Vaccines: how and when are they given?
Rob Reddick explores how vaccines are designed to work most effectively in the body
How are vaccines given?
Vaccines generate immunity across the body as a whole, but they can also provoke specific immune responses in specific bodily areas. For this reason, the varying delivery methods of vaccines are important.
Vaccines are most effective if they can stimulate the creation of antibodies where pathogens are likely to invade and harm the body, for instance in mucous membranes. So, to ensure that their action is suitably targeted, the delivery routes of vaccines often mimic the invasion routes of pathogens.
For example, the oral polio vaccine is ingested in order to stimulate the creation of antibodies in the lining of the intestines, as this is where the poliovirus ends up and multiplies after entering the body in contaminated food and water. The oral cholera vaccine generates one localised set of antibodies that stop Vibrio cholerae bacteria from attaching themselves to the intestinal wall, and another set that prevents the bacteria’s toxins from binding to the intestine’s mucous membrane.
Intranasal (up-the-nose) delivery of vaccines achieves the same effect, but in the mucous membrane of the nasal cavity. This delivery method is used to combat diseases that need to overcome the nasal mucous barrier in order to infect the body, such as influenza.
However, specific delivery routes are also sometimes necessary to minimise the chances of vaccines having adverse effects on the body. Vaccines containing aluminium-based adjuvants often cause inflammation (granulomas) unless they are injected into muscle tissue. The BCG (Bacille Calmette–Guérin) vaccine for tuberculosis is injected into the topmost layer of the skin – a process known as intradermal injection – to avoid it causing damage to blood vessels and nerves.
Some vaccines – such as those for yellow fever and MMR (measles, mumps and rubella) – work best when released slowly into the body. For this reason they are injected into the layer of fat between the skin and muscle. The limited blood flow in this area prevents the vaccine from being distributed around the body too quickly. This method is known as subcutaneous injection.
Why do we have different vaccines at different ages?
Vaccines are given to people when they are at risk of contracting a disease. Many vaccines are given at a young age because children’s bodies may not be strong enough to fight off naturally occurring diseases, which puts them at risk. Measles, for example, killed 122,000 people globally in 2012, and is one of the leading causes of death among young children – this is why children are given a measles vaccination at an early age.
Some vaccines are given to children because they work less effectively in adults. For example, when immunising those at risk of contracting tuberculosis, the NHS recommends giving the BCG before the age of 16, and never past 35 – at this age it simply isn’t effective in stimulating an immune response.
However, some diseases become a risk only later in life and so childhood vaccination is not needed. Human papillomavirus (HPV), which can cause cervical cancer, is transferred through sexual contact, so the HPV vaccine is commonly given to girls only once they have reached puberty. (See our cervical cancer case study for more.)
Likewise, before the age of 65 most adults aren’t at risk of becoming seriously ill from influenza. However, as the body ages, its ability to fight flu decreases. Because of this, anyone over the age of 65 in the UK is entitled to a free annual flu vaccination, to protect against strains of the disease from recent years.
Differences and changes in risk explain why vaccine programmes vary from region to region and over time. For example, in the UK the BCG is only offered to children who live in an area where contracting tuberculosis is a real risk, such as inner-city London; children in low-risk areas do not receive the vaccine. For diseases that have been eradicated, such as smallpox, vaccination programmes no longer exist.
Why and how are vaccines kept cold?
The antigens in a vaccine are biological matter, and so will denature if exposed to high temperatures. This can reduce or even entirely destroy a vaccine’s potency. Biological molecules also degrade naturally over time, and reducing their temperature slows the rate of degradation. However, vaccines containing aluminium-based adjuvants cannot be frozen, as sub-zero temperatures upset the adjuvants’ structures, rendering them ineffective.
This is why the World Health Organization (WHO) recommends keeping most vaccines between 2°C and 8°C – though there are some exceptions. The oral polio vaccine, for instance, is notoriously unstable, and so WHO recommends storing it between –25°C and –15°C ahead of it being distributed for administration.
Keeping vaccines cold right up until they are administered (known as ‘maintaining the cold chain’) is a big challenge in lower-income countries. Many such countries have hot climates and limited, intermittent electricity supplies, making constant refrigeration difficult. Thankfully, there are a number of solutions.
One method is to use passive coolers – large vacuum flasks filled with ice that can keep vaccines cool for up to a month. Other options include battery-powered and solar-powered fridges.
However, the ultimate solution, which is currently being explored, is to create new thermo-stable vaccines that can be stored and transported at a variety of different temperatures without any loss of potency.
See our other stories on vaccination: ‘Vaccines: what’s inside?’, ‘Vaccines: how well do they work, and are they safe?’, our ethics case study on vaccination and the history of vaccination.Lead image:
US Army Africa/Flickr CC BY NC
- National Institutes of Health: Giving a subcutaneous injection [PDF]
- Advantages of intranasal vaccination and considerations on device selection (2009)
- World Health Organization: Oral polio vaccine (OPV)
- World Health Organization: Measles
- NHS: The flu jab
- NHS: HPV vaccine
- Centers for Disease Control: HPV vaccine information for clinicians
- NHS: BCG tuberculosis (TB) vaccine
- World Health Organization: Temperature sensitivity of vaccines [PDF]
- Mentalfloss: Understanding vaccination – the cold chain
- Gizmag: Young inventor’s solar-powered fridge changes lives in Africa
- Wired: This revolutionary cooler could save millions of lives
- New Scientist: Silky scheme for vaccine storage without refrigeration
- PATH: Do vaccines always need to stay cold?