The Tdap vaccine is a combination booster designed to protect adolescents and adults against three serious bacterial infections: tetanus, diphtheria, and acellular pertussis (whooping cough). Tetanus causes painful muscle stiffness, diphtheria can lead to breathing difficulties, and pertussis causes uncontrollable, violent coughing that is particularly dangerous for infants. The vaccine is routinely recommended for everyone, especially for pregnant people in their third trimester to pass temporary protection to their newborn, and for adults in close contact with infants. Experiencing side effects indicates the immune system is actively responding to the vaccine and building protective antibodies.
Common and Expected Reactions
The most common reactions following a Tdap shot are localized to the injection site in the muscle. It is typical to experience pain, tenderness, redness, or swelling in the arm. These mild reactions are temporary, generally beginning shortly after the injection and resolving completely within one to three days.
Beyond the immediate injection area, many people also report mild, temporary systemic symptoms. These include a low-grade fever, a headache, or a general feeling of fatigue.
These expected side effects are usually not severe enough to interfere significantly with daily activities. The risk of developing these mild symptoms is far outweighed by the protection gained against diseases that can lead to severe health complications, such as pneumonia or heart failure.
Less Frequent Systemic Reactions
Some individuals experience reactions that are less frequent than localized soreness. One such reaction is pronounced swelling of the injection arm that extends beyond the immediate site, sometimes involving the entire limb. This swelling is reported in approximately 3 out of every 100 people who receive the Tdap or a similar tetanus-diphtheria booster.
Other less frequent effects involve the gastrointestinal system and general bodily discomfort. These can manifest as mild nausea, vomiting, or diarrhea, alongside generalized body aches and muscle pain.
A fever reaching 102°F or higher is also a less frequent reaction, occurring in about 1 in 250 adults after receiving the Tdap vaccine. Although these reactions can cause greater temporary discomfort, they typically resolve without any lasting consequences.
Rare Severe Reactions
Severe adverse reactions to the Tdap vaccine are extremely uncommon. The most serious possibility is a severe allergic reaction, known as anaphylaxis, which occurs in fewer than one in a million doses administered. Anaphylaxis is an emergency requiring immediate medical intervention.
Symptoms of anaphylaxis include difficulty breathing, wheezing, persistent dizziness, a rapid heartbeat, or widespread hives. Swelling of the face, tongue, or throat also requires emergency services. These reactions are caused by an individual’s rare hypersensitivity to a vaccine component.
In rare instances, neurological complications have been reported following Tdap vaccination. These include conditions like Guillain-Barré Syndrome (GBS), a disorder where the immune system attacks the nerves. Any new onset of severe weakness, numbness, or tingling after vaccination should be reported to a healthcare provider immediately.
Managing Reactions and Red Flags
Most common side effects can be managed at home using over-the-counter remedies. For pain or swelling at the injection site, applying a cool compress can help alleviate discomfort. Over-the-counter pain relievers, such as acetaminophen or ibuprofen, can also be used to manage localized pain, headache, or a mild fever.
Contact a primary care provider if a fever becomes high or if common symptoms persist for longer than 72 hours. Swelling that is very painful, or redness that continues to worsen after a few days, should also prompt a call to a doctor.
Certain symptoms are considered red flags and require immediate emergency care. Any sign of a severe allergic reaction, such as difficulty breathing, persistent dizziness, or swelling of the face or throat, requires calling emergency services. Reporting any significant adverse events to health authorities, such as the Vaccine Adverse Event Reporting System, is also recommended to help monitor vaccine safety.