Getting an updated flu shot every year – ideally as early on in the season as possible – is the best way to protect against getting the flu. The vaccines are designed to protect against a few (usually three) different strains of the influenza virus that are anticipated to be the most harmful that year, so getting one greatly decreases your chances of getting sick. They’re not foolproof however: they aren’t 100% effective, and some people do experience side effects.
Some people mistake mild side effects following a vaccine for having actually contracted the flu, albeit a mild one, but that isn’t true: for an injection, there are two forms, one of which contains a sample of the flu virus that has been inactivated so that it can’t infect you, and one that contains no part of the virus at all. The nasal spray version of the vaccine does contain live virus cultures, but they’re been weakened so that they can’t spread or infect the lungs.
If you get an actual flu shot – meaning you receive the vaccine through an injection – you may notice redness or swelling at the injection site, and there may be some lingering soreness, but this is common in many injections. In rarer cases, some people experience achiness in the body or develop a low-grade fever (under 101 degrees); some also experience headaches. These side effects usually begin shortly after receiving the shot and they clear up within two days or less. Over the counter pain medication such as ibuprofen is enough to manage them.
The nasal spray vaccine tends to come with more side effects than the injection. While they share the potential for developing body aches, headache, and a mild fever, the nasal spray is more likely to cause nausea as well. A runny nose is fairly common, which may or may not lead to a sore throat from post-nasal drip, and wheezing in the chest.
In rare cases, there are more severe reactions that occur within a few hours of getting vaccinated. These include difficulty breathing, swelling around the eyes or lips, hives on the skin, and a high fever (more than 101 degrees). Weakness, dizziness, paleness, and a racing heart are also potential serious symptoms. If you experience any of these, get medical attention immediately and verify that your healthcare provider will report it to the Vaccine Adverse Event Reporting System (VAERS).