Measles:
Vigilance after elimination

Why think of measles now?

Measles is caused by a paramyxovirus and remains one of the most contagious human infections, with a basic reproduction number (R₀) of 12–18. A single case in a susceptible population can rapidly lead to multiple secondary infections.

Table 1: Relative contagiousness of common infectious diseases (R₀).

The overlap between early measles symptoms and common winter respiratory illnesses creates a significant diagnostic challenge. The initial prodrome of fever, cough, coryza and conjunctivitis can be indistinguishable from influenza, RSV, adenovirus and other viral respiratory infections. This issue has become more important because the global epidemiology of measles has changed since the COVID-19 pandemic. Interruptions to routine childhood immunisation and catch-up vaccination programs during the pandemic led to a marked fall in global vaccine coverage. Large outbreaks have since occurred in Europe, Southeast Asia and parts of North America. Most Australian cases remain linked to overseas travel or contact with a returned traveller.

Measles vaccine was introduced in Australia in 1968, and widespread vaccination has dramatically reduced the incidence of disease. In 2014, the World Health Organization declared Australia free of endemic measles transmission. However, imported cases have continued to occur, and over the last year there have been several episodes of onward community transmission involving both vaccinated and unvaccinated individuals.

Figure 1: Annual notified measles cases by state and territory, Australia (past 10 years).

National Communicable Diseases Surveillance Dashboard, Assessed 10 June 2026.

What does measles look like?

Following exposure, measles typically develops after an incubation period of 10–14 days, although the range may be as short as 7 days or as long as 23 days. Illness begins with a prodromal phase lasting 2–4 days. During this period, patients usually develop a fever together with one or more of the classic “three Cs”: cough, coryza and conjunctivitis. There may also be atypical presentations with gastrointestinal symptoms.

Koplik spots are highly characteristic of measles and, when present, are considered pathognomonic. These are small bluish-white or white lesions on the buccal mucosa. They typically appear 1–2 days before the rash. However, they are not always seen, particularly if patients present late.

The characteristic measles rash is an erythematous maculopapular eruption that generally appears a few days after the onset of fever. The rash usually begins on the face before spreading downwards to involve the trunk, arms and legs. As the rash progresses, it may become confluent, particularly over the face and upper body.

Community transmission: why early detection matters

Measles is so contagious that even brief exposure can be sufficient for transmission. Recent Australian outbreaks have demonstrated that imported cases can rapidly lead to local transmission, particularly when diagnosis is delayed. Early recognition, immediate isolation and prompt notification to Public Health remain critical.

Although measles most commonly occurs in unvaccinated individuals, infection can occasionally occur in people who have previously received measles-containing vaccine, including those who have had two documented doses. These “breakthrough” cases may occur due to either primary or secondary vaccine failure. A single dose of a measles-containing vaccine is more than 95% effective, while two doses provide up to 99% protection against measles.

Primary vaccine failure is rare. Primary vaccine failure may occur due to failure to produce any humoral response to viral antigen (non-seroconversion) or problems with vaccine storage, cold-chain maintenance or administration. Patients with primary vaccine failure generally present with typical measles, including fever, cough, coryza, conjunctivitis and a classic rash.

Secondary vaccine failure occurs when a patient initially develops immunity after vaccination, but protection declines over time as antibody levels wane. Measles occurring in this setting is often termed “modified measles syndrome”. Some patients may present only with a febrile rash illness or mild respiratory symptoms. As a result, modified measles can easily be overlooked during influenza season. Patients with secondary vaccine failure generally have lower viral loads and are less infectious than unvaccinated patients with measles; however, transmission can still occur, and these cases remain important to identify.

Which patients should be tested?

Clinicians should maintain a low threshold for testing in patients with a compatible illness and relevant epidemiological risk factors. Testing should be strongy considered in patients with fever and a descending maculopapular rash, particularly when accompanied by cough, coryza or conjunctivitis, especially in the context of the following risk factors:

• Recent overseas travel, particularly to areas with known outbreaks or endemic transmission
• Contact with a suspected or confirmed measles case
• Infants too young to be vaccinated

Clinicians should also remember that measles does not always present classically. Increasingly, Australian cases are being recognised in partially immune individuals, who may present with mild or atypical symptoms.

An important point to note is that after receiving a measles-containing vaccine, people may develop a fever lasting two to three days, with associated malaise and a mild, non-infectious rash. The fever usually develops 7–10 days after vaccination (typically within 5–12 days). Approximately 15% of young children who receive the MMR vaccine experience a high fever (>39.4°C). Laboratory testing can distinguish wild-type (circulating infectious) measles from non-wild-type (vaccine strain) virus.

Respiratory Multiplex PCR Testing at Clinical Labs

Visit our Respiratory Testing pages for state-specific ordering instructions.

If you enjoyed this article, subscribe to our electronic Pathology Focus newsletter.

Subscribe Today!