Vaccination rates in Australia have fallen below the herd immunity threshold, here’s what you need to know…

By mid-April this year, Australia had already recorded 59 measles cases – more than the 50 cases recorded in the entire previous year – with most cases currently concentrated in Victoria, New South Wales and Western Australia.

While Australia was certified as no longer measles-endemic in 2014, meaning there is no circulating measles virus in the community, there has been a resurgence overseas, posing a risk for travellers – and people who are in contact with those travellers when they return, explains Professor Nigel Crawford, Medical Head of Immunisation Services at the Royal Children’s Hospital Melbourne.

What’s behind the uptick in cases?

Indonesia (including Bali), Thailand, Vietnam, Malaysia, the Philippines are all reporting high case numbers, and the United States has seen over 800 cases and their first measles death in over a decade.

Unsurprisingly, most cases are either directly imported from international travellers or are contacts of these travellers.

All cases are rigorously tracked through public health units to prevent community circulation, which is particularly crucial given that one person with measles typically infects 13 to 18 people.

The increase in cases also comes at a time when vaccination rates have declined slightly to around 91 – 92% MMR coverage in childhood – which is below the 95% target to get herd immunity, underscoring the importance of encouraging patients to ensure they are protected.

Clinical presentation

The classic presentation of measles begins with a prodromal phase lasting 2-4 days, which can resemble other viral illnesses with fever, malaise, cough, and notably, conjunctivitis. The presence of conjunctivitis should raise clinical suspicion.

Following the prodromal phase, a characteristic maculopapular rash develops, beginning on the face and neck before spreading downward to the trunk. Unlike many other viral rashes, it is typically not itchy.

The rash may appear different on various skin tones, so clinicians should familiarise themselves with these variations.

An important diagnostic feature is Koplik spots – small white spots inside the cheeks that appear early in the course of infection. Examining the oral cavity for these spots can help confirm the diagnosis.

Diagnosis

The primary diagnostic test for measles is a respiratory PCR (polymerase chain reaction) test. A nose and throat swab should be sent urgently to the local reference laboratory with a specific request to test for measles.

Serology is also useful, although results take longer. IgM positivity suggests acute infection, but this may not be immediately detectable, potentially requiring repeat testing.

PCR is considered the gold standard test, but if there is uncertainty about the diagnosis, collecting both a respiratory specimen and blood sample is recommended. The local public health unit can provide guidance on testing requirements.

Complications

Complications from measles can be serious and potentially fatal. These include:

• Otitis media (relatively common)
• Pneumonia (more common in children)
• Neurological complications including encephalitis (more common in adults)

A rare but uniformly fatal complication is subacute sclerosing panencephalitis (SSPE), which causes progressive, serious brain damage. This occurs in approximately 22 per 100,000 measles cases and typically presents weeks after the initial infection.

Vaccination

Measles vaccination in Australia uses the measles-mumps-rubella (MMR) vaccine, which contains live attenuated viruses. People may experience fever and rash 5-14 days post-vaccination, which indicates the vaccine is working.

Vaccine effectiveness

The MMR vaccine provides around 95% protection after the first dose. To catch the 5% of non-responders, a second dose is given, resulting in about 99% individual protection once the two-dose schedule is completed. In Australia, these doses are currently administered at 12 and 18 months of age. The vaccine given at 18 months is combined MMR-Varicella (MMR-V).

Who should and should not receive the vaccine?

People born before 1966 are generally assumed to have had natural measles infection or exposure, as the disease was endemic before widespread vaccination began in the late 1960s.

Those born from 1966 onwards should have received two doses of measles-containing vaccine.

For those with uncertain vaccination or infection history, there is no harm in receiving an additional MMR dose.

However, as a live attenuated vaccine, MMR is contraindicated in people with significant immunosuppression.

Post-exposure prophylaxis

Normal human immunoglobulin can provide post-exposure protection for immunocompromised people who cannot receive the MMR vaccine. This includes patients with cancer diagnoses or those on biologic therapies for autoimmune conditions.

Immunoglobulin should ideally be administered within 72 hours of exposure, though it can be given up to 6 days (144 hours) post-exposure. Access to immunoglobulin is coordinated through local public health units.

Special considerations for infants travelling overseas

Infants under six months of age typically have protection from maternal antibodies transferred during pregnancy. However, this protection wanes between 6-11 months, leaving the baby vulnerable before the scheduled first dose at 12 months.

For infants aged 6-11 months travelling to endemic countries, an additional “dose zero” of MMR is recommended. This is safe and provides good protection, but the child should still receive the standard doses at 12 and 18 months upon return.

For children over 11 months, an early dose can be administered before travel, which will count as a valid dose in the Australian Immunisation Register.

Precautions for suspected cases at your practice

The infection spreads through airborne droplets and respiratory secretions. Patients become contagious during the prodromal phase, before the characteristic rash appears. They remain infectious until about four days after the rash onset. Symptoms typically develop 7-18 days after exposure, which explains the 21-day monitoring window for returning travellers who may have been exposed.

While you obviously can’t prevent all transmission, there are some precautions you can take.

Initial triage and isolation

Ideally, patients with suspected measles should be triaged over the telephone and encouraged not to enter the waiting room or consulting room. Where possible, assess them outside or in the car park to minimise exposure to other patients, particularly those who are immunosuppressed.

If a patient with suspected measles does enter the practice, isolation measures should be implemented immediately:

• Ask the patient to wear a mask (acknowledging this may be difficult for young children)
• Use appropriate personal protective equipment
• Assess them for respiratory and neurological complications to determine whether they can be managed as an outpatient or require hospitalisation

If hospitalisation is necessary, notify the ambulance service and hospital about the suspected diagnosis to minimise potential exposure in the emergency department.

Environmental considerations

The measles virus can survive on surfaces for up to two hours. Practice rooms should be thoroughly cleaned after examining a suspected case, and it may be necessary to keep the room vacant for a period before using it again. Consider designating a specific room for examining patients with suspected infectious diseases.

Notifying cases and contact tracing

Measles is a nationally notifiable disease requiring the highest level of notification.
Contact tracing is primarily managed by local public health units, who identify close household contacts and locations the infected person has visited (such as shopping centres, flights, etc.). GPs can support this process by appropriately testing and managing patients who may have been exposed.

Key Messages

• There is no specific antiviral treatment for measles – management is supportive once infection occurs.
• Prevention through vaccination is crucial.
• Babies aged 6-11 months and adults aged 20-40 are particularly vulnerable groups.
• Younger children may develop severe disease, while adults aged 20-40 may have gaps in their vaccination history.
• When consulting with patients in this age range, especially those planning travel to endemic regions, verify their immunisation status and ensure they have received two doses of MMR.
• Have a high index of suspicion for people presenting with a rash within 21 days of return from travel to endemic regions, especially if their vaccination history is incomplete.

Resources

The Australian Immunisation Handbook

Melbourne Vaccine Education Centre

Better Health Channel (Victoria)

Chief Health Officer alerts (national and state-based)

Like this article? Check out the related podcast…

Infectious disease specialist Professor Nigel Crawford discusses the surge in measles cases and considerations in primary care.