The active substances activate your body’s immune system to build up immunity against the pathogen that is targeted by the vaccine. The page ‘How does vaccination work?’ explains how.

The active substances in vaccines can be divided into three groups.

Active substance 1: fragments of pathogens

Fragments of pathogens are usually produced by culturing the pathogen and then snipping it into pieces. The tiny parts that trigger a good immune response are isolated and put into the vaccine. 

Cultivating bacteria requires a good medium. When the bacteria are added, they start to multiply. Viruses do not start replicating on their own. They need live cells for this. The live cells are infected with the virus, and after a few days or weeks the virus has replicated many copies. The bacteria or viruses can then be snipped into pieces.

The fragments used for the HPV vaccine and the hepatitis B vaccine are produced using a different method. HPV and hepatitis B are both viruses, but whole viruses are not used to make these vaccines. Instead, yeast cells are taught to make a specific part of the virus. This is done by embedding a small piece of genetic material from the viruses into the yeast cells. This genetic material tells the yeast cells what those fragments of the virus look like. The yeast cells are then cultured, and in the process they also produce these virus fragments. The virus fragments are then extracted from the yeast cells. This is known as the recombinant DNA method.

Vaccines that contain fragments of pathogens are called ‘inactivated vaccines’.

Active substance 2: toxin from bacteria

Tetanus and diphtheria are caused by the toxin produced by the bacteria. To produce the vaccines that protect against these diseases, the bacteria are cultivated until they produce a poisonous substance (toxin). The toxin is treated with chemicals to make it harmless. After this chemical treatment, it is called an anatoxin. It does not make you ill, but it can teach your immune system to recognise it. 

These vaccines are also called ‘inactivated vaccines’.

Active substance 3: live attenuated (weakened) viruses

Viruses can only replicate inside living cells. That is why live attenuated (weakened) viruses are made by culturing cells that have been infected with the virus. During cell culture, a special process is used to weaken the virus, while still keeping it alive. Since the virus has been weakened, it can no longer make you seriously ill. After vaccination, it can only cause a mild infection. And because of that mild infection, these vaccines trigger very good immune responses in the human body. It also provides long-term protection. 

These vaccines are called live attenuated vaccines.

Excipients are added to make sure that the vaccines work as intended. The excipients used in vaccines have been researched to make sure they are safe, and have been used many times.

Excipients in vaccines can be divided into three groups:

Excipient 1: fillers

A filler makes it easier to administer the vaccine. The vaccine only contains a very tiny amount of the active substance – so tiny that it cannot be administered via an injection. To increase the volume of the vaccine and make injection possible, fillers are added.

Fillers are liquids consisting of water mixed with salts, sugars and stabilisers. These salts and sugars are added so that the liquid closely resembles the fluids already present in the human body. This is necessary to make sure the vaccine is safe. Using sugar can also help reduce discomfort during the injection. Sugars also give the vaccine a longer shelf life. Gelatine or amino acids may also be added to vaccines to improve their storability.

Vaccines that are given via oral drops also contain a small amount of added sugar. One example is the rotavirus vaccine. This makes it taste better for babies and children, so they swallow all the drops.

Excipient 2: immune system stimulants

Sometimes it is difficult for the immune system to recognise the pathogen fragments (active substance 1, see above). To make it easier, the fragments are attached to a different substance. This connection helps the active substances end up with the right immune cells, and ensures that the immune cells respond strongly to the pathogen fragments.

Substances that stimulate the immune system are not harmful, but they could make side effects after vaccination a bit more intense. That includes redness, swelling or pain at the injection site. Read more on the page about research on substances used in vaccines.

Excipient 3: preservatives

Preservatives extend the shelf life of a vaccine. They prevent the growth of bacteria, yeast or fungi in the vaccine.

Preservatives are harmless to humans. Vaccines contain very small amounts. Read more on the page about research on what is in vaccines.

Substances are used to culture the pathogens and then process them for use in a vaccine. These substances are removed before the result is added to the vaccine, but sometimes very small amounts remain. These are called residues. Any remaining residues are present in such small amounts that they have no effect on human health.

Antibiotics

Antibiotics (also known as antimicrobial agents) are used to kill bacteria. They are added when the pathogens are being cultivated to prevent the growth of any unintended bacteria. The antibiotics are removed before the vaccine is put in vials or syringes. Very small traces of antibiotics can sometimes still be left in the vaccines.

These tiny amounts of residual antibiotics rarely cause any side effects. Moreover, the risk of an allergic reaction due to antibiotics in vaccines is minimal. This is because the antibiotics that are usually given to sick children are different from the antibiotics that are used in the production of vaccines.      As a result, children who receive antibiotics do not have to worry that the vaccination has made them allergic to that medicine. If they are ill, they can still take antibiotics.  Is your child allergic to antibiotics? Then tell the nurse or doctor before the vaccination is given. Read more about allergic reactions on the page about side effects.

The table below lists the antibiotics used to produce vaccines in the context of the National Immunisation Programme.

Cells

Viruses can only replicate inside living cells. That is why the viruses used in live attenuated vaccines are cultured in living cells. The cells are made in a laboratory through cell division. This generates many identical cells and does not require any live or dead animals or humans. 

Once the virus is made, it has to be removed from the cells. Traces of the cells may be left behind. These traces are filtered out of the vaccine as much as possible, but a minimal quantity of cell DNA may still be present. After vaccination, the body breaks down this DNA. That is why it is not dangerous.

Read more about how cells are used to make vaccines on the page about research into the contents of vaccines.

No chicken egg protein in vaccines included in the National Immunisation Programme 

Vaccines in the National Immunisation Programme are produced without using any chicken eggs. Therefore, none of the vaccines in the National Immunisation Programme contain any residues of chicken egg protein. Children who are allergic to chicken egg protein can be vaccinated with these vaccines without any problems.