Vaccination is one of the most effective public health tools, preventing the spread of infectious diseases and protecting millions of lives [4, 7]. Vaccines stimulate the immune system, forming a reliable and long-term response to disease pathogens [1]. Like any medical intervention, vaccination can be accompanied by side effects, including allergic reactions. Although severe allergic reactions to vaccines are extremely rare, it is important to know how to recognize them and what steps to take.
Vaccination and the immune system: how does it work?
Vaccines stimulate the immune system, forming protection against infections [1, 5]. Most side effects after vaccination are mild and transient, such as pain at the injection site or a slight fever [7]. However, in rare cases, more pronounced reactions can occur, including hypersensitivity [1, 7].
What is an allergic reaction to a vaccine?
Allergic reactions to vaccines are undesirable immune system responses to their components. They are classified by the time of onset [3]:
- Immediate reactions: Within 4 hours after administration, potentially IgE-mediated, requiring allergological evaluation [3].
- Non-immediate reactions: Manifesting after 4 hours [3].
Local reactions (pain, swelling, redness) are the most common and usually do not require evaluation [3]. Systemic reactions, especially anaphylaxis, are serious and require immediate assistance [3, 4].
Symptoms of vaccine allergy: how to recognize them?
Symptoms of an allergic reaction can range from mild to life-threatening. Their timely recognition is critically important.
Mild and moderate symptoms:
- Redness, itching, or swelling at the injection site that exceeds typical reactions [3].
- Urticaria (hives), maculopapular rash, mild swelling of the face/lips/eyes (angioedema) [8].
- Mild difficulty breathing or wheezing [8].
Severe symptoms (anaphylaxis):
Anaphylaxis is an acute, potentially fatal systemic reaction. It is extremely rare (<1/100,000 vaccinations) but can develop in any patient [4]. For COVID-19 vaccines mRNA-1273 and BNT162b2, the incidence of anaphylactic reactions was estimated at 2.5 and 11.1 cases per million doses, respectively [2].
Signs of anaphylaxis include:
- Sudden difficulty breathing, shortness of breath, wheezing, feeling of tightness in the chest.
- Generalized urticaria, severe itching, angioedema.
- Sudden drop in blood pressure, dizziness, fainting.
- Rapid heartbeat, nausea, vomiting, abdominal cramps.
These symptoms require immediate emergency medical attention [3].
Risk factors and vaccine components that cause allergies
Although allergic reactions are unpredictable [4], those at increased risk include:
- Individuals with an allergy to a previous vaccine or its components [4].
- Patients with a history of drug allergies [2].
Vaccine components capable of causing allergies include [6]:
- Gelatin: a stabilizer in some vaccines.
- Egg protein: in vaccines grown in chicken embryos (e.g., influenza, measles, mumps, rubella).
- Other components: excipients (antibiotics, preservatives) [2].
General allergies (to pollen, food) are usually not a contraindication [4]. However, if you have an allergy to vaccine components or a history of serious reactions, discuss the risks with your doctor [2, 4].
First aid and further management of an allergic reaction
If you suspect an allergic reaction after vaccination, act quickly:
- Notify medical staff immediately: If the reaction occurs in the clinic, contact a doctor.
- Call emergency services: In case of severe symptoms (difficulty breathing, swelling, drop in blood pressure), call an ambulance immediately.
- Antihistamines: May be prescribed for mild symptoms (hives, itching) [8].
- Epinephrine (adrenaline): Immediate administration is life-saving in cases of anaphylaxis [8].
After the acute reaction is managed, an evaluation by an allergist may be required to identify the specific allergen [3]. This will help determine safe vaccination options in the future, possibly under observation or using alternative vaccines [4].
Vaccination and allergy: the importance of an informed decision
Unfounded fears can lead to incomplete vaccination, putting individuals at risk of serious infectious diseases [4]. Allergic reactions, including anaphylaxis, are rare but require attention [3, 4]. Current guidelines emphasize that patients with allergies deserve access to recommended vaccines unless the risks outweigh the benefits [4]. Always discuss your allergy history with your doctor before vaccination to make an informed and safe decision.
Sources
- [1] Adverse reactions to vaccination: from anaphylaxis to autoimmunity. (The Veterinary clinics of North America. Small animal practice, 2018) https://pubmed.ncbi.nlm.nih.gov/29195924/
- [2] Allergy to COVID-19 vaccines: a current update. (Allergology international : official journal of the Japanese Society of Allergology, 2021) https://pubmed.ncbi.nlm.nih.gov/33962863/
- [3] Diagnosis and management of hypersensitivity reactions to vaccines. (Expert review of clinical immunology, 2020) https://pubmed.ncbi.nlm.nih.gov/32838592/
- [4] Vaccination and allergy: EAACI position paper, practical aspects. (Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology, 2017) https://pubmed.ncbi.nlm.nih.gov/28779496/
- [5] Duality of human responses after COVID-19 vaccination. (Biomolecules, 2024) https://pubmed.ncbi.nlm.nih.gov/39456253/
- [6] Vaccination and allergy. (Current opinion in otolaryngology & head and neck surgery, 2004) https://pubmed.ncbi.nlm.nih.gov/15167034/
- [7] Vaccines and autoimmunity. (Nature reviews. Rheumatology, 2009) https://pubmed.ncbi.nlm.nih.gov/19865091/
- [8] Acute hypersensitivity reaction with maculopapular exanthema and angioedema after low-dose amitriptyline for migraine prophylaxis: A case report. (Cureus, 2025) https://pubmed.ncbi.nlm.nih.gov/41049968/
Disclaimer: The information provided in this article is for reference purposes only and cannot replace an in-person consultation with a qualified medical professional. Always consult a doctor for diagnosis and treatment.