Vaccine Safety

Vaccine Safety

Are vaccines safe?

Vaccinations are not offered to members of the public until independent experts have signed off that they are safe and offer the highest level of protection. Licenses are then required, from the European Medicines Agency for example, before companies are able to market and distribute the vaccines.

There are many stages to vaccine development including a pre-clinical stage, clinical development, regulatory review and quality control following manufacture. Clinical development is generally broken into three phased processes:

  • Phase I – small groups of people receive the trial vaccine
  • Phase II – the clinical study is expanded and the vaccine is administered to specific groups of people displaying certain characteristics (e.g. different ages, underlying conditions, ethnic backgrounds etc.) and physical health); similar to those for whom the new vaccine is intended.
  • Phase III – the vaccine is given to thousands of people and tested for both efficacy and safety.

As with any medicine, vaccines are highly regulated products. There are checks at every stage in the development and manufacturing process. Moreover, once authorised, vaccines undergo continued monitoring throughout their use in the wider population to make sure they are safe for those who receive them.

What goes into a vaccine?

As vaccines are generally complex biological products that contain a number of substances in tiny doses that ensure the quality of the final product. Each substance (also referred to as excipient) is included in order to perform a specific function to ensure the final vaccine is safe and effective.

Vaccines will include active ingredients, which are parts of the virus or bacteria to challenge the immune system into making the required response. The other main ingredient is water. Other inactive ingredients, weighing a few milligrams or less, will be included to help improve the immune response or to preserve or stabilize the vaccine contents. Read more HERE.

Just how effective are vaccines?

Vaccine efficacy and effectiveness are measures that compare the rates of disease between vaccinated and unvaccinated people. Efficacy is measured in controlled clinical trials, whereas effectiveness is measured once the vaccine is approved for use in the general population. Vaccines will only be recommended if they are deemed safe and effective; the majority of childhood vaccines for example are found to be between 90 – 99% effective. Read more on the Vaccine Knowledge project HERE.

No vaccine will offer 100% protection. Some individuals will fail to mount an initial immunological response to the vaccine, and so infection may occur after vaccination; for example, around the 5–10% of children will not respond to the measles component of the first dose of MMR, which is why risk of infection is reduced by offering an additional vaccine dose later in their vaccine schedule. It is also possible for an individual to have an initial immune response but this then wanes over time; the Covid-19 vaccine is an example of this, where booster doses are recommended after several months.

How is vaccine safety monitored?

Authorised vaccines are monitored on a global scale via various health reporting systems. Since some side effects may not have been identified prior to licensing, especially if they occurred very rarely, careful surveillance is required throughout vaccine use. If there is any suspicion that an adverse reaction has occurred following vaccination it should be reported.

In Gibraltar, as per the UK, vaccine and medicine safety is collected and monitored via the Yellow Card Scheme [read more here]. Other sources of information are also used to feed into the global reporting systems, for example epidemiological databases, medical studies and literature, and other worldwide organisations.

Global research shows that immunisation is the safest way to be exposed to potentially life threatening illnesses and gain the best level of protection. You are far more likely to be seriously injured or permanently disabled by a vaccine-preventable disease than by a negative side-effect of a vaccine.  For example, a rare side effect of wild measles infection is Subacute sclerosing panencephalitis (SSPE); Click here to view video.

What side effects are common following vaccination?

Common reactions or adverse events that follow immunisation include:

  • pain or redness at the injection site.
  • localised reactions that occur within a few hours of the injection, for example swelling, itching or a rash. These reactions are usually mild and short lived.
  • systemic reactions that may occur with a few hours or after a few days (timings of reactions often vary according to the individual’s age and the vaccine they received). Examples of systemic reactions include fever, nausea, loss of appetite, muscle aches, headache, and irritability.

Your healthcare provider will provide advice on how to manage potential side-effects you may have during your vaccination appointment. Local reactions are usually self-limiting and do not require any treatment. If they appear to cause discomfort, then paracetamol or ibuprofen can be given (according to manufacturer instructions).

Severe reactions to vaccinations are very rare and should be weighed against the potentially life limiting side-effects of contracting the actual virus or disease.

Should I be concerned about anaphylaxis?

Anaphylaxis is a severe and potentially life-threatening allergic reaction that typically occurs within minutes to exposure to an allergen. Anaphylactic reactions to vaccines are extremely rare but have the potential to be fatal.

Most anaphylactic reactions are seen in individuals who have no previously known risk factors; several checks are made prior to vaccination to prevent any potential reactions.

The members of the healthcare team onsite during and following vaccination are trained to both recognise and treat cases of anaphylaxis promptly.


Where can I read more?

The ‘Green Book’ is a publication that is updated to provide the best evidence based information surrounding immunization to health care professionals. Read about vaccination procedures, vaccine effectiveness, side effects and the diseases vaccines protect against in the book HERE.

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