Measles cases went up 255 percent from 2022 to 2023 in the World Health Organisation (WHO) Western Pacific Region, an increase caused by gaps in vaccination coverage and disease surveillance and travel of people from countries experiencing outbreaks.

The Western Pacific Region had lower levels of measles infections in 2021 (1080 cases) and 2022 (1422 cases), but in 2023 cases jumped to 5044. Declines in vaccination coverage in several Western Pacific countries during the COVID-19 pandemic, ongoing measles outbreaks in the Philippines and persistent endemic measles transmission in Malaysia all pose a threat of measles resurgence in the Region in 2024−2025.

Although the Western Pacific did not experience large measles outbreaks on the scale seen in other regions of the world in 2023, 3.6 million children in this Region missed their routine immunisations during 2020−2022. The resurgence of measles worldwide increases the risk of importation to countries throughout the Western Pacific, including those where measles had previously been eliminated.

Measles is one of the most infectious diseases on earth, spreading easily when an infected person breathes, coughs or sneezes. A single person infected with measles can potentially infect 12 to 18 additional people, and the disease can lead to severe complications and death. However, it is almost entirely preventable through two doses of measles vaccine. From 2000 to 2022, measles vaccinations prevented 57 million measles deaths worldwide.

“Anytime there’s measles in a community, it is a threat. Even countries that have achieved elimination can’t relax. They have to maintain high coverage of measles vaccination and strong systems for picking up cases that get imported through international travel. Without this, measles transmission can become re-established,” says Dr Saia Ma’u Piukala, WHO Regional Director for the Western Pacific.

If measles is imported into communities where vaccination coverage is below 95%, the risk of outbreaks increases. Countries and areas in the Western Pacific are working hard to close immunity gaps.

Supporting countries to reduce immunisation gaps, increase surveillance

From 2022 to 2023, 11 countries in the Western Pacific − Fiji, Kiribati, Marshall Islands, the Federated States of Micronesia, Mongolia, Palau, Papua New Guinea, the Philippines, Samoa, Solomon Islands and Viet Nam − conducted nationwide measles and rubella vaccination campaigns or catch-up vaccination activities. Cambodia and the Lao People’s Democratic Republic are planning nationwide measles and rubella vaccination campaigns this year. However, more needs to be done to ensure countries in the Region maintain robust immunity through vaccination, especially among populations that are harder to reach and people who are travelling.

Strong early warning and disease surveillance systems with complete case investigations are also vital for health authorities to quickly find and confirm potential measles or rubella cases before they become a larger outbreak.

“The Western Pacific must not forget the bitter lessons we have learned from previous measles resurgences in the Region,” says Dr Saia Ma’u Piukala. “Countries must keep working to reach every child with lifesaving vaccines, strengthen surveillance systems, encourage health workers to stay vigilant and educate people about the importance of checking that their vaccinations are up-to-date so we can avoid a resurgence in the future.”

Countries working towards measles elimination

The Western Pacific Region continues to make progress towards eliminating measles, as part of the Regional Strategy and Plan of Action for Measles and Rubella Elimination endorsed by Member States in 2017. Elimination means there has been no prolonged local transmission of the virus in a country for at least three years, and progress is reviewed annually to verify that elimination has been maintained.

Currently, eight countries and areas in the Western Pacific Region are verified as having eliminated measles: Australia, Brunei Darussalam, Hong Kong SAR (China), Japan, Macao SAR (China), New Zealand, the Republic of Korea and Singapore.

Other countries and areas in the Region are also working hard to achieve measles elimination. Among these, the group of 21 Pacific island countries and areas1 (considered as one epidemiological block for disease elimination purposes) are currently on track to eliminate measles and rubella by 2025. After a measles outbreak in the Pacific in 2019, intensified efforts were taken to improve vaccination coverage and surveillance for the disease. Since early 2020, there appears to have been no ongoing transmission of measles or rubella in the Pacific island countries. But it is essential to remain vigilant.

Through regularly conducted vaccination campaigns and catch-up activities, great work has been done to close immunization gaps in the Pacific. In addition, WHO is working with Cook Islands, Kiribati, Samoa, Solomon Islands, Tonga and Vanuatu to expand serology and molecular testing for measles and rubella in laboratories in the Pacific. Additional equipment and training are due in the coming months.

Mongolia was verified for measles elimination in 2014, but unfortunately lost its status in 2016 following ongoing outbreaks. The country is now working hard to be re-verified for the elimination of measles. Mongolia conducted a preventive nationwide measles and rubella vaccination campaign in 2023 and is implementing a road map, developed in collaboration with WHO, towards measles and rubella elimination by 2025.

WHO is closely monitoring the epidemiological situation, surveillance performance and vaccination coverage for measles and rubella in the Region based on data reported from Member States, and publishes a monthly bulletin on the measles and rubella situation in the Region.

WHO continues to work with countries to achieve elimination by ensuring that their immunisation programmes can deliver two doses of the vaccine to every person who needs it. The Organization is also working with countries to strengthen laboratory testing capacity, referral and surveillance systems, and data management to detect possible cases, and avoid a large-scale resurgence of measles in the Region.

What the public and health workers can do

Members of the public should ensure that they are fully protected with two doses of measles-containing vaccine. This is especially important for travellers who, if unvaccinated, could expose young children and other vulnerable people in communities to which they are traveling to infection. It is also vital for health workers to ensure their patients are fully vaccinated and they can recognize and report possible cases of measles to prevent outbreaks.

World Immunisation Week, 24−30 April 2024, will celebrate the 50th anniversary of the Expanded Programme on Immunisation (EPI) – an initiative launched by WHO in 1974 to ensure equitable access to life-saving vaccines for every child, regardless of their geographic location or socioeconomic status. This milestone offers an opportunity to celebrate the programme’s success in preventing diseases and advancing health equity, and call attention to the need to further protect future generations from vaccine-preventable diseases, including measles.