April 3, 2012 | The Editors

Disease under surveillance

In 2009, the government of The Gambia introduced a vaccine against pneumococcal disease, the most common cause of pneumonia. Since pneumonia is the leading killer of young children, the wisdom of immunizing them against its causes would seem to be a foregone conclusion. But science—and children—require proof.

Smiling woman in black and white top.
Dr. Effua Usuf. Photo: PATH/Patrick McKern.

That’s where Dr. Effua Usuf and disease surveillance come in. Dr. Usuf, a native of The Gambia, is a research partner in a special study sponsored by the GAVI Alliance’s Accelerated Vaccine Introduction initiative, of which PATH is a partner. Dr. Usuf and her colleagues are using disease surveillance to help determine the effect of introducing the vaccine in The Gambia. Dr. Usuf visited our Seattle headquarters recently and explained the importance of disease surveillance.

Q: What is disease surveillance?

A: When we talk about disease surveillance, we’re talking about keeping watch. We’re looking out for disease in the community. It helps you to understand who gets the disease, and if you know who gets the disease, then you know how to help them better.

Q: Why is surveillance so important in The Gambia?

A: The vaccine is the best that we’ve got right now, but it’s kind of limited. Pneumococcus (a type of bacteria that causes pnuemococcal disease) has more than 90 serotypes. The first vaccine we introduced protected against only 7 serotypes—the main ones that cause disease. Since then we’ve moved on to a vaccine that covers 13 serotypes.

So, these are good. But we realize that they are limited, and there have been issues—would we have replacement disease? Let me explain that: you’re targeting bugs that are part of a very big family. So if you take out some of the bugs, the others might come in and take the opportunity to cause disease. That’s why it’s so important to do surveillance in this case.

Q: How did you go about setting up the surveillance program?

A: Most of the time you can just do hospital-based surveillance. But the issue with that is you’re only covering people who come to that hospital. You may not know what is actually happening out in the community. So we did community-based surveillance. We have satellite clinics, and we catch the people who come to the satellite clinics. We hope that what we are seeing is a true reflection of what is happening out in the community.

Q: You also had people going to every household in more than 200 villages every four months, right?

A: Yes. That helps us understand our population: how many people are coming in, how many people are going out. It’s part of our demographic surveillance system that really gives us a denominator for our numbers, for example, the total number of children under five in our community.

Q: You don’t have detailed results yet, but what do you hope to find out?

A: We are looking for the effectiveness of the vaccine. I talked about the serotypes—the bugs that are covered by the vaccine. Are we seeing less of those diseases in the community? That’s what we’re looking for: is the vaccine working?

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