What are the most common risks after shots?

Parents want to keep their kids as healthy as possible, but with the overwhelming amount of information found in media these days, it is hard to know what is safe and what risks really are when it comes to vaccines.

Nothing we do is without risk. The most risky thing most of us do daily is to get in a car and drive somewhere. We can minimize the risk by wearing a seat belt and putting our kids in the proper sized car seat, obeying the traffic laws, and adjusting our driving to the road and weather conditions, but there is always the chance of an accident. For most of us, the risk of an accident is outweighed by the benefits of getting to where you need to go. 

Vaccines are no different. The benefits are many, including preventing early death from infection. The risks are often overblown, but do exist.

You might have read somewhere that you should read the package insert of vaccines before allowing your child to get a vaccine. This advice is somewhat misguided. The package insert has a lot of information, but it is designed for legal reasons, not consumer information sharing. Anti-vax groups encourage the reading of them to learn risks of the vaccines, but this can lead to undue fear and confusion. Not all problems recorded in the adverse reactions section of the package insert are due to the vaccine. If someone fell out of a tree and broke his leg after a vaccine and reported it during vaccine trials, "broken leg" will be listed as a reaction. It does not mean that the vaccine broke the leg or caused the broken leg in any way, but it is reported in a way that can make it look like there is a cause and effect relationship. For a more detailed description of package inserts, see Package Inserts - Understanding What They Do (and Don't) Say. 

The risks of all vaccines are similar. Specific risks can be found on the Vaccine Information Sheets (which are designed to educate consumers about risks and benefits), but in general the risks of any vaccine may include:

• Pain with injection. This is very subjective. Most babies cry, but typically as soon as they are cuddled by a parent they quickly calm down. Toddlers are more prone to longer crying times, but that often starts unrelated to the vaccine and is not solely due to pain. It is often due to their frustration and/or fear of being in the doctor's office. Older kids often will say the pain was less than they feared, but some do complain for several minutes. Moving the arms or legs that were injected can help ease this pain. 
• Fever. A mild fever can occur for a day or two after many vaccines. Most kids do not need any fever reducers for this. The fever reducers might even reduce some of the effectiveness of the vaccine, so are not routinely recommended after vaccines. If the temperature is over 102F or the child is very fussy with the fever, it is okay to use a fever reducer. These higher fevers are not common after vaccines, but are possible.
• Fussiness or feeling mildly ill. Infants can be fussy for a few days and older kids might say they feel tired or have a headache. Some kids (and adults) will feel like they're getting sick, but it never evolves into an illness and it stays mild. Extra sleep would be beneficial, but typically no treatment is needed. 
• Non-stop crying. While unusual, it is possible that an infant will cry for hours after one or more vaccines. If this occurs, you can try a pain reliever. If the crying doesn't stop, it might be wise to have your child examined since it might be that something significant is going on causing the crying. 
• Seizure. It is not common to have a seizure after a vaccine, but whenever a child under 5-6 years of age has a fever, it is possible to have a fever seizure. Most fever seizures are from viral illnesses, some of which are prevented by vaccines. Vaccines rarely cause fever seizures, but if the temperature increases rapidly after a vaccine in a susceptible child, it is possible. If a child has a fever seizure, it is scary to watch but does not lead to permanent brain damage.  
• Pain, tenderness and swelling of the injection site for several days after the injection. Some vaccines, such as DTaP and Tdap, are more prone to swelling and redness than others. The most swelling tends to happen after several doses of these vaccines, such as with kindergarteners, tweens, or adults. My son's arm was so swollen after kindergarten shots that he couldn't fit into some of his shirts with narrow arms, but it was a normal shot reaction. With a shot reaction the inflammation begins a few hours after vaccination, peaks 24 h to 48 h afterward and resolves within one week. Tenderness is usually at its worst during the first few hours and resolves as the reaction enlarges. The amount of swelling and redness is more significant than pain or tenderness with a classical vaccine reaction. 
• Infection of the injection site. Very rarely the area can become infected (cellulitis) but this is exceedingly rare now that most childhood vaccines come in single dose syringes. Cellulitis can evolve rapidly -- often within 12 h to 24 h. Diagnosis is based on the symptoms of redness, pain, swelling and warmth, usually with fever and ill appearance. Most redness and swelling is a normal shot reaction and not a sign of infection, but if your child seems ill along with a painful red and swollen area where the vaccine was injected, it might be wise to have your doctor take a look at it. 

It's hard to see, but this is my arm 2 days after a Tdap. The area was swollen, warm and red. The redness has irregular borders, looking lacy in appearance, which is common in shot reactions. I didn't take any pain relievers. I tried moving my arm around a lot and that helped.