When to Call Your Healthcare Provider About an Injection Side Effect

High Fever

Fevers higher than 101 F following an injection warrant a call to your healthcare provider or visit the nearest emergency room. That’s because the fever may indicate an infection caused by needle contamination.

Extreme Pain at the Injection Site

While many people dislike the idea of a shot, the good news is it is usually over quickly and causes little pain. However, if the pain persists or worsens, you should call a healthcare provider and have it checked out.

While it is not uncommon to have localized swelling or redness for a day or two following an injection (or even longer for certain types of intramuscular shots), some symptoms warrant further investigation. These include:

• Injection site that is tender to the touch
• Fever
• Body aches
• Creeping discoloration

Swelling or Hardness Under the Skin

While swelling and minor bruising can happen after a shot, they usually get better within a day or so. However, if swelling and discoloration persist, it may signify an infection.

A lump under the skin that feels soft, mushy, and painful may indicate a developing abscess. An abscess is a walled-off collection of pus. It is often warm to the touch and accompanied by enlarged lymph nodes, small bean-shaped glands that are part of the immune system.

You should never squeeze abscesses. That's because to prevent infection from spreading throughout the body, a healthcare provider must properly drain it. If you try yourself, it could burst under the skin and spread the infection through the bloodstream, causing a potentially life-threatening blood infection known as sepsis.

Signs a lump may be an abscess include:

• The lump oozes: While a bit of drainage following an injection may be expected (caused by medication leaking out of the needle track), a doctor should look at any discolored or abnormal discharge immediately.
• The swelling grows: If the lump is small and you're not sure if it's an abscess, take a pen and draw a circle along the border. If it starts to expand beyond the edge or fails to go away in several hours, call a healthcare provider to look at it as soon as possible.

A Sudden, All-Body Reaction

Following an injection, the most severe reaction is an all-body allergic response known as anaphylaxis. This type of response can occur if the body reacts adversely to the injected medication, causing a cascade of severe and potentially life-threatening symptoms. Anaphylactic reactions following vaccination are rare.

The first signs of anaphylaxis may be similar to those for an allergy, including a runny nose and congestion (rhinitis), and an itchy skin rash. However, within 30 minutes or so, more severe symptoms can develop, including:

• Coughing, wheezing, and shortness of breath
• Chest tightness
• Hives 
• Dizziness or fainting
• Rapid or irregular heartbeat
• Weak pulse
• Facial swelling
• Swollen or itchy lips or tongue
• Difficulty swallowing 
• A blueish tinge to the lips, fingers, or toes (cyanosis)
• Pale, clammy skin
• Nausea, vomiting, or diarrhea

People who have anaphylaxis often report having a feeling of impending doom and panic. Anaphylaxis can lead to shock, coma, or even death if left untreated.