What vaccine is associated with the highest number of adverse effects?

Vaccine with Highest Adverse Effects

The HPV vaccine (Cervarix) has the highest reported rate of injection site adverse events among vaccines, with 94% of recipients experiencing local reactions compared to 88% in placebo recipients. 1

Comparison of Adverse Event Profiles Among Vaccines

HPV Vaccines (Cervarix and Gardasil)

Both HPV vaccines demonstrate significant rates of adverse effects, particularly local reactions:

• Cervarix (Bivalent HPV vaccine):

  • Injection site adverse events in 94% of recipients vs 88% in placebo 1
  • Systemic adverse events in 86% of recipients 1
  • Fever (≥100°F/37.5°C) in 16.6% of recipients vs 13.6% in placebo 1

• Gardasil (Quadrivalent HPV vaccine):

  • Injection site adverse events in 83.9% of recipients 1
  • Pain reported by 83.9% of vaccinees vs 75.4% in aluminum-containing placebo 1
  • Severe pain, swelling, or erythema in 2.8%, 2.0%, and 0.9% of recipients, respectively 1

Age-Related Differences in HPV Vaccine Adverse Events

Research shows significant age-related differences in adverse event reporting:

• Preteens and teens are more likely to report vaccine adverse events than adults 2
• 78% of participants reported pain at the injection site 2
• 17% reported injection site bruising or discoloration 2
• 15% reported presyncope or syncope (fainting) 2

Japanese Encephalitis Vaccine (JE-VC)

For comparison, JE-VC demonstrates a lower overall adverse event profile:

• Most common local reactions: pain and tenderness in adults; redness in children aged 2 months to <3 years 1
• Most common systemic reactions: headache and myalgia in adults; fever in children 1

Serious Adverse Events

HPV Vaccines

• Vaccine-related serious adverse events occurred in <0.1% of persons receiving quadrivalent HPV vaccine 1
• Five serious adverse events reported with Gardasil included: bronchospasm, gastroenteritis, headache/hypertension, vaginal hemorrhage, and injection site pain/movement impairment 1
• In a critical review, some studies found more severe adverse events in the HPV vaccine arm compared to placebo 3

Pregnancy Considerations

• Among women becoming pregnant within 30 days of HPV vaccination, 5 delivered infants with congenital anomalies, compared to none in the placebo group 1
• However, these anomalies were unrelated in type and judged by expert review not likely related to the vaccine 1
• For women becoming pregnant beyond 30 days after vaccination, 10 Gardasil and 16 placebo recipients had pregnancies with congenital anomalies 1

Mitigating Adverse Effects

Research suggests that exercise may help reduce adverse reactions following vaccination:

• A 15-minute bout of upper body exercise before HPV vaccination resulted in significantly fewer days of tenderness in female adolescents 4
• Exercise groups reported reduced days of swelling, fever, and lowered appetite across both genders 4

Clinical Implications

When administering vaccines with higher rates of adverse effects:

1. Provide thorough pre-vaccination counseling about expected adverse effects
2. Consider age-appropriate education, as knowledge and attitudes about HPV and vaccination vary by age 2
3. Implement syncope precautions for adolescents receiving HPV vaccines due to higher rates of presyncope/syncope
4. Consider incorporating brief exercise before vaccination to potentially reduce adverse reactions 4
5. Monitor for 15 minutes post-vaccination to address immediate adverse reactions

While HPV vaccines have higher rates of adverse effects compared to other vaccines, it's important to note that most adverse events are mild to moderate and self-limiting, and the overall safety profile supports the positive risk-benefit ratio of vaccination 5.