There has been a stark rise in cases of pertussis – known as whooping cough –this year compared with the last two years, with 10,035 cases reported to health departments around Australia so far in 2024, after just 2,447 in the whole of 2023 and 482 in 2022.
Exacerbating the increase in cases are shortages of antibiotics.
So what is driving the rise, and how concerned should we be for those most vulnerable to it?
What is pertussis?
Pertussis is a highly contagious respiratory infection caused by a type of bacteria called Bordetella pertussis, and it spreads through droplets produced when coughing and sneezing.
Symptoms such as a mild fever, cough and running nose typically appear between one week and 10 days after infection, similar to cold and flu. But this can progress into a violent, rapid cough making it difficult to breathe, and attempts to inhale can produce a “whooping” sound, sometimes leading to vomiting and in rare cases seizures. Pneumonia is a common complication.
Babies younger than six months are most at risk of serious complications and death, and can catch the illness from adults who may be mildly affected and not even realise they have the disease.
Why are pertussis rates so high and is this unusual?
There have typically been epidemics of pertussis in Australia every three to four years. This normal cyclical pattern is due to waning immunity over time due to lack of exposure to circulating infection.
The last pertussis epidemic in Australia was eight years ago, in 2016.
The associate director of surveillance, coverage, evaluation and social science at the National Centre for Immunisation Research, Associate Prof Frank Beard, said while we would have expected a pertussis epidemic around 2020, the Covid-19 pandemic measures such as border closures, social distancing and masks resulted in a marked decrease of respiratory infections.
“It is no surprise to now see an increase in cases, given the length of time since the last pertussis epidemic,” Beard said.
Has there been a decline in vaccination against it?
Before the pandemic began, vaccination coverage of infants and children up to four years old was about 95%, and coverage of the adolescent booster dose, scheduled at 12 to 13 years, was about 87%.
“There were modest decreases in immunisation coverage due to the Covid-19 pandemic impacts, with pertussis immunisation coverage in young children decreasing by 1% to 2%,” Beard said.
“Data on pertussis immunisation coverage in pregnancy is not as readily available, however a review of coverage data by NCIRS and others showed that coverage in pregnancy between 2019 and 2021 in Australia was around 80% to 90%, which represents some of the highest pregnancy coverage figures globally.”
He said while overall pertussis vaccination rates were high in Australia by global standards, it was important to aim for as high a rate as possible.
Who should get vaccinated?
Babies receive their first vaccination at six weeks old (and again at four, six and 18 months and four years of age, for five doses total). Vaccinating pregnant women is critical, as their antibodies are passed on to the newborn, offering protection and reducing the risk of serious symptoms until newborns are old enough to be vaccinated.
Adolescents should receive a booster dose at about 12 to 13 years. Adults are recommended to receive a booster dose at age 65 if they have not had one in the past 10 years, as they are also more vulnerable to disease complications.
Healthcare workers, early childhood educators and carers are advised to receive a booster every 10 years.
Beard said adult household contacts and carers of infants aged less than six months should receive a booster at least two weeks before they have close contact with the infant if their last dose was more than 10 years ago.
Eligible people under 20 years old and refugees of any age can get a free catch-up vaccination through the national immunisation program.
National immunisation program vaccines are available through a range of health services including GPs, some local council immunisation clinics and community health centres, school vaccination programs, Aboriginal medical services and participating pharmacies.
What is being done about medicine shortages?
There is a national shortage of the liquid antibiotic known as azithromycin (brand name Zithromax), used to treat whooping cough and some other respiratory illnesses in young children.
A spokesperson for the Therapeutic Goods Administration (TGA) said the shortage is expected to continue until 29 November 2024, driven by increases in demand globally.
Clarithromycin powder (brand name Klacid) is an alternative treatment option but it is also in shortage until 31 August 2024.
The TGA has approved the temporary supply of an overseas-registered product, azithromycin powder, which contains the same quantity of the same active ingredient as Zithromax.
“We are also evaluating options for supply of further products,” the spokesperson said.