Foot-and-mouth-disease is one of the world's most contagious and economically damaging diseases. Infected animals develop lesions on the feet, mouth, and/or mammary glands which cause lameness, loss of appetite and decreased milk yields.
Though mortality rates are low, it threatens the productivity of animal systems around the world. The economic losses can reach US$ 9 billion, as seen by modern outbreaks in the UK.
My research focuses on how Tanzanian households manage foot-and-mouth disease in cattle. Foot-and-mouth disease is endemic in the country and over 50% of the population keep livestock for economic and nutritional security.
Foot-and-mouth disease has had devastating effects. For example, it has led to a decrease of 67% in milk yields and 27% less cash from livestock sales in parts of Tanzania.
Despite these effects, and the risk of experiencing up to three outbreaks a year, few households choose to vaccinate against the disease.
My colleagues and I found that this is a rational decision in which households have weighed the costs and benefits and decided against it.
The reasons for not vaccinating
In addition, the cost of the vaccine coupled with production losses from a failed vaccine can outweigh the potential gains.
Livestock-dependent households have to balance competing responsibilities between immediate - direct human health or food - needs with investments in livestock for long-term returns.
We surveyed 489 households to assess what determines their preference for a routine vaccination plan (every six months), and an emergency vaccination option (applied during an outbreak).
We found that most households were willing to pay for both options. However, they were willing to pay more for an emergency vaccine. The logic here was that an emergency vaccine addressed a more immediate risk.
The responses imply that households will be more inclined to vaccinate during times of need and if they have more resources available.
Foot-and mouth-disease is highly contagious. When one animal becomes infected, the chances of the entire herd becoming infected are high. While households will pay more for an emergency vaccine, there is a greater risk to vaccinating during an outbreak as the foot-and-mouth virus is highly contagious making the chances that an animal has already been infected high.
This increases uncertainty whether the vaccination will work - and uncertainty underlies the decision making process. It is why, even though they may not know the reason the vaccine didn't work, some people choose not to vaccinate their animals.
There are good reasons for this scepticism. Foot-and-mouth disease vaccines have successfully helped to control the disease in several parts of the world, among them South America. But in Tanzania, the presence of four of the seven serotypes (strains of the virus) complicates the picture. Households reported past vaccines to be ineffective in preventing symptoms. This aligns with knowledge that vaccines have traditionally been produced outside of the country and may fail to match the circulating serotypes and strains.
In combination with other research in the area, we suggest targeted vaccination with high-quality vaccines to be a best practice. Livestock-dependent households accurately identify risk and want vaccines but need additional assurance of the vaccine's quality.
With an improved understanding of the behaviour of the virus in Tanzania, we are closer to improving the odds of providing the vaccine matched to the circulating virus. Households, that are far enough not to have been affected by an outbreak, can then vaccinate.
With this information, we need to ensure the proper delivery of the appropriate vaccines. And the benefits of vaccination need to be promoted through informal, social connections, or trusted professionals in target communities. This will help align people's perceptions of risk more closely with public health objectives for population immunity.
Without these additional interactions, we will fail to connect a households's cost-benefit calculations with the control strategies necessary to reduce the burden of disease.