The impetus for this proposed shift in policy stems from a stark disparity between current global health guidelines and the biological reality of infant immunity in the modern era. Currently, the World Health Organization (WHO) recommends a two-dose measles vaccine schedule for all children, with the first dose typically administered between 9 and 12 months of age. This timing was historically based on the assumption that maternal antibodies—immunity passed from mother to child during pregnancy—would provide a sufficient shield for the infant during the first several months of life. However, the systematic review led by MCRI indicates that this protective window is closing much earlier than previously thought, particularly in low- and middle-income countries.
Published in the prestigious Journal of Infectious Diseases, the review represents a massive undertaking in pediatric immunology, synthesizing data from 34 separate journal articles. The researchers analyzed health data from 8,000 babies under nine months of age across various low- and middle-income nations. The findings were concerning: while 81 per cent of infants possessed maternal measles antibodies at the time of birth, those levels plummeted with alarming speed. By the time infants reached four months of age, only 30 per cent retained enough maternal antibodies to be considered protected. By seven months, that figure dropped further to a mere 18 per cent.
This data reveals a "protection gap" of several months where the vast majority of infants have lost their innate maternal immunity but have not yet reached the age required for their first scheduled vaccination. With 70 per cent of babies essentially defenseless by four months old, the current WHO recommendation of waiting until 9 to 12 months for the first dose leaves a significant portion of the global infant population at high risk during a period when the measles virus can be most devastating.
Dr. Lien Anh Ha Do, a lead researcher at MCRI, emphasized that the study’s findings provide a compelling case for earlier intervention. According to Dr. Do, when a first dose of the vaccine was administered to infants between four and seven months of age, it produced a positive immune response and proved to be highly effective in preventing the disease. She noted that an early first dose could provide sustained protection throughout infancy by closing the current gaps in immunity. This could be achieved either by moving the initial dose to an earlier age or by introducing a supplemental early dose into the existing two-dose routine. The goal is to ensure that infants do not spend nearly half of their first year of life without any form of protection against one of the world’s most transmissible diseases.
However, the proposal to lower the vaccination age is not without its complexities and potential drawbacks. Professor Kim Mulholland, a senior researcher at MCRI, pointed out that several significant barriers must be addressed before such a policy could be implemented globally. One of the primary concerns is the potential for an earlier first dose to reduce the vaccine’s overall efficacy as the child grows older. In immunology, there is a phenomenon where the presence of even low levels of maternal antibodies can interfere with the body’s long-term immune response to a vaccine, a trade-off that health officials must weigh carefully.
Furthermore, the logistical and financial strain on healthcare systems cannot be ignored. Many low- and middle-income countries are already struggling to maintain the current two-dose schedule. Professor Mulholland noted that adding a third dose to the program would be an immense challenge for nations that are currently failing to reach adequate coverage with the second dose. There are also the perennial issues of vaccine hesitancy and the cost-effectiveness of expanding the program, which require a nuanced approach to public health policy.
The role of transmission also complicates the strategy. While infants are the most vulnerable to severe outcomes, they are not the primary drivers of the virus’s spread. Professor Mulholland explained that school-aged children remain the key transmitters of measles. Therefore, while protecting infants is a moral and clinical priority, the broader goal of measles elimination still relies heavily on preventing infections among older children to limit the overall circulation of the virus in the community.
The urgency of this debate is underscored by the current state of the global measles outbreak. The virus is a highly contagious airborne pathogen that requires a very high level of population immunity to be kept at bay. Darren Ong, a researcher at MCRI, explained that to attain herd immunity and effectively stop the transmission of measles, at least 95 per cent of a population must receive both the first and second doses of the vaccine. Achieving and maintaining this level of coverage has proven to be an uphill battle in recent years.
The COVID-19 pandemic significantly exacerbated the situation, dealing a heavy blow to global immunization efforts. Routine vaccination programs were interrupted, catch-up campaigns were delayed, and the rise of vaccine hesitancy—fueled by misinformation during the pandemic—has created a "perfect storm" for measles to return. Mr. Ong noted that poor vaccination coverage has sparked large-scale outbreaks in several countries since the beginning of 2024. The statistics are sobering: nearly 400,000 measles cases were reported globally in 2024. The trend appears to be accelerating, with more than 16,000 cases recorded in just the first two months of 2025.
For young babies who rely on herd immunity because they are too young for the vaccine under current guidelines, these outbreaks are particularly perilous. Measles can lead to severe complications in infants, including pneumonia, brain swelling, and permanent disability or death. The failure to maintain the 95 per cent immunity threshold means the virus can find these unprotected pockets of the population with ease.
Associate Professor Claire von Mollendorf of MCRI argues that the lack of progress in measles control over the last two decades suggests that the current strategies are no longer sufficient. She warned that without new and innovative approaches to managing the crisis, the global health situation is likely to deteriorate further. Among the solutions she proposes is the implementation of rapid diagnostic testing, which would allow for better surveillance and earlier detection of outbreaks. This would enable public health officials to respond more quickly and precisely to local surges.
Additionally, Associate Professor von Mollendorf called for new randomized control trials to specifically evaluate the effectiveness of an earlier dosing schedule. Such trials would provide the hard evidence needed to determine if the benefits of early protection outweigh the risks of potentially reduced long-term efficacy. These studies are essential for protecting the millions of babies who are currently left in the "immunity gap," inadequately protected by their mothers’ antibodies and ineligible for the vaccine.
While the global debate continues, some regions are already taking proactive steps based on the emerging data. New Zealand, for instance, has recently updated its recommendations to allow for an additional measles dose to be given to children as young as four months of age if they are traveling to countries where the disease is endemic. This policy shift reflects a growing recognition that the risk of exposure in high-outbreak areas outweighs the traditional concerns regarding the timing of the first dose.
The MCRI review serves as a wake-up call for the international health community. It highlights a critical flaw in the current defense against measles: a biological mismatch between when an infant’s natural protection ends and when their medical protection begins. As the global case count continues to climb in 2025, the pressure to reform vaccination schedules is mounting. The challenge for the WHO and national health departments will be to balance the immediate need to protect vulnerable infants with the long-term logistical and immunological goals of measles elimination. In a world where a highly contagious virus can cross borders with ease, the window for closing the immunity gap is narrowing, and the cost of inaction continues to rise.
