4 years old: DTPa-IPV

The 1st dose significantly reduces the incidence of severe pertussis disease in young infants4-7 and protection increases further with the doses given at 4 and 6 months of age, as measured by hospitalization rates and mortality. Doses of pertussis-containing vaccine at 18 months and 4 years of age are needed because pertussis immunity wanes after receiving the infant doses.8 ,9 Moreover, preschool and school-aged children are also an important source of infection for infants.

3rd trimester vaccination

DTPa vaccine is recommended as a single dose in each pregnancy. The optimal time for vaccination is between 28 and 32 weeks gestation (i.e. early 3rd trimester) because maternal antibodies are actively transported to the fetus 30 weeks gestation onwards.11 The interval between maternal vaccination and delivery should be at least 4 weeks.11 Vaccination during pregnancy reduces the risk of pertussis in pregnant women and their newborn due to direct passive protection of pertussis antibodies from the mother to fetus during pregnancy.11, 12In a landmark study, vaccination of mothers at least 7 days before delivery reduced pertussis disease by 91% in infants <3 months of age.13

Waning immunity

Pertussis was the most common vaccine preventable disease with 34,793 notifications in 2010.14 Despite a longstanding pertussis immunization program, and a substantial decline in morbidity and mortality from the disease, pertussis remains highly prevalent in Australia, with epidemics occurring every 3–4 years.15 Despite high vaccine coverage in young children,  there has been a stepwise increase in pertussis notification rates over the past few years, both nationally & in WA, (Figure 1), with most of disease observed in older children and adults. This is majorly due to waning vaccine-induced immunity, better disease awareness, greater availability of more sensitive PCR diagnostic tests, improved reporting and surveillance, and organism mutation Household contacts (especially parents), carers and general public are the infection sources in more than 50% of cases.15

Figure 1: Pertussis notification rates for Western Australia and Australia, 1991–2011

Future of pertussis vaccines

A vaccine that effectively reduces transmission and disease is an important objective for herd immunity. In this regard, research on live attenuated vaccines, and the potential for acellular vaccines with improved adjuvants and less reactogenic whole-cell vaccines are currently underway.16 3rd trimester immunization will prevent early infant mortality and morbidity, while the 18-month booster under the NIP will improve control in early childhood and finally, having a pertussis booster during adulthood will maintain herd immunity.

 References

  1. Australian Government. In: Vaccine Preventable Diseases in Australia, 2005-2007. Issue Supplement 2010. Canberra: Australian Goverment Department of Health & Ageing
  2. Australian Technical Advisory Group on Immunization. Australian Immunization Handbook Australian Government Department of Health; 2018
  3. Tiwari TS, Baughman AL, Clark TA. First pertussis vaccine dose and prevention of infant mortality. Pediatrics 2015;135:990-9
  4. Tanaka M, Vitek CR, Pascual FB, et al. Trends in pertussis among infants in the United States, 1980–1999. JAMA 2003;290:2968-75.
  5. Tiwari TS, Baughman AL, Clark TA. First pertussis vaccine dose and prevention of infant mortality. Pediatrics 2015;135:990-9
  6. Foxwell AR, McIntyre P, Quinn H, Roper K, Clements MS. Severe pertussis in infants: estimated impact of first vaccine dose at 6 versus 8 weeks in Australia. Pediatric Infectious Disease Journal 2011;30:161-3.
  7. Shinall MC, Jr., Peters TR, Zhu Y, Chen Q, Poehling KA. Potential impact of acceleration of the pertussis vaccine primary series for infants. Pediatrics 2008;122:1021-6.
  8. Quinn HE, Snelling TL, Macartney KK, McIntyre PB. Duration of protection after first dose of acellular pertussis vaccine in infants. Pediatrics 2014;133:e513-9.
  9. Eberhardt CS, Blanchard-Rohner G, Lemaître B, et al. Maternal immunization earlier in pregnancy maximizes antibody transfer and expected infant seropositivity against pertussis. Clinical Infectious Diseases 2016;62:829-36.
  10. Quinn HE, McIntyre PB. Pertussis epidemiology in Australia over the decade 1995–2005 – trends by region and age group. Communicable Diseases Intelligence 2007;31:205-15.
  11. Eberhardt CS, Blanchard-Rohner G, Lemaître B, et al. Maternal immunization earlier in pregnancy maximizes antibody transfer and expected infant seropositivity against pertussis. Clinical Infectious Diseases 2016;62:829-36
  12. In: Pertussis Vaccines for Australians: Information for immunization providers 2016. Canberra NCIRS.
  13. Amirthalingam G, Andrews N, Campbell H, et al. Effectiveness of maternal pertussis vaccination in England: an observational study. The Lancet 2014;384:1521-8.
  14. Australian Bureau of Statistics. In: Communicable Diseases 2015. Canberra ABS.
  15. In: Pertussis Vaccines for Australians: Information for immunisation providers 2016. Canberra NCIRS.
  16. Thorstensson R, Trollfors B, Al-Tawil N, et al. A phase I clinical study of a live attenuated Bordetella pertussis vaccine — BPZE1; a single centre, double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally to healthy adult male volunteers. PLOS ONE 2014; 9: e83449.