Increasing Measles Cases across the Americas

Measles outbreaks have been reported in 10 countries in the Americas region in 2025.

According to PAHO (Pan American Health Organisation), 10, 139 cases of confirmed measles have been notified up to August 8, 2025. This represents a 34-fold increase compared to the previous year. It is a major concern for the region. There were 18 measles-related deaths.

The report highlights a low vaccination coverage rate as the main factor for the dramatic increase in cases. It also shows a major deterioration in vaccine coverage since the COVID -19 pandemic. Vaccination rates are well below the 95% level required to stop transmission.

Geographic spread and key outbreaks

Over 90% cases were reported in three countries (Canada, United States and Mexico). Canada and the United States had previously interrupted transmission of the disease.

It remains to be seen whether they will retain this status in the next 12 months.

On a positive note, there have been no new cases in Texas since late July - Texas was the epicentre for a major measles outbreak in the Mennonite community.

Measles situation in Australia

Eighty-seven cases of measles have been notified to Australia’s surveillance system up until July 20th this year (2025). There were 41 notifications to this time in 2024.

This is disappointing given the level of concern raised by the various State health authorities around Australia.

There were NO cases of measles reported for a similar period between January 1, 2021, and 18 July 2021 when our international borders were closed!

An important reminder for travellers

This recent report from PAHO and the previous European surveillance report in June are important reminders to travellers who might be visiting countries with suboptimal vaccination coverage.

While the risk of exposure might be low in Australia and many other countries, it cannot be taken for granted, even in the Americas and Europe (particularly eastern Europe).

Measles is a highly infectious disease, with over 90% of non-immune individuals exposed to the disease will become symptomatic.

The global risk of measles has increased over the last 2 years.

All travellers, particularly those born after 1966, should review their measles vaccination status before departure. Special attention must be given to infants travelling to high risk destinations.

Maternal immunity and infant protection

Early waning of maternal antibody is an important concern. Maternal measles antibodies play a very important role in protecting infants from an early bout of measles. This transfer may not be achieved in premature infants and early measles protection must be considered if the child is at risk.

The level of protection is also influenced by maternal immunity. This immunity may be different in mothers with natural immunity and those with vaccine immunity.

In a longitudinal study of 221 infants and their mothers in Belgium, only 29% of the infants born to a vaccinated group were considered protected at 3 months compared to 60% in the naturally immune group. By 6 months, only 1 out of 31 had protective levels versus 10 out of 41 for the naturally immune group.

Neither group showed immunity at 9 months. This study can be sourced here.

It should be noted that mothers with vaccine immunity might receive natural boosting in countries where measles transmission persists. In those countries where transmission has been interrupted (Australia) natural boosting doesn’t occur.

Vaccination of infants over 6 months must be a consideration when travelling overseas.

Measles vaccination recommendation

• Infants 6–11 months of age should be considered for at least one dose of measles containing vaccine. Most mothers of today have vaccine immunity rather than natural immunity. This provides protection for a shorter period.
• Preschool children ≥12 months of age should have two doses of MMR vaccine separated by at least 28 days.
• School-age children should have two doses of MMR.
• Adults born in or after 1966 should have two doses of measles-containing vaccine.
• If administered at ≥ 12 months of age, one dose of measles-containing vaccine or MMR is 95% effective in preventing measles disease and two doses are 99% effective. One dose of measles-containing vaccine or MMR is approximately 85% effective if administered at 9 months of age.