Vet on call: Don’t ignore vaccines despite reaction risks

My article of November 2 caught the interest of various parties. I discussed cattle that reacted adversely when I vaccinated them against foot and mouth disease.

The vaccine manufacturer, Kenya Veterinary Vaccines Production Institute (KEVEVAPI), called to know whether I had directly purchased the product from their office or authorised agents and they also requested for vaccine container.

The Veterinary Medicines Directorate (VMD) also requested for a full report on the issue. VMD is a fairly new institution under the State Department of Livestock in the Ministry of Agriculture, Livestock, Fisheries and Irrigation.

It was established in 2015 as the national regulator of animal health inputs.

The prompt reaction from the two national institutions is encouraging because it means that they are alert and ready to engage in matters related to livestock health.

Other responses came from livestock farmers from different parts of the country. They fell into three groups. The first one wanted to understand why we, veterinary experts, use vaccines that we are aware may cause adverse effects on animals.

The second group wanted to know if they would be compensated if their animals die from use of licensed vaccines.

Finally, there were those who wanted to know how many vaccines cattle should be given and why diseases like foot and mouth (FMD) keep recurring despite vaccination.

The answer to the first question lies in the principle of cost-benefit analysis. It simply states that when benefits of an intervention are much greater than the cost, then it is appropriate to implement the intervention even though there may be some undesirable outcomes.

Most medicine products have the potential to cause some adverse effects on the patient. Nonetheless, if only a very small proportion of the patients will show adverse effects while the rest will be treated or prevented from getting the disease, then the drug is deemed appropriate for use.

Vaccines are some of the safest medical products used in both human and animal health because majority of them are developed from killed microorganisms. These are called the killed vaccines.

Others are made from micro-organisms that have been treated in a way that keeps the germs alive but removes their ability to cause disease.

ADVANCEMENT OF VACCINOLOGY

These are known as attenuated vaccines. When attenuated vaccines are injected into the animal, the micro-organisms multiply without causing disease.

The body responds by producing antibodies that kill off the germs and leave the body with a memory of the disease. If the body is exposed to the disease in future, it quickly produces antibodies and fights off the infection. Unfortunately, there is still a small risk that the organisms could regain their ability to cause disease.

There are also vaccines that use parts of a micro-organism to stimulate the patient’s immunity. These are called subunit vaccines.

They are safer than both the killed and attenuated vaccines. They have a big potential in the advancement of vaccinology in both humans and animals.

Finally, there is the infection and treatment method like in vaccination against East Coast Fever (ECF) in cattle. The micro-organism is injected into the animal in small doses that are known to be killed by the tetracycline antibiotic.

The animal reacts with a rise in body temperature. An antibiotic injection is given before the ECF parasites multiply a lot and enter the bloodstream.

The treatment kills the parasites but the body produces sufficient immunity to protect the animal from future infections.

In all these vaccination products and methods, the experts know there is a risk of reaction to the microbial proteins or the chemicals used in vaccine production and delivery.

There could also be infection. However, the level of protection the vaccine gives and the known impacts of the disease it prevents far outweigh the risks of patient adverse reaction.

Most vaccines should be able to protect at least 80 per cent of vaccinated animals and have few or no animals reacting to the carrier substances.

In exceptional cases of very severe diseases like African swine fever, a lower protection level could be acceptable while planning to keep researching on improvement of the vaccine.

I advise farmers to insure their animals against accidental death because compensation may only be possible if the manufacturer is found to have sold a substandard or adulterated product.

ONCE IN THEIR LIFETIME

You see, the manufacturer would not be able to determine whose animals are likely to react and die. Fortunately, most vaccine reactions are allergic in nature and are readily treated with antihistamines, adrenalin and corticosteroids.

For the last group of responses, let me first deal with FMD recurrence despite vaccinations. The main reason why we still have FMD in Kenya is because we vaccinate by the infamous knee-jack reaction. Most farmers, public and private service providers vaccinate cattle when there is an FMD outbreak or threat of one.

In a country like ours where the FMD virus lives in the environment, the country needs to have a diligent national programme of vaccination and disease surveillance for many years to stamp out the virus.

We are unlikely to completely eliminate FMD unless our neighbouring countries also have similar programmes, but we can keep our herds free of the disease by sustained vaccination.

Currently, farmers should vaccinate their cattle every six months against FMD even if no disease has been reported in their area.

In addition to FMD, farmers in Kenya should routinely vaccinate their cattle against lumpy skin disease, black quarter and anthrax (Blanthrax).

Other diseases include Rift Valley fever (RVF), enterotoxaemia in calves, contagious bovine pleuropneumonia (CBPP) and ECF.

Virgin heifers should be given brucellosis vaccines once in their lifetime but the vaccine is not recommended for mated cattle.

Cows can also be vaccinated against bovine haemorrhagic septicaemia, a disease that spreads fast in the herd. There are some commercial vaccines available for limited protection against mastitis but they lack a clear demonstration of economic benefit.