News from the lab
Cross-postsMaternal and child health
Breaking the taboo on including pregnant women in vaccine clinical trials
- 29 July 2026
- 8
min read - byPATH
A health care worker prepares a meningitis vaccine. Photo: PATH/Gabe Bienczycki.
The meningococcal meningitis landscape has changed dramatically over the last 15-plus years with the introduction of affordable, effective vaccines to the African meningitis belt. First came MenAfriVac®, the serogroup A conjugate vaccine that eliminated meningitis A—a groundbreaking achievement that proved meningitis control was possible. Then came MenFive®, a multivalent conjugate vaccine that has the potential to eliminate all epidemic-causing serogroups from the meningitis belt and make meningococcal meningitis a thing of the past.
There is more work to be done—including introducing MenFive (and future multivalent meningococcal conjugate vaccines) into routine immunization programs and conducting one-time multi-age vaccination campaigns across the meningitis belt—but already, the cloud of fear caused by the disease is lifting
Now we’re studying the safety and immunogenicity of MenFive in pregnant and breastfeeding women
It might not sound like a particularly remarkable undertaking, especially given the already-robust evidence base for MenFive, but it is a hugely significant milestone
Why? Because when vaccines are being developed for the general population, pregnant and breastfeeding women are regularly excluded from clinical trials
PATH has long championed vaccine research and access for pregnant women. Along with our partners, we’ve advanced knowledge and development of maternal vaccines that target respiratory syncytial virus, Group B Streptococcus, pertussis, and influenza
This study broadens our commitment to maternal health by prioritizing action toward a longstanding knowledge gap. Pregnant women are no less susceptible to disease than non-pregnant people; they should have no less access to lifesaving vaccines
We’re eager to advance the evidence base for meningococcal vaccines and help ensure MenFive clinical data are available for everyone, throughout all of life’s experiences
A history of omission
Pregnant and breastfeeding women are not typically excluded from vaccine clinical trials due to evidence of a heightened—or even theoretical—safety risk. In fact, safe and effective vaccination during pregnancy is well-established, with a wide range of vaccines regularly recommended and administered
Rather, the reasons are rooted in hard-to-forget history lessons. After use of the drug thalidomide in pregnant women in the 1950s and 1960s caused devastating birth defects, global regulatory bodies issued policies banning women of childbearing age from participating in clinical research
In practice, this led to all women being excluded, which has had profound impacts that continue to this day—including a lack of clarity around how disease presents, and drugs and therapies operate, in male versus female bodies; a hesitancy to prescribe medications as readily to women as to men; and an erosion of trust between health care workers and patients
US policy was changed in 1989, but it wasn’t until 1993 that a law mandating the inclusion of women and minorities in US government-funded research was passed, and 1998 that global regulatory authorities adopted guidelines specifying clinical trial participants should reflect the target patient population
The representation of women has grown as a result, but the same can’t be said for pregnant and breastfeeding women
Modern reasons for exclusion are complex and include a lack of distinction between pharmaceutical versus vaccine risks; physiological variables during pregnancy; extreme caution regarding risks to the fetus; the need for more specific clinical monitoring and more expensive liability insurance; fear of how any adverse events might be perceived; and a lack of regulatory mandates to include pregnant and breastfeeding women.
Importantly, not all clinical trials are appropriate for pregnancy. For example, Phase 1 studies demonstrate basic vaccine safety, and these are usually performed in young, healthy, non-pregnant adults to minimize risk as much as possible
The disservice comes in that pregnant and breastfeeding women are also excluded from the later stage clinical trials necessary to license a vaccine. This means that unless a vaccine was designed specifically to protect a baby via maternal immunization—and, therefore, pregnant women were the focus of the trial—regulators and public health officials have limited real-world performance data with which to assess the risk-benefit balance for pregnant and breastfeeding women.
As a result, World Health Organization (WHO) recommendations for vaccine use in pregnant or breastfeeding women are typically based on data from post-licensure observational studies rather than dedicated clinical trials—and they can lag years behind initial mass vaccination campaigns, leading to significant missed opportunities
This dearth of formal information is evident in the often-equivocal language in product labels. The influenza vaccine package insert, for example, historically stated that because there were no adequate and well-controlled studies in pregnant women, the vaccine should be used only if clearly needed. Yet, health care providers fully recommended it for pregnant women given their heightened vulnerability to the virus and the vaccine’s real-world performance.
These caveats and contradictions paint a picture of uncertainty that can cause many pregnant and breastfeeding women to hesitate—and even decline essential preventative care
To increase information equity, improve vaccine access, and strengthen decision-making, pregnant and breastfeeding women should be presumptively included in clinical trials—and only excluded (for) overriding scientific evidence
Remaking the status quo
To increase information equity, improve vaccine access, and strengthen decision-making, pregnant and breastfeeding women should be presumptively included in clinical trials—and only excluded if there is overriding scientific evidence to do so
The COVID-19 pandemic gave this argument a global stage
When the first vaccines became available, experts saw no biological reason they would pose any particular risk to pregnant women or their fetuses. But the initial clinical studies explicitly excluded pregnant women, so there was limited data to back that assumption up
Some national immunization advisory groups at first declined to issue advice to pregnant women other than to consult their health care providers. Without data, though, providers didn’t know how to advise their patients. Pregnant women were largely left to make decisions on their own
This lack of inclusion in clinical research has been a recognized problem for decades, but such a visible example prompted forceful calls for change. Parents, scientists, health care providers, and public health experts are all speaking out about the need for better information for pregnant women as soon as possible. Global regulators are designing guidelines for including pregnant and breastfeeding women in clinical trials. And, importantly, vaccine manufacturers are heeding this call and gradually beginning to add pregnancy trials to their development strategies at earlier stages.
Expanding meningitis vaccine options
Meningococcal meningitis is a deadly bacterial infection and one of the most significant public health threats in sub-Saharan Africa. It can occur anywhere in the world but is most prominent in the meningitis belt, a 26-country region stretching from Senegal to Ethiopia. Meningococcal epidemics are a terrifying annual threat here, where, at their largest, they have claimed tens of thousands of lives in a single season.
The disease sets in rapidly and can kill within hours. Even with prompt antibiotics, it kills ten percent of infected people within two days of symptom onset. Survivors are often left with severe, lifelong complications like brain damage, hearing loss, or limb amputations
And infection in the context of pregnancy or breastfeeding means both mother and child are at risk
WHO recommends that meningococcal conjugate vaccines be given during pregnancy and breastfeeding. Yet, because there were no formal clinical studies of MenFive in pregnant or breastfeeding women, the vaccine’s label—which comes from the national licensing authority, not WHO—states that administration should only be considered when the potential benefits outweigh any potential risks for the mother and fetus.
Researchers can be reasonably certain of MenFive’s suitability for pregnancy based on its existing clinical data base in several thousand individuals; the fact that other meningococcal conjugate vaccines have been studied and used safely in pregnancy for years; and that incidental pregnancies during the original MenFive clinical trials raised no safety issues
But PATH’s study can confirm those assumptions. In line with an accompanying WHO call for more clinical data, we’re sponsoring a Phase 3 clinical trial to evaluate the safety and immunogenicity of a single dose of the vaccine in 200 pregnant and breastfeeding women and their infants in Mali. The trial began in May 2026 with results expected in 2028
MenFive—developed by PATH and the Serum Institute of India Pvt. Ltd., with funding from the UK government’s Foreign, Commonwealth & Development Office—received WHO prequalification for use in people between 9 months and 85 years of age in 2024. It has since been used for outbreak response in several African countries and introduced in the routine childhood immunization schedule in Niger
With more countries expected to follow suit in the coming years, our study will provide timely evidence for removing pregnancy and breastfeeding cautions from MenFive’s product label—expanding its use in future campaigns, enabling policy and decision-makers to more thoroughly protect their populations, and helping pregnant and breastfeeding women feel confident saying ‘yes’ to MenFive
Importantly, strengthening the MenFive evidence base and improving access for broader populations aligns with WHO’s global effort to defeat meningitis by 2030—a primary goal of which is to significantly reduce deaths due to vaccine-preventable bacterial meningitis
This study can help us get there. And, with the study design serving as an affordable, efficient model for meaningful clinical evaluations of other vaccines in pregnant women, it can help move vaccine research toward inclusivity
Including pregnant and breastfeeding women in clinical studies undoubtedly adds a level of complexity to vaccine research, but it shouldn’t be avoided due to difficulty. Pregnant women are a medically complex population about whom more data are needed, not less—and no one should ever have to choose between forgoing a lifesaving vaccine or receiving one without fully understanding the benefits and risks.
Studies like this one are crucial for shifting that paradigm. PATH is proud to be a part of it
