Health authorities across Australia are on high alert as measles cases rise across the country, fuelled by summer international travel and a decline in childhood vaccination rates.

Data from the National Centre for Immunisation Research and Surveillance (NCIRS) has found that for the first time in 10 years, Australia’s early childhood vaccination coverage has slipped below the critical 95% threshold required for herd immunity.

Nationally, coverage for two-year-olds has dropped to 89.7%, while as of late last year, the number of children receiving their first MMR (measles, mumps and rubella) dose on schedule had fallen by 11.4 percentage points compared to pre-pandemic levels.

In total, Australia recorded 168 measles cases in 2025 – a nearly threefold increase from the 57 cases seen in 2024.

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The decline in immunity has collided with a surge in measles infections from holiday travel. On Sunday, health departments in New South Wales and South Australia issued alerts after the national “Boxing Day cluster” grew to seven, believed to have been caused by a single traveller who was infectious while moving through several high-traffic public areas.

In South Australia, an adult who caught the virus abroad visited Westfield Marion and Event Cinemas on Boxing Day, followed by a visit to Cockles Cafe in Port Elliot on 28 December. The trail continued the following day when that person flew from Adelaide to Sydney on Qantas flight QF748, prompting health authorities in both states to trace fellow passengers and airport visitors.

NSW has now confirmed three cases within the last week, all involving travellers returning from south-east Asia. Beyond the recent flight, alerts are active for various locations across northern Sydney, as well as the Concord hospital’s emergency department on 3 January between 1pm and 4.10pm.

The Sydney locations are the Macquarie Centre on 27 December between 11.30am and 2.30pm, Waitara Family Medical Practice on 29 December from 9am to 10.30am, the food court and Kmart at Westfield Hornsby on 30 December between 12.30pm and 3pm, and the emergency department at Hornsby Ku-ring-gai hospital on 31 December between 5.15pm and 8pm.

The Boxing Day cluster has also reached Western Australia, where two cases – including one child – have been confirmed. Victoria has reported a separate case involving an adult who returned from Bali.

While the holiday cluster has prompted multi-state alerts, the rise began weeks earlier. Western Australia saw a steady rise in infections throughout December, reaching 60 cases for the year by late last month. Similarly, Queensland authorities issued warnings in mid-December after an infectious traveller arrived on the Gold Coast from Bali.

Because measles is airborne and can linger in a room for up to 30 minutes after an infectious person has left, authorities are urging all Australians to verify their vaccination status. Anyone born in or after 1966 who has not had two doses of the MMR vaccine is eligible for a free booster. Typical symptoms include a fever, cough, and runny nose, followed several days later by a distinctive red rash.