Value of Vaccination

A greatest gamble of Edward Jenner in 1796 by inoculating his 13 year-old-son with vaccinia virus (cowpox), to demonstrate immunity to smallpox was prompted by observation that milkers and their families failed to contract Small Pox. The gamble paid and gave birth to Vaccines. In 1798, the first smallpox vaccine was developed.

Over the 18th and 19th centuries, systematic implementation of mass smallpox immunisation culminated in its global eradication in 1979. Louis Pasteur’s experiments spearheaded the development of live attenuated cholera vaccine and inactivated anthrax vaccine for humans in 1897 and 1904, respectively.

Plague vaccine was also invented in the late 19th Century. Between 1890 and 1950, bacterial vaccine development proliferated, including the Bacillis-Calmette-Guerin (BCG) vaccination, which is still in use today. In 1923, Alexander Glenny perfected a method to inactivate tetanus toxin with formaldehyde.

The same method was used to develop a vaccine against diphtheria in 1926. Viral tissue culture methods developed from 1950-1985, and led to the advent of the Salk (inactivated) polio vaccine and the Sabin (live attenuated oral) polio vaccine. Mass polio immunisation has now eradicated the disease from many regions around the world.

Animals receive vaccines for the same reason that humans do: to prevent diseases. Vaccinating animals reduces animal suffering, reduces the transmission of microorganisms in the animal population, and is often more affordable than paying for the treatment of sick animals. 

Pets receive vaccines for infectious diseases such as rabies, parvovirus, distemper, and hepatitis. Domestic animals are vaccinated to prevent diseases like FMD, Anthrax, Black Quarter, Hemorrhagic Septicemia, Rabbies etc and so do the Poultry birds against Mareks, Ranikhet and Infectious Bursal disease etc. Vaccinations keep individual animals, flocks and herds, and people healthy.

World Veterinary Day celebrated throughout the world on last Saturday of April to highlight the role of Veterinarians has a specific theme every year. This year the theme of World Veterinary Day is Value of Vaccination.

The major goals of veterinary vaccines is to improve the health and welfare of companion animals, increase production of livestock in a cost-effective manner, and prevent animal-to-human transmission from both domestic animals and wildlife.

These diverse aims have led to different approaches to the development of veterinary vaccines from crude but effective whole-pathogen preparations to molecularly defined subunit vaccines, genetically engineered organisms or chimeras, vectored antigen formulations, and naked DNA injections. Veterinary vaccines have been produced successfully against viral, bacterial, protozoal, and multicellular pathogens.

These have, a major impact not only on animal health and production but also on human health through increasing safe food supplies and preventing animal-to-human transmission of infectious diseases.

The continued interaction between animals and human researchers and health professionals will be of major importance for adapting new technologies, providing animal models of disease, and confronting new and emerging infectious diseases.

In its original concept, vaccination aims to mimic the development of naturally acquired immunity by inoculation of nonpathogenic but still immunogenic components of the pathogen in question, or closely related organisms.

The criteria for successful animal or veterinary vaccines can be very different from those for human vaccines depending on the animal groups under consideration.

For example, criteria for companion animal vaccines are similar to those for human vaccines in that the health and welfare of the individual animal are primary concerns.

The main objective of livestock vaccines, on the other hand, is to improve overall production for the primary producers, and the cost-benefit resulting from vaccination is the bottom line for this industry.

Vaccination against zoonotic or food-borne infections is aimed at reducing or eliminating the risk for the consumer and in some cases to improve the productivity of the individual animal. Vaccination of wildlife is generally considered only with respect to infections that are transmittable to humans (zoonotic diseases), although welfare concerns are of increasing importance.

Animal Vaccine sector has grown consistently mainly due to new technological advances in vaccine development, the continuous development of drug resistance by pathogens, and the emergence of new diseases.

Apart from improving animal health and productivity, veterinary vaccines have a significant impact on public health through reductions in the use of veterinary pharmaceuticals and hormones and their residues in the human food chain. In addition, vaccines contribute to the well-being of livestock and companion animals, and their use is favored by the growing animal welfare activists.

Types of Vaccines

There are 4 main types of vaccines:

Live-attenuated vaccines

Inactivated vaccines

Subunit, recombinant, polysaccharide, and conjugate vaccines

Toxoid vaccines

Difference between Live and Killed vaccine

LIVE VACCINE KILLED VACCINE

1              Live vaccine is prepared from living disease causing organism which are attenuated and bears antigenic and immunogenic character and are non pathogenic or less pathogenic They are prepared from disease causing micro-organisms which are killed or inactivated by physical or chemical agents which render them non pathogenic but their antigenic and immunogenic character is maintained

2              Live vaccines produce immunity by multiplication of organism present in vaccine inside the body of host Organisms cannot multiply so amount of antigenic mass injected into the body will produce antibody.

3              Less quantity of antigenic mass is required to develop active immunity Large quantity of antigenic mass  in comparison to live vaccine is required to develop immunity

4              The immunity produced by live vaccine lasts for longer period in comparison to killed vaccine Immunity will not last long unless suitable adjutants are added

5              Live vaccine is used when disease is endemic and regularly occurring Killed vaccine is used in areas where there is a chance of entering of disease or in case live vaccine is not available

6              Animals vaccinated with live vaccine can become carrier of the disease so live vaccine is used to control the disease Animals cannot become carrier. This vaccine is preferred in eradication campaign of the disease

7              Live vaccine is administered locally or parentrally Only administered parenterally

8              Stored under refrigeration Stable at room temperature

9              Animalss vaccinated with live vaccine may develop clinical symptoms of the disease which may spread to other susceptible birds. Animalss vaccinated with killed vaccine do not develop clinical symptoms but sometimes local reactions at injection site may develop due to the effect of adjuvant.

10           Live vaccines may be contaminated with other organisms that are transmitted through contaminated embryos and cell cultures etc. There is no chance of such contamination

11           Live vaccines are mostly available in freeze dried form and has to be reconstituted or diluted with suitable diluents Killed vaccines are available in liquid form to be used as such after proper shaking. No need of reconstitution.

12           Vaccine virus may be excreted from vaccinated flock and can be transmitted to susceptible birds in contact Vaccine virus is not excreted

Vaccine failure

Under certain circumstances there is poor antibody production after vaccination. This results in outbreak in vaccinated flock. The vaccine failure may be due to

•             Problem with vaccine

•             Improper attenuation

•             Proper strain not used

•             Use of infected glassware, syringe, needles etc

•             Improper site of vaccination

•             Administration of less or more vaccine

•             Use of some disinfectant/antiseptic/antibodies at the time of vaccination

•             Some individuals may escape vaccination and become source of outbreak

•             Problem with host like high antibody titer or animals under stress

Factors affecting vaccination

Type of vaccine used : Sometimes vaccines themselves are the cause of vaccination failure. Vaccines of standard company should be used. If some problem arises enquire from the others using same batch of vaccine. For this purpose keep a record of the brand, batch number etc.

Vaccine administration: Proper dose, proper timing, proper route, proper diluents and proper needles, syringes etc and maintenance of cold chain

Emergence of new strain of viruses and bacteria: New strains of bacteria and viruses and continuously emerging that may not be included in the vaccine

Maternal antibody levels: Presence of maternal antibodies is the greatest factor in reducing vaccine effectiveness. There is no easy solution to overcome this problem because resistance takes time to build up immunity against certain disease is inherited by young as antibodies from the mother. This maternal or passive immunity is replaced by antibodies by individual but if vaccine is used before maternal antibodies have declined they may fight off new vaccine and neutralize it.

Health status of Flock: Vaccination should be done on healthy flock only. Postpone vaccination in event of any disease or debility. Never perform vaccination during outbreak of a disease against which immunity is sought.

Nutrition : Malnutrition especially deficiency of protein in ration and high concentration of aflatoxins reduces response to a particular vaccine. As far as possible animalss should be built up for vaccination by providing extra vitamins and minerals.

General Precaution during Vaccination

Vaccinate apparently healthy animals, housed in clean environment. In case of sickness postpone vaccination

Handle animals gently

Vaccinate in cool hours of the day

Avoid over crowding

Administer anti-stress medicine after vaccination. Use of vitamins particularly vitamin A&E is quite helpful.

Maintain cold chain. Store vaccine at 4oC

Use before expiry date and keep a record of all vaccinations, including batch no, brand, manufacturer etc. Better to stick a label on vaccine bottle to the record book.

Prepare vaccine in suitable diluents, preferably one supplied by the manufacturer.

Use sterile glassware, syringe, needles, vaccine guns etc.

Never use antiseptics/disinfectants etc at time of vaccination.

Provide 1 week interval between two vaccinations.

In case of vaccines failure give immuno-stimulants, vitamins A&E, Selenium preparations, probiotics etc.

Use reconstituted vaccine within 2 hours. While vaccinating a large flock do not reconstitute vaccine at once. Reconstitute in batches.

Destroy left over vaccine, empty vials, needles etc by burning. Use right dose and right dilution and vaccinate at right age.

Avoid hiring a vaccinator who vaccinates other flocks also. Vaccinator should follow biosecurity measures strictly.

Author is a Veterinarian who works as Professor cum Chief Scientist at FVSc & AH, SKUAST-K, Shuhama, Alusteng Srinagar.