Contents

21 Varicella (chickenpox)

21.8 Public health measures

At present, VZV is not a notifiable disease.

21.8.1 Susceptibility

In general, a positive past history of chickenpox can be taken as indicating immunity, provided there has not been an intervening bone marrow transplant or other immunosuppressive therapy. Maternal recall of varicella or characteristic rash is reliable evidence of immunity. In people with no history or recall of the rash, 70–90 percent are found to be immune.24 Consult with the local laboratory about the availability and interpretation of tests.

21.8.2 Post-exposure prophylaxis with zoster immunoglobulin (ZIG)Top

ZIG is a high-titre immunoglobulin (IG) available from the New Zealand Blood Service for passive immunisation of varicella in high-risk individuals. It is most effective if given as soon as possible after exposure, but may be given up to 10 days post-exposure.26, 27 Intravenous IG (IVIG) can be given when ZIG is unavailable.

The decision whether to offer ZIG depends on:

Contact (exposure) can be defined as follows:

Provided exposure has occurred and susceptibility is likely, ZIG is recommended for:

Dosage of ZIG

The ZIG prepared by CSL Behring in Melbourne, from New Zealand donors, is available in single vials containing 200 IU varicella-zoster antibody. The actual volume in the vial is stated on the label. The recommended dose is based on body weight and is shown in Table 21.2 below. ZIG should be given intramuscularly, not intravenously. 

Table 21.2: Dose of ZIG based on body weight​

Weight of patient (kg) Dose (IU) Number of vials​
0–10 125 1
10.1–20 250 2
20.1–30 375 2
30.1–40 500 3
over 40    600 3

Source: CSL Behring. 2014. Zoster Immunoglobulin-VF Product Data Sheet. URL: www.nzblood.co.nz/Clinical-information/Transfusion-medicine/Health-professionals-medicine-datasheets/Immunoglobulins (accessed 24 June 2015).

If ZIG is not available, IVIG can be used. The titre of anti-varicella antibody will vary between lots and the blood transfusion centre haematologist needs to be contacted to confirm the appropriate dose when IVIG is used.

21.8.3 In-hospital exposureTop

In the event of an exposure:

Varicella vaccine is funded for post-exposure prophylaxis of immune competent in-patients who are susceptible to varicella.

21.8.4 Exclusion from school or early childhood education servicesTop

Parents/guardians should be advised that:

21.8.5 Post-exposure vaccination and outbreak controlTop

Varicella vaccine may be used for post-exposure prophylaxis. Data from the US and Japan from household, hospital and community settings indicates that the varicella vaccine is effective in preventing illness or modifying varicella severity if used within three days, and possibly up to five days, of exposure. The US Advisory Committee on Immunization Practices (ACIP) recommends the vaccine for use in susceptible individuals following exposure to varicella.9

Varicella vaccine is funded for post-exposure prophylaxis of immune competent in-patients who are susceptible to varicella.

If exposure to varicella does not result in infection, post-exposure vaccination should induce protection against subsequent exposure. If the exposure results in infection, no evidence indicates that administration of the varicella vaccine during the pre-symptomatic or prodromal stage of illness increases the risk for adverse events following immunisation. Note that although this method of immunisation may be successful, it is not necessarily reliable.28 Immunisation before exposure is therefore recommended as the preferred method of preventing outbreaks.

21.8.6 Care of pregnant women after exposureTop

Pregnant women are at higher risk of severe complications from varicella. If an immune-competent pregnant woman is exposed to varicella, it is recommended, where possible, that her varicella antibodies be assessed if she has no history of varicella (Figure 21.2). If there is no evidence of immunity, two possible courses of action are available: either administer ZIG, or await the onset of symptoms and as soon as possible commence the administration of acyclovir, which is effective in this situation and now regarded as safe in pregnancy. Discuss the clinical circumstances with an infectious diseases physician before deciding on which course of action is best.

Intravenous acyclovir is recommended for the pregnant woman with severe complications of varicella. ZIG given to a pregnant woman within five days of delivery may not protect the fetus/neonate. The neonate should receive ZIG on delivery and may need treatment with acyclovir (Figure 21.3).

Figure 21.2: Management of pregnant women exposed to varicella or zoster

Every effort should be made to confirm the diagnosis in the suspected positive contact and assess significance of exposure.a Exposure or symptoms in the final two weeks of pregnancy should always be discussed with a specialist.

Figure 21.2: Management of pregnant women exposed to varicella or zoster

a Exposure to varicella or zoster for which ZIG is indicated for susceptible persons includes: living in the same household as a person with active chickenpox or herpes zoster; face-to-face contact with a case of chickenpox for at least 5 minutes; close contact (eg, touching, hugging) with a person with active zoster.
b Efficacy of acyclovir for post-exposure prophylaxis has not been tested in controlled trials. Dose is 800 mg orally, 5 times per day for 7 days.
c The mother is at risk of pneumonitis if: in second half of pregnancy; has underlying lung disease; is immune compromised; is a smoker.

Source: adapted from Palasanthiran P, Starr M, Jones C (eds). 2002. Management of Perinatal Infections. Sydney: Australian Society for Infectious Diseases. (Under review.)

Pregnant women exposed to VZV should be counselled about the risks of congenital varicella syndrome (CVS), a rare but devastating disorder that can occur following varicella zoster infection during pregnancy (see Table 21.3). The risk of CVS is greatest in the first 20 weeks of pregnancy. Large case studies suggest that the rate of CVS is 0.4 percent when maternal infection occurs up to week 12 of pregnancy, and 2 percent from weeks 13 to 20.

There is no single diagnostic test available for CVS. Regular fetal ultrasound for developing anomalies is recommended. VZV fetal serology is unhelpful but amniocentesis may be considered; negative VZV PCR may be reassuring.

Table 21.3: Sequelae of congenital varicella

Sequelae Frequency
Skin scars 78%
Eye abnormalities 60%
Limb abnormalities 68%
Prematurity, low birthweight 50%
Cortical atrophy, severe developmental delay 46%
Poor sphincter control 32%
Early death 29%

Source: adapted from Palasanthiran P, Starr M, Jones C (eds). 2002. Management of Perinatal Infections. Sydney: Australian Society for Infectious Diseases. (Under review.)

Figure 21.3: Management of infants from mothers with perinatal varicella or zoster

Figure 21.3: Management of infants from mothers with perinatal varicella or zoster

Notes
  • Transplacentally acquired VZV is high-risk and severity is reduced by ZIG.
  • ​ZIG is not always effective in preventing severe disease.

Source: adapted from Palasanthiran P, Starr M, Jones C (eds). 2002. Management of Perinatal Infections. Sydney: Australian Society for Infectious Diseases. (Under review.)

For more details on control measures, refer to the Control of Communicable Diseases Manual.29