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Chris Victor

Chris Victor is leading a study of influenza vaccine in tropical Africa. Photo: PATH/Patrick McKern.

Will influenza vaccines work in tropical developing countries?

People in Senegal definitely get influenza, but does the tropical country have a flu season? Or does the virus circulate year-round? Will the vaccine made for the United States and Europe protect children in Senegal from the flu?

“In the US we’ve had decades to study influenza and influenza vaccines in our population,” says John (Chris) Victor, advisor for epidemiologic science and clinical trials for PATH’s Vaccine Development Program. “But you can literally count on one hand the number of influenza vaccine studies conducted in tropical Africa.”

How will vaccines work?

Chris is leading a large-scale effectiveness trial of a killed influenza vaccine in Senegal to study how well the vaccine will protect children in sub-Saharan Africa. The vaccine already is proven safe and effective for children in the United States and similarly developed countries and has been approved for use around the world. But its use in Senegal has been limited because of questions about need, effectiveness, feasibility, and cost.

“Until recently, influenza has not really been on the table as a problem for tropical developing countries.”

Chris's study is generating data that will help public health officials understand the vaccine’s potential impact on influenza disease burden and related deaths in tropical Africa, including deaths from pneumonia—the leading cause of death among children under age 5 worldwide. Studies in other African countries have found influenza is associated with up to one-quarter of all severe childhood pneumonia cases. The study data may help health leaders decide how best to use influenza vaccines in Senegal and other tropical countries in the future.

PATH and our partners, including the Institut de Recherche pour le Développement (IRD) and Senegal’s Institut Pasteur de Dakar, are evaluating the vaccine among 20 villages with nearly 36,000 people. In 2011, more than 9,400 children ages six months to ten years were vaccinated. Half of them received the influenza vaccine, while the other half received inactivated polio vaccine. That way, researchers can compare influenza rates among the two groups while still providing a benefit to the participating children. Local investigators are monitoring the effectiveness of the influenza vaccine by conducting intensive surveillance for influenza and severe pneumonia.

The study is funded through a cooperative agreement with the Influenza Division at the US Centers for Disease Control and Prevention (CDC).

A need for data

Chris discusses the clinical trial:

Yearly influenza vaccination may be relatively expensive for developing countries. So countries aren’t going to start vaccinating large numbers of their populations unless we understand better what is the benefit and impact of vaccination.

Influenza vaccines, especially newer ones, have the potential not only to elicit protection against influenza strains that are contained in the vaccine, but also to provide some protection against strains that are not in the vaccine. The duration of protection may also be longer than one year. However, until we have a universal influenza vaccine that produces broad long-term protection, we need to develop influenza vaccination strategies that give developing countries the most bang for the buck.

Until recently, influenza has not really been on the table as a major problem for tropical developing countries. It’s just in the last few years that it’s really being looked at in terms of its contribution to childhood pneumonia deaths and to maternal mortality. But there’s a lot of work to do yet. If much of influenza-related mortality is among vulnerable young children who are dying from influenza-related pneumonia, one strategy may be to vaccinate infants and young children for a few years early in their lives when they’re most vulnerable. Then maybe we’ll have a big public health impact on childhood survival by getting them through those vulnerable years.

The importance of a mother

Chris describes how vaccinating mothers can help protect their children:

Maternal vaccination may be another critically important way to begin to address influenza-related mortality in the developing world. We know that pregnant women are at an increased risk of serious outcome with influenza. Moreover, there’s growing evidence that antibodies passed to the developing fetus by vaccinating the pregnant mother can protect the infant against influenza after it’s born and until it’s old enough to receive influenza vaccine. So one influenza vaccine, given to the mother, can protect two people—mother and child.

All this said, you can’t answer questions about the effectiveness of influenza vaccination unless you have information about influenza in these populations. The World Health Organization (WHO) and CDC have contributed a tremendous amount in terms of expert support and financial resources to developing countries to build and strengthen influenza surveillance and research capacity. A few years ago, most countries in Africa had little capacity for influenza surveillance in their populations. Now, there are at least two dozen African countries regularly participating in WHO and CDC influenza surveillance and research activities.

Benefits for future projects

Strengthening capacity and building on existing work in the course of research can benefit both current and future projects, Chris says:

An important aspect about how we work at PATH is that we also try to strengthen capacity and build on existing partnerships. We didn’t just go into Senegal with this influenza project and start at ground zero.

The Meningitis Vaccine Project [a partnership between PATH and WHO] had a very successful relationship with IRD in Senegal and worked with them to conduct clinical studies of the new MenAfriVac® vaccine developed specifically for Africa. Our partnership with IRD is built on their strength locally in Senegal as much as our expertise in vaccine development. Additionally, the influenza laboratory at the Institut Pasteur de Dakar has been one of the strongest national influenza centers in Africa, and we’re supporting their continued development and role as a leader in West Africa.

So, we hope we’re strengthening our partners in a way that benefits not only PATH’s particular influenza study, but also potentially benefits other projects and researchers in the future. We want to see investments in research in Africa like ours continue to grow into a tradition that benefits these populations long into the future.

MenAfriVac is a registered trademark of Serum Institute of India Ltd.

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