What are adverse reactions following vaccination in children and what is the definition of Adverse Events Following Immunization (AEFI)?

Adverse Reactions Following Vaccination in Children and Definition of AEFI

Definition of AEFI

Adverse Events Following Immunization (AEFI) are any untoward medical occurrences that follow immunization and do not necessarily have a causal relationship with the vaccine administration. 1 These encompass both true adverse reactions (causally related to the vaccine) and coincidental events that occur in temporal proximity to vaccination but are not caused by the vaccine itself. 1

Common Adverse Reactions in Children

Local Reactions

• Injection site reactions are the most frequently reported adverse events, occurring in 10-64% of vaccinated children 2
• Pain, tenderness, erythema, and induration/swelling at the injection site typically resolve within 2 days 3, 2
• Redness and pain at injection sites are mild reactions documented across multiple vaccine types 4

Systemic Reactions

Fever:

• Fever is the most common systemic reaction, beginning 6-12 hours post-vaccination and persisting 1-2 days 3, 5
• Age-specific fever rates after influenza vaccination: 11.5% in children aged 1-5 years, 4.6% in children aged 6-10 years, and 5.1% in children aged 11-15 years 3, 5
• Among high-risk children aged 6 months-4 years, fever rates can reach up to 27% 3, 5
• Fever occurs more frequently in children with no prior exposure to vaccine antigens 3, 5

Other Systemic Symptoms:

• Irritability, decreased appetite, and altered sleep patterns (increased or decreased) are common, particularly after pneumococcal conjugate vaccine 3
• Malaise and myalgia typically resolve within 1-2 days 2
• Gastrointestinal symptoms including diarrhea, vomiting, and nausea occur in >1% of vaccinated children 3, 4
• Persistent crying has been reported at a rate of 2.4 per 1000 vaccine doses 6

Serious Adverse Events

Immediate Allergic Reactions:

• Anaphylactic reactions are rare, estimated at approximately 1 per million doses 7
• Immediate hypersensitivity reactions include hives, angioedema, allergic asthma, and systemic anaphylaxis 3, 2
• These reactions likely result from residual egg protein in influenza vaccines or other vaccine components such as gelatin and yeast 3, 7

Neurological Events:

• Febrile seizures have been reported but are uncommon 3
• Hypotonic-hyporesponsive episodes can occur but are rare 3, 7
• Guillain-Barré Syndrome was associated with the 1976 swine influenza vaccine at a rate of <10 cases per 1 million vaccinated, though this association has not been consistently demonstrated with modern vaccines 3, 2

Other Serious Events:

• Extensive limb swelling extending beyond the shoulder or elbow occurs rarely and resembles cellulitis, typically resolving with symptomatic treatment 8
• Bronchiolitis, gastroenteritis, and pneumonia were the most commonly reported serious adverse events after PCV13, though causality was not established 3
• Lymphadenopathy localized to the injection site region has been documented 3

Important Clinical Considerations

Distinguishing True Adverse Reactions from Coincidental Events

• Most respiratory or gastrointestinal symptoms occurring after vaccination represent coincidental illnesses unrelated to the vaccine 9
• Active surveillance studies show that 93.4% of reported AEFIs have a consistent causal association with immunization 6
• Inactivated vaccines contain no live virus and cannot cause the disease they prevent 9

Reporting Requirements

• Healthcare professionals must report ALL clinically significant adverse events to VAERS, even without certainty of causation 3, 5, 2
• Any adverse event resulting in hospitalization, disability, or death requires VAERS reporting 5, 2
• The Institute of Medicine specifically recommends reporting potential neurologic complications including demyelinating disorders 3

Safety Profile Across Vaccine Types

• Large-scale VSD studies of 251,600 children showed no increase in clinically important medically attended events during the 2 weeks after TIV vaccination compared with control periods 3
• PCV13 and PCV7 have comparable safety profiles with no statistically significant differences in serious adverse events 3
• In children with mitochondrial disease, 84% of vaccinations resulted in no AEFI, with no metabolic deterioration or hospitalizations reported 4

Management of Post-Vaccination Fever

• Acetaminophen 10-15 mg/kg every 4-6 hours can be administered for fever or discomfort 5
• Prophylactic acetaminophen is NOT recommended routinely but may be considered for children with a history of seizures or family history of convulsions 5