What's happening that has led to 40,000 infections in popular tourist destination Vietnam?

Amid a global measles epidemic, the number of measles cases has surged in Vietnam, a popular tourist destination, this year, prompting the government to launch an emergency response.
According to local Vietnamese media on the 18th, there are approximately 40,000 suspected measles cases in Vietnam this year.
Vietnam's Ministry of Health said the number of deaths in the past three months was the same as the number of deaths in the whole of last year, and issued a measles alert.
Of the infected patients, 72.7% were between 9 months and 15 years old, with 15.3% being under 9 months old.
The southern region, including Ho Chi Minh City, had the highest share at 57.0%, followed by the central region (19.2%), the north (15.1%), and the Central Highlands (8.7%).
According to the World Health Organization (WHO), measles will rapidly increase in many countries from 2024 onwards due to vaccination rates below 80%.
Last year, there were an estimated 310,000 cases of measles worldwide, including 100,000 in Europe, 90,000 in the Middle East, and more than 30,000 in Southeast Asia.
Vietnam's Prime Minister Pham Minh Chinh has issued an urgent directive to expand measles vaccinations and complete them by the end of this month. The Ministry of Health said measles cases are on the rise across the country.
"We expect the number of cases to continue to rise, and we have instructed each region to closely monitor the situation and take thorough measures," he said. In particular, there are areas with poor access to medical services, such as mountainous areas where ethnic minorities live, and where vaccination rates are low.
Officials are concerned that it is vulnerable.