A recent systematic review led by the Murdoch Children’s Research Institute (MCRI) has sounded an alarm over the widening immunity gap in infants during the current global measles outbreak. Published on May 29, 2025, in The Journal of Infectious Diseases, the study underscores that maternal antibodies, which confer passive protection to newborns, wane far earlier than previously assumed—leaving a substantial proportion of babies vulnerable long before they become eligible for routine vaccination at nine months of age.
Waning Maternal Antibodies: A Critical Vulnerability
Decline in Passive Protection
The MCRI review analysed 34 peer-reviewed studies encompassing data from over 8,000 infants under nine months across low- and middle-income countries. It found that while approximately 81 percent of newborns possess protective measles antibodies at birth, this rate plummets to just 30 percent by four months and dwindles further to 18 percent by seven months. Such rapid depletion starkly contrasts with the World Health Organization’s recommendation to administer the first measles vaccine dose between nine and twelve months of age.
“With 70 percent of babies having no measles antibodies present by four months old, they are being left unprotected before reaching vaccine-eligible age,”
— Dr Lien Anh Ha Do, MCRI
Implications for Outbreak Control
Measles is among the most contagious human pathogens, demanding herd immunity thresholds of at least 95 percent coverage with two vaccine doses to interrupt transmission. However, routine immunisation programs in many resource-constrained settings struggle to achieve even 80 percent coverage for the first dose, let alone the second. The COVID-19 pandemic exacerbated these challenges by disrupting vaccination campaigns and fueling vaccine hesitancy, contributing to the nearly 400,000 measles cases reported globally in 2024 and over 16,000 cases in the first two months of 2025.
Evaluating Earlier or Additional Doses
Immune Response in Early Infancy
The review highlights evidence that administering an early measles vaccine dose between four and seven months elicits a robust immune response. Infants vaccinated in this window produced protective antibody titres comparable to those vaccinated later, suggesting that an “extra” early dose could close the immunity gap without compromising subsequent routine doses.
“An early first measles dose could provide sustained protection throughout infancy by closing gaps in immunity,”
— Dr Lien Anh Ha Do, MCRI
Potential Schedules Under Consideration
Two principal strategies emerge from the data:
- Shift the First Dose Earlier
- Move the current nine-month dose to as early as four or six months during high-risk periods or in outbreak settings.
- Pros: Ensures infants attain active immunity before exposure risk peaks; aligns with emergency vaccination precedents where a six-month dose supplements the routine schedule.
- Cons: Maternal antibodies may still interfere in some babies if administered too early, potentially reducing vaccine efficacy.
- Add an Extra Early Dose
- Retain the routine two-dose schedule (nine and 15–18 months) while introducing an additional dose at four to six months.
- Pros: Provides layered protection; mitigates immunity gaps without altering existing schedules.
- Cons: Increases programmatic complexity and costs; risks lower uptake given resource constraints.
Barriers to Implementation
Cost-Effectiveness and Logistics
Implementing an additional or earlier dose entails increased vaccine procurement, cold-chain demands, and healthcare workforce capacity. Many low- and middle-income countries already struggle to deliver the current two-dose regimen reliably. Professor Kim Mulholland of MCRI warns, “Adding a third dose will be challenging given that low- and middle-income countries are already struggling to administer a second dose within the current measles vaccination program.”
Vaccine Hesitancy and Uptake
Public confidence in vaccines remains uneven, with misinformation campaigns and logistical hurdles hindering timely uptake. Introducing a new dosing schedule may exacerbate hesitancy. Educational campaigns and community engagement will be critical to overcome skepticism and ensure parents understand the urgency and safety of early vaccination.
Potential Trade-Offs in Efficacy
Earlier vaccination could accelerate the decline of vaccine-induced antibodies. Some immunologists caution that while an early dose triggers a primary immune response, the accelerated waning of antibodies could leave older infants less protected. Balancing the benefits of early protection against the risk of shortened immunity duration requires careful modelling and prospective trials.
Expert Calls for Further Research
Need for Randomised Controlled Trials
While observational studies provide compelling evidence, MCRI researchers advocate for new randomised controlled trials (RCTs) to evaluate the immunogenicity, safety, and duration of protection conferred by early or additional measles doses. Such trials would help define optimal timing and dosing intervals tailored to different epidemiological contexts.
“New randomised control trials to evaluate the effectiveness of an earlier dosing schedule would help protect babies inadequately shielded by maternal antibodies,”
— Associate Professor Claire von Mollendorf, MCRI
Enhancing Surveillance and Diagnostics
Rapid diagnostic tools and strengthened surveillance systems are equally essential. Early detection of measles outbreaks enables swift deployment of targeted vaccination campaigns. MCRI researchers urge investment in point-of-care tests and real-time reporting platforms to guide timely public health responses.
Global and Local Policy Responses
WHO Recommendations and Country Innovations
Currently, the WHO endorses a two-dose measles vaccination schedule—first at nine months and second at 15–18 months—with a six-month dose in outbreak settings. Some countries have already moved to adapt these guidelines. New Zealand, for example, now recommends an extra dose at four months for infants traveling to measles-endemic regions.
Policy Debates Underway
National immunisation technical advisory groups (NITAGs) in several countries are convening urgent debates on adjusting infant schedules. Policymakers must weigh global recommendations against local epidemiology, resource availability, and population acceptance. The MCRI review has catalysed discussions in the Asia-Pacific region, where recent outbreaks have stressed health systems and underscored the costs of delayed vaccination.
The Human Toll and Broader Public Health Imperatives
Impact on Vulnerable Populations
Infants under nine months suffer the highest measles morbidity and mortality when exposed. Complications such as pneumonia, encephalitis, and malnutrition can have lifelong consequences for survivors. Closing immunity gaps early is thus not only a matter of individual protection but also of safeguarding community health.
Herd Immunity and Outbreak Prevention
Achieving and maintaining 95 percent coverage with two doses is the global benchmark for measles elimination. Until that target is met, infants remain dependent on both maternal antibodies and high community immunity. Early vaccination strategies can bolster infant protection without undermining herd immunity goals, provided coverage remains uniformly high.
Interlinkages with Other Health Interventions
Integrating early measles vaccination with existing maternal and child health services—such as routine postnatal visits, nutritional supplementation programs, and other infant immunisations—could improve efficiency and uptake. Health system strengthening, including workforce training and supply-chain optimization, will amplify the impact of any schedule changes.
Conclusion: A Critical Juncture in Measles Control
The resurgence of measles poses a severe threat to global child health, exposing the fragility of existing immunisation frameworks. The MCRI’s findings demand an urgent reassessment of infant vaccination schedules to bridge the immunity gap left by waning maternal antibodies. While logistical, financial, and behavioural challenges loom large, the potential benefits—averting thousands of infant cases and restoring progress toward measles elimination—are immense. As policymakers, researchers, and international agencies convene in the coming months, robust evidence from new trials, enhanced surveillance, and community engagement will be pivotal to crafting effective, equitable, and sustainable immunisation strategies for the world’s youngest and most vulnerable
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