Tanya Altmann, MD, FAAP: Vaccines nowadays are very safe, and so we rarely see serious side-effects or reactions. Rarely, a baby maybe a little fussy after getting vaccines, or have a little fever. And if that's the case, your pediatrician may recommend a fever reducer such as Acetaminophen. If your child has a very rare reaction, such as an allergic reaction, like hives trouble breathing, a really high fever, or they're just not acting well, then call your pediatrician right away. Rarely, a child will have a local reaction at the site of the injection. So if you notice any redness, or tenderness, or swelling, you can put a cool compress on it. Give your child a pain relieving medications such as Acetaminophen, and it should go away in about 24 to 48 hours. Another thing that we rarely see in the infants is a pea sized lump under the injection site, and this is normal, does not cause any pain or discomfort, and will also go away on its own with time. If you notice anything more serious, which again would be rare, such as spreading redness or pain that's really increasing in intensity, call your pediatrician.