Edward Jenner, an English scientist, developed and introduced the first successful vaccine in 1796. He made cows to gift humans a lasting solution to smallpox.
The disease was a global menace that severely affected large human populations with devastating consequences of death, desperation, blindness and lifetime scars.
Edward observed that milkmaids infected with cowpox became resistant to smallpox infection. Cowpox in both humans and cattle is a mild viral disease that only causes blisters on the affected parts of the skin and they later heal without leaving any marks.
Jenner went further and demonstrated that when people were inoculated with the cowpox virus, they would not get smallpox when they were challenged with its virus. He termed that process of protection “vaccination” from “vacca”, the latin word for cow. Vaccination may, therefore, be loosely translated as “cownisation”.
The cowpox-smallpox beneficial link led to heightened vaccine production and mass human vaccination globally. In 1980, the World Health Organisation (WHO) declared smallpox eradicated globally.
Since Jenner’s discovery, medical scientists in human and veterinary medicine have developed many vaccines against disease-causing bacteria, viruses and protozoan parasites.
The world again in 2011 declared the deadly rinderpest viral disease that affected mainly cattle eradicated.
These are the only two diseases in the world that have been eradicated by active vaccination, surveillance and education. Many others may eventually follow.
A disease is considered eradicated when it stops circulating in the global population. Elimination, on the other hand, refers to stopping the disease from circulating in specific populations.
One question I keep encountering from farmers is whether vaccines are absolutely safe. Now, unfortunately, the answer is no.
CASE OF ADVERSE REACTION
However, we use vaccines in both humans and animals by taking into account their scientifically determined level of protection against a disease, the frequency of occurrence of adverse reactions and severity of the reactions in the patients.
I had my day with undesirable vaccine reactions last week in Murang’a. My colleague, Dr Veronica, and I had gone to vaccinate sheep, goats and cattle on a farm against foot and mouth disease.
The vaccine is given twice per year and protects the animals well. The farm manager, Joshua, who is also a paravet, participated in the exercise.
We dewormed the animals at the same time. There is no known adverse reaction between the vaccine and the dewormer we were using. We had just completed the vaccination when Joshua drew my attention to a 15-month-old heifer.
The animal was raising and shaking its head. It was producing a lot of saliva and kicking objects. It would also kick the underside of its belly repeatedly and kept attempting to urinate without yielding anything.
The heifer further deteriorated within a short time to staggering and having a high-stepping gait. It was getting into severe breathing difficulties. I quickly decided this was a case of adverse reaction to the vaccine or the dewormer. The heifer had been given both.
Well, the cause did not matter. We needed to quickly arrest the situation or we could lose the valuable animal to an allergic reaction, medically called anaphylactic shock.
I instructed Veronica to quickly inject the heifer with antihistamine deep into the neck muscle and keep adrenaline injection ready in case we needed to use it.
Before she could draw the medicine from the bottle, I noticed a bull in the same pen had started having round raised swellings on the skin of the neck. It also kept passing small quantities of urine. In addition, the hairs were standing on end.
“Another adverse reactor,” I exclaimed. I shouted to Veronica to bring the whole bottle of antihistamine and several needles and syringes. I could not tell how many more animals were going to surprise us with the allergic reaction.
In the whole of my practice life, I had never seen cattle reacting adversely to foot and mouth disease vaccine. I have vaccinated thousands of animals uneventfully but here was my waterloo.
The five minutes Dr Veronica took to bring the allergy antidote looked like a lifetime. The heifer would sometimes appear to be going down on its knees, then raise its head up and jump to its feet. I feared it would collapse and die.
I injected the bull as my colleague attended to the heifer. I quickly scanned the other 20 animals that we had been vaccinated and fortunately all appeared well.
Within the first five minutes of injection, the two reactors started showing signs of recovery. I concluded adrenaline injection would not be necessary.
We were still observing the reactors when one of the workers I had asked to watch over the calves came running and reported one of them had started reacting.
We rushed to the calf pens. The calf’s eyes were almost swollen shut and had copious amounts of a clear discharge.
The heifer’s vulva was swollen and partially showing a heavily reddened internal surface. The calf reacted violently to my touch. This is medically called hyperaesthesia. Occasionally, the calf would go down on its knees then rise up.
I gave the calf a high dose of the antihistamine deep in the neck muscle and a smaller dose under the skin. The reaction here was much more serious than with the older heifer and the bull. We had vaccinated the calf for the first time while the heifer and bull were in their third vaccination from birth.
I stayed on the farm until the reactors had all recovered and were behaving normally again. It took about one hour for them to regain. No other animal has shown adverse effects since then.
Such adverse vaccine reactions occur in animals in very small proportions of the population. It is estimated to be about one reactor in a million doses of a high quality vaccine.
Animals can react to microorganism proteins in the vaccine, protein or non-protein components of the vaccine product.
The following day, I prepared a report of the vaccine adverse reaction and shared it with the manufacturer. This helps in monitoring product performance and documenting adverse reactions.