Australia is in the grips of its worst whooping cough outbreak since the introduction of vaccines as people continue to fall behind on immunisations.
More than 41,000 cases of the highly infectious and deadly lung disease have been recorded in the nation so far this year, surpassing the previous annual record of 38,748 in 2011, according to an Immunisation Foundation of Australia report card.
About 130 people a day are diagnosed with whooping cough and, with 53 days left in 2024, figures are expected to surpass 45,000.
Whooping cough, also known as pertussis or the 100-day cough, is a bacterial infection that impacts the airways, causing uncontrollable coughing and difficulty breathing.
Symptoms can take up to two weeks to appear, allowing the bacteria to spread, and an infected person can remain contagious for three weeks if left untreated.
One person could spread the disease to up to 17 unvaccinated people, the European Centre for Disease Prevention and Control has found.
NSW and Queensland are the hardest hit, with each state accounting for about 30 per cent of cases, according to the foundation's findings.
School-aged children are among the most impacted, with those aged 10 to 14 accounting for 37 per cent of all diagnoses.
Victoria's Chief Health Officer Clare Looker issued a health alert in September after pertussis cases spiked tenfold compared to 2023, with nine- to 12-year-olds accounting for almost 40 per cent of cases.
"The increasing number of pertussis infections seen in Victoria is a public health concern, as it has led to an increase in cases amongst the most vulnerable population - infants under the age of six months," Dr Looker said.
Only one-in-five people aged over 50 are up to date with their whooping cough boosters. (Lukas Coch/AAP PHOTOS)
Whooping cough epidemics are fairly predictable as they follow a pattern, the head of the Molecular Medical Microbiology Lab at the University of Technology Sydney Laurence Luu said.
"However, we had not anticipated the magnitude of this outbreak, the largest since national notifiable disease reporting began," he said.
Dr Luu said a drop in vaccinations was behind the infection surge, and it can "spread like wildfire" as it is more contagious than the flu.
"While we do an incredible job protecting newborns and infants, re-vaccination or 'booster' rates are alarmingly low," he said.
One-in-four children turning 13 missed out on their whooping cough booster in 2023, and only one-in-five people aged over 50 are up to date with their vaccinations.
The Immunisation Foundation of Australia recommends adults get a booster shot at least every 10 years to maintain protection.
The ACT leads the nation in vaccination coverage among one-year-olds, with over 96.5 per cent, followed by Western NSW and Northern Sydney.
Areas with the lowest vaccination coverage include the Gold Coast, with 89 per cent, followed by the NSW north coast and Central Queensland region.
Australians should expect to see a surge in cases heading into the spring and summer months which are often associated with a spike in cases, with November usually the worst month.
Foundation founder Catherine Hughes, whose four-week-old son Riley died from whooping cough complications, said the disease remained a public threat in Australia and reiterated the importance of ongoing vaccinations.
"Many people are unaware of the necessity for a booster vaccine and are probably not adequately protected against whooping cough," she said.
"We all have a role to play in controlling the spread of whooping cough and reducing the risk of infection in ourselves and others."