Can the varicella (chickenpox) vaccine prevent varicella infection in healthy individuals?

Can Varicella Vaccine Prevent Chickenpox Infection?

Yes, varicella vaccine is highly effective at preventing chickenpox infection in healthy individuals, with one dose providing approximately 85% protection against any varicella disease and over 95% protection against severe disease, while two doses increase efficacy to 92-98%. 1

Vaccine Efficacy by Dosing Schedule

Single-Dose Protection

• One dose of varicella vaccine provides approximately 85% effectiveness in preventing any varicella infection in healthy children 1
• Single-dose vaccination is over 95% effective in preventing severe varicella disease, even when breakthrough infections occur 1
• After one dose, 76-85% of children achieve protective antibody levels 1
• In adults, single-dose protection is lower at approximately 70%, compared to over 90% in children 2, 3

Two-Dose Protection (Current Standard)

• Two doses of varicella vaccine provide 92-98% effectiveness against any varicella disease 1
• Recipients of two doses are 3.3-fold less likely to develop breakthrough varicella compared to one-dose recipients 1
• After two doses, over 99% of children achieve protective antibody levels, compared to 76-85% after a single dose 1
• Two-dose vaccination provides 100% efficacy against severe disease 1

Real-World Population Impact

• A 14-year prospective cohort study demonstrated sustained vaccine effectiveness of 90% with no evidence of waning immunity over time 4
• Varicella incidence decreased nine- to tenfold compared to the prevaccine era in vaccinated populations 4
• Since implementation of the vaccination program in 1995, varicella incidence, hospitalizations, and deaths have declined substantially in the United States 1

Post-Exposure Prophylaxis Efficacy

The vaccine also works as post-exposure prophylaxis when given promptly after exposure:

• Vaccination within 3 days of exposure is over 90% effective in preventing varicella infection 1, 5
• Vaccination within 5 days of exposure is approximately 70% effective in preventing varicella and 100% effective in preventing severe disease 1, 5
• Post-exposure vaccination should be offered to all unvaccinated persons without evidence of immunity, including both children and adults 1, 5

Breakthrough Infections

When breakthrough varicella occurs in vaccinated individuals, the disease is typically modified:

• Breakthrough cases usually present with fewer than 50 lesions (compared to 250-500 in unvaccinated persons) 1
• Breakthrough disease has shorter duration and lower fever than cases in unvaccinated individuals 1
• Most breakthrough cases occur early after vaccination, particularly in one-dose recipients 4
• No children developed varicella after receiving a second dose in long-term follow-up studies 4

Important Clinical Caveats

• The vaccine is licensed for healthy persons aged 12 months and older 1
• Efficacy is lower in adults (approximately 70%) compared to children (over 90%), though adults still benefit significantly from vaccination 2, 3
• Immunocompromised individuals may have reduced vaccine response and require special consideration 1
• The vaccine prevents not only infection but also reduces the risk of herpes zoster (shingles) later in life compared to natural infection 4