All medicines have side effects. But vaccines are among the safest, and the benefits of vaccinations far outweigh the risk of side effects.
When you're considering a vaccination for yourself or your child, it's natural to focus on the potential side effects.
But a better approach is to try to balance the benefits of having a vaccine against the chances of harm.
It's quite common to have redness or swelling around the injection site, but this soon goes away.
Younger children or babies may be a bit irritable or unwell, or have a slight temperature. Again, this usually goes away within 1 or 2 days.
Read this NHS leaflet about the common side effects of vaccinations in babies and children up to 5 years of age (PDF, 118kb).
In much rarer cases, some people have an allergic reaction soon after a vaccination.
This is usually a rash or itching that affects part or all of the body. The GPs and nurses who give the vaccine are trained in how to treat this.
On very rare occasions, a severe allergic reaction may happen within a few minutes of the vaccination.
This is called an anaphylactic reaction. It can lead to breathing difficulties and, in some cases, collapse.
Remember that anaphylactic reactions are extremely rare (less than 1 in a million).
Vaccination staff are trained to deal with this, and these reactions are completely reversible if treated promptly.
Vaccination is different from giving medicine to an unwell child to make them better. The benefits of vaccination are invisible.
The idea is that your child will not become ill with measles or end up in intensive care with meningitis.
It may be tempting to say "no" to vaccination and "leave it to nature".
But deciding not to vaccinate your child puts them at risk of catching a range of potentially serious, even fatal, diseases.
In reality, having a vaccination is much safer than not having one.
They're not 100% effective in every child, but they're the best defence against the epidemics that used to kill or permanently disable millions of children and adults.