Livestock vaccination campaigns are often favorites of the humanitarian aid community because they engage a lot of local people, can spend large sums of money relatively quickly, and popular sentiment is that “you can’t go wrong with vaccinations, right?”
The answer, as with most things, is that you CAN go wrong with vaccinations if the specific circumstances are not carefully considered.
Mass vaccination of livestock is a potent tool in controlling and preventing diseases, safeguarding what in many societies comprises the most important single family resource. On the other hand, poorly thought-out campaigns may provide little benefit for animal owners. At worst, they can render animals even more vulnerable to disease.
A good vaccine campaign begins with a good vaccine. This means the existence of a safe, effective, inexpensive vaccine that induces rapid and long-lasting protection in the vaccinated animal, ideally with only a single injection. A long shelf-life and stability at room temperature are additional benefits. Few if any vaccines feature all of these characteristics, so there are always trade-offs to be made.
Also important for a good vaccination campaign is epidemiological information on diseases in the target area. Vaccinating against pathogens that don’t exist or that cause little harm to affected animals is asking for trouble.
Helpful disease information includes incidence and prevalence rates, clinical signs, seasonal patterns, vectors, transmission routes within and among herds, the role of wildlife, and many more.
Dependable information is difficult in the remote, infrastructure-poor areas where so many humanitarian crises emerge. Humanitarian organizations usually conduct baseline assessments that provide some epidemiological information. But in general donors are reluctant to earmark funding for in-depth epidemiological studies. And this is understandable in such crises. We must work with the tools at hand.
Fortunately, livestock owners often have sufficient observational skills to offer a good picture of what diseases are causing trouble for them. This knowledge should be taken advantage of.
Logistics are another critical factor. Many livestock vaccines used in humanitarian crises require refrigeration. Just a few minutes above 8°C (47°F) can be enough to render them useless. Even those declared as stable at “room temperature” have not been tested for extended periods at 40°C (104°F), which is common in much of the world where such campaigns are undertaken.
Refrigeration requires a cold chain, which requires a dependable energy source that is often lacking. Under such circumstances, all vaccines to be used at one time must arrive within a short period, to avoid long storage times that risk a breach in the cold chain or prolonged exposure to excessive temperatures. When hundreds of thousands of doses are involved, this is not as easy as it sounds.
In addition, a cadre of trained staff and supervisors is needed, and the ability to transport them to the target area. Unexpected rain or political instability that cut off part of the target area can mean lower percentages of herds being vaccinated. For some diseases, poor vaccine coverage can result in an increase, rather than decrease, in disease incidence (more below).
No less essential is the support of the target community. The vaccines must protect against diseases considered to be important by the livestock owners, which is best assured by having community members participate in the campaign planning. If they do not see the benefit, they will not bring their animals to be vaccinated, resulting in poor coverage.
Sufficient resources from donors and stakeholders to complete the campaign is obviously critical. Less often considered is the availability or likelihood of resources to conduct follow-up vaccinations as needed.
Many vaccines require boosters a short time after the initial vaccination in order to be effective. In some cases, constant exposure to low doses of the pathogen in the environment acts like a booster for initially vaccinated animals, and follow-up may not be urgent. But often failure to provide boosters can mean the initial vaccination campaign was wasted.
A study of the common cattle bacterial disease hemorrhagic septicemia makes this point. In areas where the disease is enzootic, vaccination was found to protect individual cattle for at least 12 months, compared to only 6 months in areas where the disease had not been present for a decade or more.
The Dangers of Vaccination
Livestock vaccination should complement good husbandry and hygiene, not replace them. Yet in most humanitarian emergencies, husbandry and hygiene are poor. Vaccinating in the face of feed shortages, or after long-distance travel to crowded water holes or refugee camps, may do little to stem disease. It can even encourage spread through the sharing of needles between multiple animals and the close contact between herds that gather for vaccination.
Ultimately, the best practice is to have regular vaccinations before disasters strike, so that emergency vaccinations – much less efficient – are unnecessary. This, of course, is not always possible.
The Importance of Vaccine Coverage
Good vaccination campaigns can be ruined by poor coverage in the target population. This can occur in many ways:
- Inability of vaccinators to access some areas;
- Unwillingness of some livestock owners to participate (for any number of both justifiable and unjustifiable reasons);
- A large number of animals unable to mount an immune response to vaccination due to exhaustion, starvation, disease, or other stresses.
A specific minimum percentage of a population must be immunized to provide optimal protection. The percentage is based on numerous factors, such as how easily a pathogen is spread, the portion of susceptible animals in a population, the presence of chronic carriers of the pathogen, whether wildlife act as hosts….
For the dreaded rinderpest virus of cattle, it was found the disease could be eradicated with vaccination of 60-80% of the cattle population. Coverage at or above this level would (and did) result in disappearance of the virus within a few years. Vaccine coverage less than 60% however was found to result in even more rinderpest disease than would have been present with no vaccination. This characteristic is not unique to rinderpest.
Follow-Up is Critical
Mass vaccinations, particularly when repeated at regular intervals, can result in near elimination of a disease in the target population. If vaccinations are then discontinued, animals born thereafter will have little exposure to that pathogen because it is so rare. If the pathogen is re-introduced into the population, these naïve animals will be extremely susceptible to the disease. If a long period has elapsed since the last vaccinations, all of the animals may be naïve. Another reason why follow-up is so important.
This may have occurred with contagious bovine pleuropneumonia (CBPP). Vaccinations for CBPP were administered alongside rinderpest to get maximum benefit from the rinderpest eradication campaign. When the latter was successful, the funding and will for continued CBPP vaccinations alone declined and the disease returned with severe clinical signs in the now naïve cattle. My point is not to criticize the amazing achievement of rinderpest eradication, only to draw attention to other lessons learned from it.
Communication is Key
Perhaps most detrimental of all is the potential for unsuccessful campaigns to cause livestock owners to lose confidence in vaccinations. Vaccinating stressed animals, after outbreaks are already well underway, or covering too small a percentage of the population, will result in many animals becoming sick despite vaccination.
In the atmosphere of humanitarian emergencies, such failures can be minimized by thorough preparation. But they cannot be completely avoided. Clear, honest communication of the risks to livestock owners is crucial to preventing loss of faith in vaccines.
Vaccination is No Panacea, but it is a Powerful Tool
As we have seen, one CAN go wrong with a vaccination campaign. I have concentrated on the negative here because in scientific circles it takes a backseat to the positive. Yet vaccination is one of the most effective tools we have to keep animals healthy. In many places, livestock are not a hobby. They are a food security and public health issue because they directly provide a large portion of the meat, milk, and eggs consumed by families. Keeping them healthy is critical.
But before any vaccination campaign begins, some basic questions must be answered:
- Is vaccination really needed?
- Is the target disease(s) truly a priority and recognized as such by livestock owners? Or is it chosen because the vaccine is easily accessible and “it can’t hurt, right?”
- In a nutshell, is the potential good provided by vaccination much higher than the potential harm, given the circumstances?
Vaccination campaigns look great on paper, and often provide a huge service to communities. But if the answers to these questions are not clearly positive, some rethinking is needed.
Catley A, Abebe D, et al. Impact of drought-related vaccination on livestock mortality in pastoralist areas of Ethiopia (2009). Overseas Development Institute: Oxford.
De Alwis MCL. Haemorrhagic Septicaemia (1999). ACIAR Monograph No. 57: Canberra.
Grandon S, Mackinoon M, et al. Imperfect vaccination: some epidemiological and evolutionary consequences. Proc. R. Soc. Lond. B. 2003; 270: 1129-1136.
Lubroth J, Rweyemamu MM, et al. Veterinary vaccines and their use in developing countries. Rev. sci. tech. Off. Int. Epiz., 2007; 26(1): 179-201.