Vaccines – What are They and How do they Work?

Vaccines play a vital role in preventing disease and protecting animal health and welfare. Just as when we are unwell we don’t perform to our best, so it is with livestock; keeping cattle healthy helps improve productivity!

In keeping cattle healthy, vaccines also help reduce our requirement for antibiotic treatments. As such increased use of vaccines is one of the recommendations made by the RUMA* task force (and one they are measuring) to reduce antibiotic use in cattle. A recommendation which recognises that reducing antibiotic use should not be at the expense of the health and welfare of animals under our care.

Vaccines are therefore indisputably an important tool in our armoury to protect our livestock against important pathogens and diseases, so I want to look at vaccines more generally in terms of what they are, how they work, and some general considerations for their use. Vaccines are an investment in your herd’s health; understanding what they are and how they work will help ensure you maximise the benefit from them.

What are vaccines?

Vaccines are medicines which are designed to stimulate the immune system. Animals can be vaccinated against particular viruses, bacteria or parasites so that when they encounter these pathogens for real they are more able to fight off the infection. Vaccines can be either live or inactivated.

live vaccines

How Do Vaccines work?

Vaccines work by exposing the animal’s immune system to the particular virus, bacteria or parasite in a safe way. This can have 2 functions;

1. Enhanced resistance to disease: The immune system of a vaccinated animal is primed to be able to neutralise the pathogen it has been vaccinated against more quickly. If the vaccinated animal comes into contact with any of the pathogens it has been vaccinated against in later life, the immune system is able to respond more quickly and more specifically so it is less likely to get sick.

2. Reducing viral and bacterial exposure: Sick or infected animals will shed large quantities of the virus or bacteria they are infected with.  For example, youngstock with pneumonia will shed pathogens in secretions from the eyes and nose, and in exhaled air, which can go on to infect neighbouring animals. Vaccination reduces both the number of sick/infected animals and the amount of virus or bacteria they shed, so reducing the amount of virus and bacteria in the air and reducing the risk of neighbouring animals (both those in contact, and those sharing the same airspace) becoming infected. It’s important as well to remember that animals can become infected and not show clinical signs. These animals are less likely to be treated, and therefore continue to infect other animals around them. Vaccination is a group or herd strategy so ensuring the immunity of the whole group is improved, and that the whole group are shedding less pathogens.

vaccinated vs non vaccinated

Key Considerations For Youngstock Vaccine Selection

When selecting and undertaking any vaccination programme there are a number of things to consider. Using vaccination against calf pneumonia as an example; 

1. Ensure cover against the likely pathogens for the full risk period

Vaccines should be used which protect against the viruses/bacteria present on your farm for a sufficient period of time to see them through the main risk period (e.g. the winter housing period).

2. Ensure protection is in place BEFORE challenge

For dairy/dairy-bred calves, late autumn/winter born suckler calves, and bought-in animals this can be difficult. Vaccines do not work immediately, for example pneumonia vaccines requiring a 2 dose course may not give protection until 5-6 weeks after the first dose. In these situations single dose vaccines, delivered via the intranasal route may be more appropriate.

3. Vaccinate ALL animals in the group

Vaccination is in most instances a HERD/GROUP strategy (remember that the role of vaccination is 2 fold; increase immunity, and reduce pathogen shedding) - the best results are therefore gained from vaccinating the whole group within for example an airspace or management group. If an active decision has been taken not to vaccinate a particular group of calves, ideally these animals should be managed separately; in the case of pneumonia vaccination this means a separate airspace.

4. Consider the age of the animal: passive immunity (from colostrum) can interfere with vaccination in young calves

Ensuring calves receive adequate colostrum is a vital part of overall calf management, but antibodies absorbed from this colostrum can prevent some vaccines from working. Intranasal vaccines can help to overcome this issue.

5. Avoid stress

Where possible avoid vaccinating at the same time as stressful procedures such as dehorning, castrating and weaning. The calf needs to ‘respond to’ the vaccine and stress can reduce its ability to do this, preventing the vaccine from working effectively. Your vet is best placed to discuss with you when is the most appropriate time to vaccinate the animals on your farm, as this will include practical considerations including fitting vaccination in alongside other management procedures.

Vaccines are a highly effective way of protecting animals against disease; understanding how they work helps ensure we use them properly and get the most benefit from them.

*RUMA – Responsible Use of Medicines Alliance

Further information can be obtained from your vet or the product SPC or from Zoetis UK Ltd, 5th Floor, 6 St. Andrew Street, London, EC4A 3AE • Customer support 0845 300 8034 • • Use medicines responsibly (• Produced June 2019 • MM-05728