20 Years of Rotavirus Vaccines: Q&A with Dr. Michelle Groome

Despite the introduction of oral rotavirus vaccines in over 100 countries, rotaviruses are still the leading cause of severe, dehydrating diarrhea in children aged less than 5 years in low- and middle-income countries. The disease caused an estimated 108,000 deaths worldwide in 2021.

Dr. Michelle Groome is a medical doctor and principal researcher in epidemiology at the Vaccine and Infectious Diseases Analytics Research Unit at the University of the Witwatersrand in Johannesburg, South Africa and a well-known expert in rotavirus disease. In anticipation of the upcoming 15th International Rotavirus Symposium taking place in Cape Town, South Africa September 30-October 3, 2025 — for which Groome is helping to plan as a member of the organizing committee — we asked her to share her thoughts on:

• Why the four rotavirus vaccines currently in use, which have significantly reduced child hospitalizations and deaths from the disease, appear to be less effective in low- and middle-income countries
• What research is being done to determine why
• Ongoing development of new, more effective vaccines and dosing schedules

Why is rotavirus so dangerous, particularly for children?

Rotavirus is still the most significant cause of diarrhea in childhood, especially in children under 2 years of age. Prior to introduction of the rotavirus vaccine, 40 to 50% of children who were hospitalized for diarrhea would have rotavirus isolated in their stool. Rotavirus can cause severe diarrhea, which can lead to dehydration. Children, especially young children, are very susceptible to dehydration and if they aren’t adequately rehydrated quickly enough, this can ultimately lead to death. So, rotavirus is also a leading cause of childhood death, especially in low- and middle-income countries.

This fight is personal for you, isn’t it?

I’ve been in research for the last 20 years and focusing on rotavirus for about 15 years of that. Prior to that, I was in clinical practice, and it was during this time that my eldest daughter contracted rotavirus when she was nine months of age. She had severe vomiting and diarrhea. As a clinician, I had treated many dehydrated babies, but it was really scary to see the deterioration in my daughter’s condition in a matter of hours. Fortunately, I was able to take her to a nearby hospital that evening and she could get an IV line and rehydration fluid. It really always just drives home the fact that for some parents there may not be a hospital close by, or they aren’t able to easily get transport to go to the hospital. Clinics may be closed because it’s nighttime, and in those situations a baby can really deteriorate over a couple of hours and actually end up dying before getting treatment. As a mom, it scared me. But I think it really did shape my interest in rotavirus and making a difference through preventing these situations.

So you’ve seen the benefits of vaccination against rotavirus firsthand…

At the Chris Hani Baragwanath Hospital, when I was still doing my internship and working in the hospital, there was a specific ward for treating the gastroenteritis babies. Rotavirus is seasonal, so usually it’s in the autumn-winter season. During that season, that ward used to be full of babies coming in with diarrhea, needing to get intravenous fluids. After we introduced the rotavirus vaccine, that ward was actually repurposed and no longer used as a gastro ward. There just weren’t enough babies to have this whole ward open for babies with diarrhea.

When we talk about the impact to policymakers, if they don’t understand all the stats or what it really means when we’re talking about percent reductions, this kind of a real-life example is a really impactful way to explain how the rotavirus vaccine can make a huge difference.

What impact have rotavirus vaccines had worldwide?

We now have four oral rotavirus vaccines that are WHO pre-qualified. At the moment, more than 100 countries have introduced rotavirus vaccines. This includes many low- and middle-income countries. That’s where the highest burden of severe disease — and especially mortality— from rotavirus occurs. Two of the vaccines were licensed several years ago and have been in use for a number of years. We’ve seen tremendous impact of these vaccines in terms of reducing the number of rotavirus hospitalizations and deaths globally.

Two vaccines from Indian manufacturers have come onto the scene more recently, which has really improved the global rotavirus vaccine supply. That means more children are able to access these vaccines. With four globally licensed vaccines, I think we have a good supply of oral rotavirus vaccines.

So why are there still so many rotavirus deaths?

There’s still a residual burden of severe rotavirus disease in many low- and middle-income countries which have introduced the vaccine. Studies have shown that the oral vaccines are not as effective in low- and middle-income countries compared to high-income countries. And I’ve done some work on that. We’re seeing about 40% to 60% effectiveness in low- and middle-income countries, as opposed to the greater than 80% effectiveness that we’re seeing in the high-income countries. But even this 40% to 60% protection is having a tremendous impact on rotavirus disease.

Do we understand why the rotavirus vaccines might not be as effective in low- and middle-income countries?

The lower protection afforded by the vaccines in lower-income countries is not something that’s unique to rotavirus vaccines. We’ve seen this with other oral vaccines too. There are several potential reasons for this and it’s likely to be a combination of factors. For one thing, there’s just a lot more circulation of the virus and more disease, and as a result, even adults are exposed to rotavirus. So pregnant mums in lower-income countries have higher levels of rotavirus antibodies which the mum passes to her baby through the placenta and also through breastfeeding. The breast milk is ingested by the baby and because this is an oral vaccine, there may be some interference between the maternal antibodies and the vaccine.

In low- and middle-income countries there are also a lot of other pathogens circulating, and we know these babies are exposed to a lot more infectious agents compared to those in high-income countries. We see differences in the gut microbiome, which are those “good” bacteria and organisms that are present in the gut. We also see a lot more malnutrition. All of these things can affect the way that the body responds to the vaccine.

Are parents hesitant to have their children take the rotavirus vaccine?

There are factors to consider in addition to vaccine hesitancy. One thing is coverage of the vaccine. Although we have introduced this vaccine in many countries, the number of babies actually getting the vaccine may not be optimal. There’s a lot we can do just in terms of trying to encourage more mums to take their babies to vaccinate and to get vaccines to those hard-to-reach areas. Really trying to understand what concerns moms might have around giving their babies the vaccines is important.

Are there resources such as financing to find solutions?

Resources were devoted early on to rotavirus research, especially on the African continent. It was really positive that many of the clinical rotavirus vaccine trials were done in Africa. For some other vaccines, that hasn’t happened.

There has also been investment to set up rotavirus surveillance programs in Africa which helped to show the high burden of diseases, the different types of rotavirus that are circulating, and the impact that vaccine introduction has had. The interest in this research continues today, including looking at different dosing schedules and newer vaccines.

Is that the future — newer vaccines?

There’s a drive towards development of new and better vaccines. We were involved in clinical trials here at our research unit looking at an injectable rotavirus vaccine candidate. Unfortunately, that didn’t show protection when it was assessed in a large clinical trial. We still have a lot to learn about how the body mounts an immune response to the rotavirus and the vaccines which might guide development of new vaccines and ways to assess how well they are working.

What is being considered beyond vaccines?

It’s always important to have a holistic approach. Efforts are also being made to try to prevent dehydration through oral rehydration. But in terms of preventing severe disease, vaccines really are the best intervention we have. Vaccination might not prevent the diarrhea episode totally, but it usually makes it milder. Instead of being hospitalized or dying, we now are giving those children a chance to have less severe disease or no disease at all.

The upcoming Rotavirus Symposium in Cape Town will celebrate 20 years of rotavirus vaccines. What are some of the forward-looking goals of the event?

The symposium is really a great opportunity to bring together researchers from across the world to hear about new research and create new collaborations between people working in this space. We’re also encouraging young and emerging researchers to attend. We’re looking forward to learning about some of the data and innovations that are coming out to prevent rotavirus and how we can better understand immune responses to rotavirus, because that will also help us tailor how we reach our goals of reducing that residual burden of disease.