All medical interventions have the potential for side effects. Whether one pursues an intervention should be determined by the benefits of the intervention weighed against the risks of not performing the intervention. This is also true for vaccines. The benefits and risks will vary depending on the exact vaccine and what disease it is being given for.
The risk that is present with all vaccines is an allergic reaction, but it is a rare and, often, mild occurrence. Potential allergens are tested for when vaccines are developed and tested for immune system response. Both the components of the solution and the viral antigens are potential allergens. Vaccines require certain components to allow for the antigens to be in solution and to elicit an immune response, including emulsifiers, adjuvants, and preservatives. Over the years, these components have been adjusted to minimize reaction and maximize long-term immunity.
Another allergy risk is how the vaccine is developed. In particular is the influenza vaccine, which is still produced in eggs. Anyone allergic to eggs and egg proteins are at risk of an allergic reaction to that particular vaccine. The occurrence of an allergic reaction may manifest as a skin rash, trouble breathing, and fever. In rare cases, a severe reaction called anaphylaxis may occur. This requires medical treatment to blunt the immune response because an allergic reaction is simply an overdone immune response by the immune system. Researchers test vaccines under development to strike a balance between enough of an immune response for protection and not enough to cause this over-reaction.
Another common risk is found with vaccines that are given as injections. The risk is a skin reaction. Anytime an invasive method, such as piercing the skin, is used, there is going to be an inflammatory reaction at the wound site, which includes the site of an injection. Common side effects are redness, soreness, itching, and swelling.
Each vaccine has its own set of potential complications. These range from potential low-grade infection with live vaccines to gastrointestinal problems and the specific side effects of the normal immune response to that particular antigen.
For more information, the CDC has the specific side effects for each vaccine that is available.
Each vaccine is tested for potential risks and monitored over time for any unknown adverse effects. The adverse effects are received and compiled by the FDA, the agency that approves vaccines and other medicines. If a vaccine shows too many adverse effects, or very severe adverse effects, it will no longer be allowed to be used.
Why Are There Risks?
Because vaccines are used to prevent health problems, people often wonder why they can be used if there are risks. This is because of the risk to benefit ratio stated above. Vaccines are used for diseases that otherwise kill a great number of people. It is a prevention method for the greater good of a population. Usually, the risk of not using a vaccine is death or deformity. The benefit of the vaccine is life, whereas the risks are usually nominal. Only in rare instances do vaccines cause severe side effects, and there have been mistakes in the past, but in the end, vaccines save more lives than doing nothing at all against the infectious diseases that run rampant in the human population. One must weigh the risks and benefits before approaching any medical intervention, and it almost always ends with the vaccine being the better choice for the majority of individuals making that decision.