What are the causes of a severe adverse reaction to a vaccine (Vaccination)?

From the Guidelines

If you experience a severe vaccine reaction, seek immediate medical attention by calling emergency services or going to the nearest emergency room. Severe reactions like anaphylaxis typically occur within minutes to hours after vaccination and may include difficulty breathing, swelling of the face and throat, rapid heartbeat, dizziness, or a severe rash. While waiting for help, lie down with legs elevated if feeling faint. If you have an epinephrine auto-injector (EpiPen) and know how to use it, administer it according to instructions if symptoms suggest anaphylaxis. After emergency treatment, report the reaction to your healthcare provider and to the Vaccine Adverse Event Reporting System. Severe vaccine reactions are rare but require prompt medical intervention because they can be life-threatening. Most vaccine side effects are mild and resolve on their own, but severe reactions need immediate professional medical care to prevent complications.

Key Considerations

• Severe vaccine reactions can be life-threatening and require immediate medical attention 1.
• Anaphylaxis is a severe allergic reaction that can occur within minutes to hours after vaccination and may include symptoms such as difficulty breathing, swelling of the face and throat, rapid heartbeat, dizziness, or a severe rash.
• If you experience any of these symptoms, seek immediate medical attention and administer epinephrine if available and you know how to use it.
• After emergency treatment, report the reaction to your healthcare provider and to the Vaccine Adverse Event Reporting System.

Prevention and Management

• Contraindications and precautions to vaccination dictate circumstances when vaccines will not be administered or should be deferred 1.
• A contraindication is a condition in a recipient that increases the risk for a serious adverse reaction, and a vaccine will not be administered when a contraindication is present.
• If a precaution is present, vaccination should generally be deferred but might be indicated if the benefit of protection from the vaccine outweighs the risk for an adverse reaction.

Reporting and Follow-up

• After a severe vaccine reaction, report the reaction to your healthcare provider and to the Vaccine Adverse Event Reporting System.
• Follow-up with your healthcare provider to discuss any further treatment or precautions needed.

From the Research

Severe Vaccine Reaction

• Severe vaccine reactions can occur in some individuals, and these reactions can be caused by various factors, including immune responses to the active vaccine components or vaccine excipients 2.
• Most vaccine-associated adverse events are self-limiting and resolve within days, but some can be severe and require medical attention 2.
• A study proposed a hypothesis that the majority of vaccine-associated reactogenicity adverse events are caused by temporal histamine intolerance in vaccinees, which can be evaluated by detecting elevated histamine levels in vaccinees corresponding to the timing of symptoms onset 2.

Management of Severe Vaccine Reactions

• Epinephrine is the first-line treatment for anaphylaxis, a severe and life-threatening allergic reaction that can occur after vaccination 3, 4.
• Antihistamines may also be used in the management of anaphylaxis, but their role is still being studied, and some guidelines recommend against their use as initial treatment 3, 4.
• Corticosteroids are not recommended for the initial treatment of anaphylaxis, and their use should be revisited 3.

Specific Vaccine Reactions

• A study found that anaphylaxis occurred in 40.6 cases per million after mRNA COVID-19 vaccination, and most cases were in women with a history of allergic disease and asthma 5.
• The same study found that systemic allergic symptoms, not fulfilling anaphylaxis criteria, were more common in Pfizer-BioNTech-vaccinated patients than in Moderna-vaccinated patients 5.
• Another study found that most people with a reaction to the initial mRNA vaccine can be safely revaccinated, and patients with anaphylaxis to COVID-19 vaccines benefit from physician-observed vaccination 5.

Historical Context

• A study from 1978 found that the administration of triple typhoid vaccine to dogs resulted in renal hyperemia, which was associated with elevated renal secretory rates of renin and prostaglandin E and F, and was reversed by meclofenamate, an inhibitor of prostaglandin synthetase 6.