Top Kenyan scientist shares the joys and challenges of creating life-saving vaccines

Professor George Warimwe should be a household name in Kenya. He’s a leading scientist who has created a life-saving vaccine against Rift Valley Fever. He is also leading policy-changing work on Yellow Fever vaccines. Warimwe has now been awarded the Royal Society Africa Prize for his work on vaccine development and capacity building in Africa. Moina Spooner, from The Conversation Africa, spoke to Warimwe about his life as a vaccinologist.

What types of vaccines have you helped to create?

I have a slight bias towards diseases that affect both humans and animals, so-called zoonotic diseases. This is for a few reasons. Growing up, animals were very important to my family life. We used to keep livestock, and we had a prized bull. The bull had to be sold to generate enough money for me to go to university – my education depended on that animal. The importance that animals have in people’s lives sparked my interest and I went on to study veterinary medicine. I also became interested in zoonotic diseases because humans share many infectious diseases with animals. Roughly (60%) of all human infections are acquired from animals. And of all emerging infectious diseases, over 70% are from animals or involve transmission between humans and animals.

For me, taking account of what happens in both humans and animals is really important to understand how to control diseases in both. And so I try to develop vaccines for both.

Is there a vaccine that you’re particularly proud of?

When I decided to go into vaccinology (creating vaccines) I identified Rift Valley Fever as the first disease I wanted to work on. This is because it’s a disease that was first identified in Kenya in 1930 and affects both humans and livestock (sheep, goats, cattle and camels). Rift Valley Fever is highly deadly. Over 90% of young animals die from infection. The disease can be transmitted to humans. People who work or live with these animals can catch it from them and people can also catch it from mosquitoes. It can cause severe illness in humans, and over 30% of those with severe illness die.

So, Rift Valley Fever has major implications for human and animal health. And because it’s the same virus that causes disease in humans and livestock, it’s possible to develop a single vaccine that you can use across humans and animals. We can exploit the knowledge of how immunity develops in animals to develop effective vaccines for humans and vice versa.

We knew that immunity to the disease is conferred by antibodies that bind to glycoproteins on the surface of the virus. To develop a vaccine we inserted the gene encoding these glycoproteins into a vaccine vector (a ‘vehicle’ to deliver the information into cells) called ChAdOx1. This ChAdOx1 vector has been used to make other vaccines, including the Oxford AstraZeneca COVID-19 vaccine.

When you administer the vaccine to a human or an animal, it gets into the body’s cells and directs the cells to make large amounts of the vaccine antigen (Rift Valley Fever glycoproteins) without viral replication. The body responds to this by making antibodies that can block a Rift Valley Fever virus from infecting you.

In our previous studies we showed that the vaccine – ChAdOx1 RVF – was safe and highly protective in multiple livestock species (sheep, goats, cattle) in Kenya. We’ve now started evaluating the same vaccine in humans. It’s in Phase 1 clinical trials at Oxford University with no safety concerns to date.

This has been a massive achievement, and will likely address the unmet need for a licensed human vaccine; so I’m most proud of it.

What considerations and concerns do you have when developing vaccines?

There are lots of things to think about. For instance, what immune response are you aiming to generate with the vaccine? Do you have the appropriate technology to generate the immune response? And if you do, will you be able to produce lots of the vaccine? How will it be stored? We’ve seen this with the COVID-19 pandemic. There are vaccines that can be stored at fridge temperature, and there are those that need ultra-cold storage (minus 80°C). There are vaccines that only need one dose, whereas others need several. We have to consider the logistics around this.

You also need to think of the target population of the vaccine. Will it be for adults or children? This is obviously dependent on the distribution of the disease that you are trying to make a vaccine for. For instance, if making a vaccine for use in children you need to think of how it would be deployed and whether it will need to be co-administered with other childhood vaccines.

An understanding of the nature of the immune response and clinical manifestations of the disease is also necessary, so that you know whether the vaccine provides protection or not.

These are things you have to think of very early on that play into the final cost of the product and the ease of implementing the vaccine programme. It’s like a checklist that you have to form at the start. And you try to address potential challenges – such as new variants – very early on and think of solutions.

Then you can start making your vaccine with a clear plan of how you will evaluate its safety, ability to generate an immune response, ability to provide protection, and a clear pathway for its licensing and eventual use.

What can be done to help improve vaccine development?

I have been incredibly fortunate to have excellent mentorship from global leaders in vaccinology. Added to this is the excellent research environment at the KEMRI-Wellcome Trust Research Programme in Kenya where I have been able to progress my research with input from many colleagues with diverse scientific expertise spanning immunology, social science, economics and policy.

There is lots of talent in Africa, enough to match and solve the current health challenges in the continent. To harness this we need to create a supportive research environment and associated infrastructure, provide mentorship and back this up with sustained funding opportunities. National governments in Africa have a critical role in addressing this through, among other things, funding research.

We also need to improve how much vaccine is produced in Africa. As a continent we produce less than 1% of vaccines needed; we import the rest. This has left the continent vulnerable to external forces. There is hope though. The Partnership for African Vaccine Manufacturing is developing plans to increase local production with an “ambition to manufacture 60% of Africa’s routine immunisation needs on the continent by 2040” while strengthening other components of the vaccine ecosystem.

Long-term investment in the talent in Africa will be a key success factor for our ambitions in addressing the major health challenges we face today and others that are currently brewing.

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