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SINGAPORE: The most contagious disease known to humans is making a comeback.

The United States reported 1,001 confirmed measles cases and three deaths as of Friday (May 9), a dramatic increase from 285 cases and no deaths for the whole of 2024. Declared to have eliminated measles by the World Health Organization (WHO) in 2000, the US risks losing that status by 2026, if this trend continues unchecked.

Measles cases have also been on the rise across Europe, with nearly 6,000 reported to the European Centre for Disease Prevention and Control this year.

Closer to home, 2,584 confirmed measles cases were reported in the WHO Western Pacific Region in the first three months of 2025, 50 per cent more compared to the same period in 2024. Of the seven Southeast Asian countries covered in this grouping, ongoing spread has been reported in Cambodia, Laos, Malaysia, the Philippines and Vietnam. Brunei and Singapore have eliminated measles in 2015 and 2018 respectively.

Measles is seen as the “canary in the coal mine” by public health professionals due to its extreme contagiousness. A single infected person can spread the virus to between 12 and 18 susceptible individuals – about twice as contagious as chickenpox and several times more than COVID-19 or influenza.

In the ongoing US outbreak, 30 per cent of cases are under 5 years of age, with one in four of this group requiring hospitalisation. Two children, aged six and eight, were among the confirmed deaths.

The WHO estimated that over 100,000 persons – mostly children under 5 – died worldwide from measles in 2023. In high-income countries such as the US and Singapore, the death rate from measles is about one in 1,000 cases.

A PREVENTABLE TRAGEDY

Many of these deaths are preventable. A highly effective vaccine against measles has been commercially available since 1963 and the widespread use of different vaccine formulations has saved an estimated 94 million lives over the past half-century – more than all other vaccine-preventable diseases combined except smallpox.

A dangerous convergence of factors - largely unfortunate legacies of the COVID-19 pandemic – is fuelling the spread of the measles virus.

Most importantly, vaccination rates declined across many countries as children missed routine immunisations due to pandemic disruptions. Immunisation services were also slow to recover post-pandemic.

Simultaneously, vaccine hesitancy has also risen significantly. It has been systematically amplified by the proliferation of dis- and misinformation – particularly across social media – deepening distrust in public health institutions. Top US public health official Robert Kennedy Jr's tepid endorsement of measles vaccination coupled with occasional promotion of evidence-free treatment options such as cod liver oil have not helped, at least in the US.

Because the measles virus is so contagious, herd immunity generally requires population vaccination rates of at least 95 per cent. This makes it hard for the virus to spread, protecting those who cannot be vaccinated such as those with specific allergies and the severely immunocompromised (who cannot receive live vaccines).

Even a slight fall in vaccination coverage can create pockets of vulnerability. In the ongoing US outbreak, almost all of the cases were unvaccinated.

The presence of community cases of measles often signals faltering immunisation programmes, with other vaccine-preventable diseases to follow if nothing is done.

More frequent measles outbreaks often signal deeper issues in a country’s public health system and may be precursors to further public health emergencies. Conversely, the sustained elimination of measles generally indicates a well-functioning public health system.

MEASLES CRISIS LIKELY TO WORSEN

This crisis is likely to worsen in the near future.

The US has long been a cornerstone of global immunisation efforts through bilateral and multilateral aid. The most significant of the latter is Gavi, the Vaccine Alliance which saw its billion-dollar grant cancelled by the Trump administration in March. This public-private partnership was established specifically to increase vaccine access in low- and middle-income countries and has helped vaccinate over 1 billion children worldwide.

Just as concerning is the uncertain future of the Global Measles and Rubella Laboratory Network coordinated by the WHO, which spans over 760 laboratories in more than 150 countries and is critical for global measles surveillance. With the US as its sole funder, the impending US withdrawal from the WHO will significantly cripple the network and surveillance efforts.

WHY IT MATTERS TO SINGAPORE

Can Singapore ignore this global surge? After all, close to 97 per cent of children here have received at least one dose of the MMR (mumps, measles and rubella) vaccine, theoretically preventing sustained spread of the virus. The Communicable Disease Agency has reported only eight cases of measles in Singapore since the start of 2025.

But we are not immune to the global measles situation.

Infants under one year of age are particularly vulnerable – they are too young to receive their first MMR dose under the current National Childhood Immunisation Schedule. Those who have received only a single dose of the vaccine and adults vaccinated decades ago may no longer enjoy full immunity.

The rise in global measles cases will mean more frequent importation of the virus into Singapore and higher risk of exposure for residents who travel overseas. Both scenarios may potentially lead to localised outbreaks, especially in settings such as infant care centres.

REVERSING A DANGEROUS TREND

The pending void created by recent cuts in international aid cannot be easily filled, if at all.

However, countries with established expertise and capacity – including Singapore – could consider increasing contributions to regional vaccination efforts and outbreak response capabilities through bilateral partnerships or regional mechanisms such as ASEAN and the WHO Regional Office.

Such investments should neither be viewed as purely diplomatic gestures nor drains on national resources. They represent strategic and effective public health protection for the contributing countries themselves, reducing the risk of measles or other communicable diseases crossing borders.

It is important to recognise that measles vaccination is one of the “best buys” in public health intervention. For every dollar spent on measles vaccination, countries are estimated to receive up to US$58 in economic and social returns from reduced healthcare costs to increased productivity of those who would otherwise have been felled by the virus. Few public health interventions deliver such extraordinary returns.

Singapore must continue to ensure high vaccination rates and vigilance for more imported cases. This requires us to counter vaccine misinformation and address hesitancy.

We must robustly challenge misconceptions spread by anti-vaccine activism. Measles is not a mild childhood illness. The MMR vaccine is safe and is not associated with autism – the notorious study that made this claim has been debunked as fraudulent.

Measles is a test of a public health system’s strength. With the global surge in cases, the proverbial canary in the coal mine has sounded a clear warning against complacency, even for countries that have eliminated measles.

Professor Hsu Li Yang is Director, Asia Centre for Health Security at the Saw Swee Hock School of Public Health, National University of Singapore.