A sharp rise in measles cases is being witnessed worldwide, with outbreaks occurring in almost every part of the world.
After decades of declining rates, it made a resurgence so strong in 2023, UK authorities were prompted to declare a national incident this January and the World Health Organisation (WHO) calling for an urgent response
Measles is the most contagious disease in the world according to the WHO and up until the introduction of a vaccine in 1963, caused deaths in the millions each year.
Global elimination efforts since have significantly helped reduce its spread, with an estimated 57 million deaths successfully prevented between 2000 and 2022.
But measles' high infectivity rate means even a select few countries with weak immunisation programs can pose a threat.
With Australia's high immunisation rates, do we really stand at risk of importing an epidemic?
Experts say while the likelihood of widespread transmission remains very low, with growing hesitancy to vaccines and lack of access, there are root problems to consider.
Cross-border transmission risks
Measles cases rose by almost 80 per cent worldwide last year compared to 2022.
More than 30,000 contractions were recorded in the WHO's European Region alone compared to just 941 the previous year, in what the organisation says was roughly a 40-fold increase.
In Australia, the infection rate remains well below pre-COVID levels but has seen a year-on-year increase since 2021, with most cases being overseas returns.
From no cases nationally that year, seven were recorded in 2022, 26 in 2023, and 40 in just six months this year, figures from the federal government's national notifiable disease surveillance system show.
Children under the age of five remain the most at-risk group of contracting measles, but anyone who hasn't developed immunity can be affected, including adolescents and adults.
Senior specialist adviser for Health Emergencies at Respond Global Chris Maher says child under-vaccination, which has worsened since the COVID-19 pandemic, remains the biggest driving force behind increasing infection rates.
"What happened during COVID was that vaccination programs tended to get disrupted all over the world and lots of kids missed their initial dose or their second dose. As a result, you've got a build-up of children who are susceptible," he told the ABC.
"With more and more non-immune kids we're getting more and more significant outbreaks.
"There is a constant need to keep people informed because everyone tends to get a bit blasé when there is no disease around. With so much international movement, there is a constant likelihood that diseases will be reintroduced."
Multifaceted drivers of under-vaccination
Australia's National Immunisation Program (NIP) provides free coverage of a range of communicable vaccine-preventable diseases, including measles, for young children.
The latest quarterly report of childhood immunisation coverage released in April showed 93.93 per cent of the national five-year-old cohort was fully immunised.
This rate, however, has seen a gradual decline in recent years, with a growing number of parents hesitant about having their children vaccinated.
"There are groups who are very low immunised and those are certainly at risk… communities where people are choosing not to vaccinate their kids," Mr Maher said.
Studies on under-vaccination have linked vaccine hesitancy and refusal, to the spread of vaccine-preventable diseases in the community.
Professor Margie Danchin, group leader of the vaccine uptake group at Murdoch Children's Research Institute (MCRI), said the drivers of parents' vaccine indecision were often complex.
"Under-vaccination is always painted as vaccine hesitancy or refusal. What we're now finding is that its access issues," she said.
Ms Danchin said under-vaccination was often underpinned by challenges around time, proximity to a vaccine provider, and affordability, despite the many government-funded provisions already available.
"Most relate to parents working full-time, or they can't afford the gap payment, public transport and petrol costs, or paying the GP out of pocket."
Measles prevention requires an MMR- MMRV combination vaccination to be taken in two doses. These can be taken for free by children aged 12 and 18 months under the NIP.
Some eligible people over this age threshold can also receive a free "catch-up" vaccine, but it is usually a paid service with a vaccination provider.
Low immunisation coverage is difficult to categorise by any one type of region, with pockets of low coverage in both rural and inner-city areas across the country.
Community clusters in areas of south-west WA, central NT, north and south-east Queensland, and northern NSW have all had below average child vaccination rates for measles according to the NCIRS's 2020 dataset.
The Byron Bay and Richmond Valley councils had some of the lowest at about 82 per cent.
Need for social, behavioural responses
Along with access impediments, under-vaccination is also influenced by cultural and religious beliefs, mistrust and scepticism of the efficacy of vaccines, and antipathy towards the medical system.
Ms Danchin says the solutions revolve around addressing parents' specific inhibitions.
"Trust is the major issue in many cultural groups," she said.
"We need social and behavioural responses. A broad-brush campaign of spending millions on TV advertising doesn't cut through."
She stressed the importance of a grassroots approach, which uses community "champions" like educators, faith leaders, and social workers to engage with parents and bridge the gap between them and their doctors.
"GPs need to have really good communication skills to avoid belittling parents when talking to them," she said.
"We need to work on building interpersonal communication, resources they can refer to online, and face-to-face workshops where people get to practice how to respectfully create engagement."
To improve ease of access, she said quick healthcare provisions were the key.
"One idea is vaccine trucks, or we can have more pop-up clinics on weekends, expand pharmacy vaccination for younger children, or raise the age for free vaccines," she said.
"We need to get creative about how we approach this issue."
Measles: What to know and do
Measles is an airborne illness transmitted through breathing in cough or sneeze droplets of an infected person, or person-to-person contact.
Symptoms typically included a prominent red rash, fever, and sore eyes. These usually appear five to 10 days after exposure, and last for about a week, with most people recovering without medical intervention.
Severe complications, including pneumonia, and inflammation of the brain or ear, can arise in some cases, leading to hospitalisation and even death.
There is currently no treatment and while the mortality rate has declined, those infected are advised to consult with a doctor straight away for tailored relief measures.
Antibiotics are ineffective given that the disease is caused by a virus and not bacteria.
From the day of exposure to measles particles, an infected person stays contagious until about four days after the rash appears, so it is advised to try and stay home.
The infection typically eases with ample rest, hydration, and painkillers to subside fever.
Although prevalent among children, measles can impact people of any age who are unvaccinated, have a weakened immune system or pre-existing medical conditions.
"If we have really high vaccination rates, we really do protect the whole community enormously from the diseases in the international community that can spread here," Chris Maher said.
"A real positive debate about getting kids vaccinated is much needed."