Flu Shot Side Effects: Duration, Common Reactions & Ways to Feel Better
By Dr. Vishesh Bharucha +2 more
Medically reviewed by Dr. Vishesh Bharucha
Last updated: Sep 18, 2025 Published on: Sep 18, 2025
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By Dr. Vishesh Bharucha +2 more
Table of Contents
Flu or influenza is an infection caused by influenza viruses, typically the A, and B types. Influenza spreads easily and can affect people of any age, from children to the elderly1,2. While most of them recover within a few days, uncomplicated flu takes about 5–7 days to resolve, and tiredness or cough can last up to 2 weeks3.
Sometimes flu can lead to serious problems like pneumonia (directly caused by the flu, or by superimposed bacterial infection) and worsening of diseases like asthma, diabetes, and heart problems. Every year, millions of people get affected by flu worldwide, with many even needing hospital admission. Taking a flu shot is the most effective way to lower this risk. It not only helps prevent flu infection but also reduces the risk of complications and hospitalisation4,5.
While the benefits of the flu shot are clear, some people worry about what happens after the flu shot and whether they will get side effects. Like any vaccine, the flu shot may cause some side effects, but they are mostly mild and short-term6. In this blog, let’s see what the flu shot side effects are, how long they last, and simple ways to feel better.
There are three main types of influenza vaccines: the inactivated influenza vaccine, the live attenuated influenza vaccine and the recombinant influenza vaccine (RIV). The inactivated vaccine contains killed viruses and is given as an injection. The live attenuated vaccine is made from weakened viruses and is available as a nasal spray1,7. Recombinant vaccines, such as FluBlok, are newer vaccines made without using the flu virus or eggs, especially for people with egg allergies. These are available in some countries but are not common in India.
In India, the commonly used form is the inactivated influenza vaccine, which is administered as an injection into the arm muscle in adults, and into the thigh muscle in infants1,7. It is recommended for people at higher risk, such as children aged six months and older, adults over 65 years, pregnant women, healthcare workers, and people with chronic illnesses like asthma, diabetes, or heart disease1. It is not recommended for all adults, unlike in some countries such as the US, where vaccination is advised for everyone4.
When you get the flu shot, your body’s immune system is activated to produce protective antibodies against the flu virus. The antibodies are developed within 2 weeks after you get your flu shot. These antibodies are mainly responsible for the effectiveness of vaccines and protect children and adults from severe infection. When you get infected with flu, your body also produces antibodies, but this protection works only against the same type of flu and slowly fades away, especially because the flu virus keeps changing its form. In the same way, the antibodies produced by the vaccine gradually decline over time4,9. Therefore, it is recommended to get your flu shot yearly once before the flu season to protect yourself.
You can prepare yourself by following these simple things before you get a flu shot:
After getting the flu shot, it’s normal to experience mild soreness, pain, swelling or redness at the site of injection. Small children may become irritable and cry excessively. These signs are generally nothing to worry about and resolve soon on their own4,6.
Some individuals, especially adolescents, may have a fainting sensation during or after the vaccination, but this is mainly due to anxiety related to the injection process and not the side effects of injection per se. If you feel dizzy, you will be made to sit for 15-20 mins and monitored after the injection11.
There are some other minor or rarely major side effects that may occur after getting the flu shot. We’ll discuss these in detail in the following sections.
Flu shots are generally safe, but mild flu vaccine side effects may be seen.
Serious flu shot side effects are very rare. Only 1 to 2 people out of 1 million doses may have a severe allergic reaction seen as:
These reactions can sometimes start even after leaving the clinic or hospital15,16.
In very rare cases, some people may have a risk of developing flu vaccine long-term side effects like Guillain-Barré syndrome (GBS) a few days or weeks after vaccination. GBS is a rare disorder where the immune system attacks the nerves, causing weakness and, in some cases, paralysis. However, the chance of getting GBS from the flu vaccine is extremely rare, about 1 to 2 people in every 1 million. This risk is much lower than getting GBS from catching the flu itself17.
Flu vaccines are made with viruses that are no longer active or with particles that mimic the flu virus, so they cannot cause flu directly. Instead, they help your body build an immune response and produce antibodies against flu6,9.
Sometimes, a person may still get flu after being vaccinated, but this is not because of the vaccine. It could happen if you are exposed to flu within 1–2 weeks after the shot, before your body develops full protection, or if you catch a flu strain not covered by the vaccine.
The nasal spray flu vaccine (not available in India) contains a weakened form of the virus. In rare cases, it may cause mild cold-like symptoms, but not true flu. This is not seen in other types of flu vaccines4,7.
In fact, it helps protect you and usually makes illness milder if you do get infected. Vaccinated people have a much lower risk of hospitalisation and death from flu.
Other reasons someone might get flu after vaccination include catching it before the body has finished building protection, facing a flu strain not covered by the vaccine, or the vaccine’s effect wearing off later in the season4,9.
Most flu shot side effects are mild, like pain at the injection site, headache, tiredness, and muscle pain, usually go away within 1 to 3 days. In some cases, soreness or swelling at the injection site may last up to 7 days14.
Some may develop mild allergic skin reactions, like hives, which settle within 24 hours. Rarely, delayed reactions like skin rashes are seen which may occur hours to several days after receiving the flu shot18.
Serious allergic reactions, such as angioedema (swelling of the face, lips, or throat) or anaphylaxis, occur within minutes to a few hours, but are very rare. With proper treatment, symptoms usually resolve within hours if not severe19,20.
Guillain-Barré Syndrome (GBS) is an extremely rare flu vaccine long-term side effect that may occur 2 to 6 weeks after vaccination. Recovery may take months to years, depending on severity21,22.
The flu vaccine side effects can be managed by doing these simple things at home:
The flu vaccine may cause mild side effects, but these are very minor compared with the benefits. It protects against influenza virus infection and greatly lowers the risk of serious illness. While no vaccine gives 100% protection, people who get the flu after vaccination are far less likely to experience severe complications, hospitalizations and even prevents ICU admissions. This protection is especially important for high-risk groups such as children, pregnant women, older adults, and people with chronic conditions. Even if you get the flu after vaccination, it is usually milder when compared with those who are not vaccinated. This makes it important to get your yearly flu shot26,27.
You should see a doctor after a flu shot if pain or fever is not relieved by paracetamol, or if symptoms are severe, worsening, persistent, or causing concern. Seek medical advice if these symptoms last more than seven days. Seek urgent care immediately if you experience flu vaccine side effects like severe allergic reactions, including difficulty breathing, swelling of the face or throat, a rapid heartbeat, widespread rash, dizziness, or weakness16,25.
Flu shots are safe and effective, with side effects that are usually mild and short-term. They protect against flu infection, reduce the risk of complications, hospitalizations, and ICU admissions, and also protect high-risk groups such as children, pregnant women, older adults, and those with other long-term health conditions. Getting a flu vaccine every year can protect you and those around you, helping keep the community healthy throughout the flu season.
Yes, you can get a flu shot during pregnancy. It helps protect you from getting the flu, reduces the risk of hospitalization, and passes antibodies to your baby before birth28.
Yes, people over 60 can get stronger flu vaccines, such as the high-dose or adjuvanted flu vaccine, which boost the immune system and provide better protection than the regular flu shot. These vaccines also help reduce complications.
Yes, you need to get a flu shot every year because the influenza virus changes constantly. Annual vaccination prepares your body to fight the current type or strain of flu circulating that season.
For most adults, only one injection is needed. However, children aged 6 months to 9 years who are receiving the flu shot for the first time, and people who have undergone transplant or have special health conditions, may need two shots, spaced one month apart8.
Disclaimer: The information provided here is for educational/awareness purposes only and is not intended to be a substitute for medical treatment by a healthcare professional and should not be relied upon to diagnose or treat any medical condition. The reader should consult a registered medical practitioner to determine the appropriateness of the information and before consuming any medication. PharmEasy does not provide any guarantee or warranty (express or implied) regarding the accuracy, adequacy, completeness, legality, reliability or usefulness of the information; and disclaims any liability arising thereof.
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