What is the appropriate management for a 37‑week pregnant woman who was exposed to varicella (chickenpox) after her child's exposure at school, has inadvertently received the live attenuated varicella vaccine, and is staying with a relative?

Management of 37-Week Pregnant Woman with Varicella Exposure and Inadvertent Vaccination

Immediate Reassurance Regarding Inadvertent Vaccination

The inadvertent administration of varicella vaccine during pregnancy, while contraindicated, does not warrant termination of pregnancy or excessive concern, as no cases of congenital varicella syndrome have been documented among prospectively reported cases in the pregnancy registry over 10 years of surveillance. 1, 2

• Among 131 live-born infants of seronegative women who received varicella vaccine during pregnancy (82 during the highest-risk first or second trimester), no birth defects consistent with congenital varicella syndrome were documented (prevalence rate = 0%; CI = 0-6.7%). 1
• The three major birth defects reported (prevalence rate = 2.3%) showed no specific pattern and occurred at rates similar to the general U.S. population (3.2%). 1
• The attenuated vaccine virus has lower virulence than wild-type varicella, so theoretical fetal risk, if any, should be even lower than natural infection. 1
• Counseling about potential effects on the fetus is appropriate, but the data strongly support reassurance rather than alarm. 1, 2

Assessment of Current Varicella Immunity Status

Immediately determine the woman's varicella immunity status through history of previous infection, documentation of prior vaccination, or varicella-zoster IgG serology. 3

• If she has a reliable history of chickenpox or documented immunity, she is protected and requires no further intervention for this exposure. 3
• If immunity status is unknown or she is seronegative, proceed with post-exposure prophylaxis protocols below. 3

Post-Exposure Prophylaxis Protocol

If the pregnant woman is seronegative or has unknown immunity status, administer varicella-zoster immune globulin (VZIG) within 96 hours of exposure to prevent severe maternal complications. 1, 4, 3

• The 96-hour window is critical; VZIG effectiveness diminishes significantly after this timeframe. 4
• VZIG may prolong the incubation period by up to one week, extending monitoring from 21 to 28 days after exposure. 4, 5
• VZIG prevents severe maternal disease but does NOT prevent viremia, fetal infection, or congenital varicella syndrome—its primary purpose is maternal protection. 4, 5

If VZIG Window Has Passed or VZIG Is Unavailable

• Consider oral acyclovir prophylaxis for susceptible pregnant women who did not receive VZIG within 96 hours or who have risk factors for severe disease. 6
• If oral acyclovir is used, perform VZV serology so the drug can be discontinued if the patient is seropositive. 1

Monitoring for Varicella Development

Observe the pregnant woman closely for prodromal symptoms (fever, malaise, headache) followed by characteristic vesicular rash for 28 days after exposure (extended from 21 days due to VZIG administration). 4

• Prodromal symptoms typically precede the rash, which characteristically begins on the head and trunk. 4
• If varicella develops, initiate oral acyclovir 800 mg five times daily within 24 hours of rash onset to reduce severity. 4, 3
• For severe complications (particularly pneumonitis), strongly consider hospital admission and intravenous acyclovir 10-15 mg/kg or 500 mg/m² IV every 8 hours for 5-10 days. 3

Management of the Relative Living with the Pregnant Woman

The relative should receive varicella vaccination if they are non-immune and have no contraindications, as household contacts of pregnant women should be vaccinated to create a protective barrier. 7

• MMR and varicella vaccines do not transmit vaccine viruses to contacts in clinically significant ways. 7
• Transmission of varicella vaccine virus to contacts is an extremely rare event. 7
• If a varicella-like rash develops in the vaccinated contact, the risk of transmission is minimal unless vesicles develop at the injection site. 7
• In the rare case of vesicles at the injection site, isolate the vaccinated individual and consider VZIG prophylaxis for the pregnant woman. 7

Critical Considerations at 37 Weeks Gestation

At 37 weeks gestation, the highest-risk scenario is if the pregnant woman develops varicella rash between 5 days before delivery and 2 days after delivery. 4, 5, 3

• This timing results in neonatal exposure without adequate transplacental maternal antibody transfer. 5
• Historical mortality rates in this population reached 31% without intervention. 5
• Immediately inform neonatal healthcare providers if maternal varicella develops in this critical window. 3

Neonatal Management Protocol

• Administer VZIG to the neonate immediately after birth if maternal varicella onset occurs between 5 days before and 2 days after delivery, regardless of whether the mother received VZIG. 5, 3
• Neonatal VZIG dosing: 125 units per 10 kg body weight (maximum 625 units). 5
• If neonatal varicella develops despite VZIG prophylaxis, initiate intravenous acyclovir 10 mg/kg IV every 8 hours for 10 days immediately. 5
• Treatment is most effective when started within 24 hours of rash onset. 5

Common Pitfalls to Avoid

• Do not delay VZIG administration beyond 96 hours in seronegative or unknown-immunity pregnant women after exposure. 4, 3
• Do not assume VZIG prevents fetal infection—it reduces maternal severity but does not eliminate fetal risk. 4, 5
• Do not withhold vaccination from household contacts due to theoretical transmission concerns—natural infection poses far greater risk. 7
• Do not delay acyclovir if varicella develops—efficacy decreases significantly after 24 hours of rash onset. 4, 5
• Do not forget to inform neonatal providers of peripartum varicella exposure for optimal early neonatal care. 3