Yellow fever injections have similar side effects to other vaccines. Most people with side effects only experience mild discomfort: the site of the shot may become sore, bruised, and swollen; there may also be a mild fever accompanied by achiness and chills. The few people who do have severe symptoms may experience difficulty breathing, behavioral changes, seizures, high fever, irregular heartbeat, hives, and other symptoms that need immediate medical treatment. Side effects of yellow fever injections usually occur within the first hour after a shot is given, but they can also develop within 30 days after the injection.
Medical practitioners watch more carefully for side effects in people who have never had yellow fever injections. Without a history of vaccination, it's impossible to know how a person will react. Those who have had the injection and did not experience any side effects are extremely unlikely to develop side effects with recurring shots.
Many people only experience mild effects following a yellow fever shot, such as a soreness or stiffness at the site of the injection. A person who is mildly sore may also experience redness, bruising, and perhaps swelling at the injection site. A mild and short-lived fever may also occur. For such symptoms, medical treatment is often not necessary; symptoms should clear up with time. If one wishes, they may take over-the-counter medications to help alleviate fever and soreness.
Those who experience severe symptoms should seek medical treatment immediately. Severe side effects from yellow fever injections are generally due to allergic reactions and can be deadly. Typically, those who suffer such reactions are allergic to chickens, eggs, or gelatin—all common ingredients in vaccinations.
Those who have such allergies are encouraged to avoid travel to parts of Africa and South America, where the yellow fever virus is common. If a person with egg or chicken allergies must travel to such regions, a doctor may still recommend a yellow fever vaccine if contracting the virus is believed to be more life-threatening than an allergic reaction from the shot. Doctors can provide the vaccination in smaller doses in hopes of inducing a less severe allergic reaction.
Certain demographics are more likely to suffer severe side effects to yellow fever injections than others. As mentioned, those with poultry allergies are at risk. Pregnant women are also advised not to get the vaccine, as it may harm unborn children. Those with weak immune systems and who have experienced organ failure as a result of a serious illness may also be advised against the injection. Children under nine months of age, and especially those younger than six months, are considered especially vulnerable to negative side effects.