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ORIGINAL RESEARCH |
From the Center for Health Studies, Group Health Cooperative, Seattle, Washington; Epidemiology and Surveillance Division, National Immunization Program, and Herpesvirus Section, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia.
Address reprint requests to: Kari Bohlke, ScD, Center For Health Studies, Group Health Cooperative, 1730 Minor Avenue, Suite 1600, Seattle, WA 98101-1448; E-mail: bohlke.k{at}ghc.org.
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ABSTRACT |
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METHODS: We enrolled women identified as varicella seronegative during routine prenatal screening at Group Health Cooperative. Participants received the first dose of varicella vaccine at least 6 weeks postpartum and the second dose at least 4 weeks later. They collected ten breast milk samples after each vaccine dose. Breast milk samples were tested for varicella-zoster virus by polymerase chain reaction (PCR). Serum specimens were collected from the mothers 1 month after each vaccine dose, and peripheral blood from their infants was collected onto filter spots 1 month after the mother’s second dose. These samples were tested for varicella immunoglobulin (Ig) G by whole-virus enzyme-linked immunosorbent assay (ELISA), or by the more sensitive glycoprotein ELISA. When possible, filter spots from the infants were also tested by PCR for the presence of varicella zoster virus deoxyribonucleic acid (DNA).
RESULTS: Twelve women were enrolled; all seroconverted after the first vaccine dose. Varicella DNA was not detected by PCR in any of the 217 postvaccination breast milk specimens. None of the infants was seropositive. Samples from six infants were tested for varicella zoster virus DNA by PCR, and all were negative.
CONCLUSION: We found no evidence of varicella vaccine virus excretion in breast milk. These findings suggest that postpartum vaccination of varicella-susceptible women need not be delayed because of breast-feeding.
Varicella infection among adults is typically more severe than infection among children, and is associated with a higher rate of hospitalization1,2 and death.3 Varicella during pregnancy can result in congenital varicella syndrome which, although it seems to be a rare occurrence, is a severe condition characterized by scarring, neurologic defects, limb hypoplasia, muscle atrophy, and eye diseases.4,5 Varicella infection late in pregnancy can cause severe disease in the newborn.6 To prevent these complications, the Advisory Committee on Immunization Practices recommends the varicella vaccine for susceptible, nonpregnant women of childbearing age.7
Although varicella-susceptible women ideally would be identified and vaccinated before becoming pregnant, young adults might not have regular preventive care visits and might be difficult to target for screening. In this context, prenatal screening of women with no history of chickenpox offers an alternative means of identifying varicella-susceptible women of childbearing age.8 These women should be vaccinated postpartum.
The varicella vaccine (VARIVAX, Merck & Company Inc., West Point, PA) contains live attenuated virus, and decisions regarding the timing of postpartum vaccination involve consideration of whether the vaccine can safely be administered to breast-feeding women. There is a case report of detection of wild-type varicella zoster virus deoxyribonucleic acid (DNA) in breast milk,9 and detection of other human herpesviruses has also been reported.10–13 Researchers reporting detection of viral antigens in breast milk have interpreted this to signify excretion of the virus in breast milk. However, it is not known whether the varicella vaccine virus is excreted in breast milk, or what the clinical consequences of excretion, if any, would be for the breast-feeding infant. In the case of the rubella vaccine, another live attenuated virus vaccine administered to postpartum women, the vaccine virus is frequently excreted in breast milk but has not been reported to cause clinical illness in the infant or other adverse effects.14
Current varicella vaccine recommendations allow for the vaccination of breast-feeding women,15 but uncertainty as to possible adverse effects might lead some providers to delay vaccination of postpartum women. However, delaying vaccination prolongs the period during which the mother is at risk of acquiring natural varicella infection. If the mother acquires natural varicella, she puts both herself and her infant at risk for complications from the disease, because the mother is likely to transmit the infection to her susceptible infant. To avoid unnecessary delays in vaccination, it is therefore important to gain additional knowledge about the safety of administering the vaccine to breast-feeding women.
The purpose of the present study was to evaluate whether the varicella vaccine virus could be detected in breast milk after vaccination of breast-feeding women, and whether there was serologic evidence of exposure of the infant to varicella virus after maternal vaccination.
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MATERIALS AND METHODS |
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We identified varicella-seronegative women, tested during prenatal screening from February 1999 to December 2001, through Group Health Cooperative’s automated laboratory and health care encounter data sets. Prenatal varicella immunity screening was conducted by the Group Health laboratory with a commercial enzyme immunoassay. We restricted enrollment to women 18 years of age or older at study entry, who agreed to be vaccinated while breast-feeding and planned to breast-feed for at least 1 month after the first vaccine dose, and who did not have contraindications to the varicella vaccine. To ensure that women were seronegative at the time of study entry, confirmatory testing of potentially eligible subjects was conducted. Blood specimens were sent to the National Varicella Zoster Virus Laboratory of the Centers for Disease Control and Prevention (CDC) for whole-virus varicella zoster virus enzyme-linked immunosorbent assay (ELISA) testing for detection of varicella zoster virus immunoglobulin (Ig)G antibodies in serum. With one exception, only women who were varicella seronegative on this confirmatory test were enrolled in the study. The exception was a woman who had received her first dose of varicella vaccine before being contacted by us for the study. This woman seroconverted after that vaccination but was enrolled, and we provided her second dose of vaccine as part of the study.
Before we administered the first dose of vaccine, women had to meet the following additional criteria: 1) no exposure to a person with chickenpox or herpes zoster in the previous 4 weeks, 2) no receipt of blood or blood products in the previous 4 weeks, and none expected in the subsequent 10 weeks, 3) no receipt of another live viral vaccine in the previous 30 days, and 4) no household members vaccinated with the varicella vaccine in the previous 3 months. Furthermore, their infants had to be at least 6 weeks of age, immunocompetent, and not exposed in the previous 4 weeks to a person with chickenpox or herpes zoster. Women with infants less than 6 months of age were vaccinated only if the infant had been at least 36 weeks’ gestation and at least 2500 g at birth. All participants signed an informed consent form that had been approved by Group Health Cooperative and CDC institutional review boards. The consent form indicated our uncertainty as to whether the vaccine virus would be excreted in breast milk, as well as our uncertainty as to what effect excretion might have on the infant.
Eligible women received their first dose of varicella vaccine no earlier than 6 weeks postpartum. The second vaccine dose was administered approximately 4 weeks after the first dose (Figure 1
). The decision to vaccinate no earlier than 6 weeks postpartum was based on Group Health Cooperative’s current varicella vaccination policy, which was developed before this study.
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Serum was collected from each participating mother 1 month after each vaccine dose. Filter spot specimens were obtained from the infants approximately 1 month after the mother’s second vaccine dose. All blood specimens were tested for varicella-specific IgG with a whole-virus varicella zoster virus ELISA (CDC).21 For mothers with negative or equivocal IgG results after vaccination, specimens were retested with a more sensitive glycoprotein ELISA (CDC assay, varicella zoster virus glycoprotein reagent provided by Merck & Company).22 Seropositivity was defined as an optical density (OD) of greater than 0.165 for the whole-virus ELISA assays, and 0.15 for the glycoprotein ELISA assay. Cut-off values were determined empirically for each of the two serologic protocols by analysis of multiple sources of assay variance (interoperator, day-to-day, sample-to-sample) on specimens with established varicella zoster virus serologic status (strong positive, weak positive, negative). The cut-off value for positivity is based on the mean OD for eight varicella zoster virus–negative specimens tested on 3 days by two operators, plus 3 standard deviations (cumulative variance).
For six of the 12 infants, we also tested the filter spot blood specimen by PCR for the presence of varicella zoster virus DNA. For the other six infants, there was inadequate specimen remaining, and we were not able to conduct PCR. For the PCR tests conducted, filter spot specimens were punched out, rehydrated with 500 µL of sterile phosphate-buffered saline, and soaked for 30 minutes at ambient temperature. The filter spot was transferred along with the elution fluid into the barrel of a 3.0-mL syringe inserted into a sterile 15-mL conical centrifuge tube and centrifuged at 2000 rpm for 20 minutes. Total DNA from the resulting pellet was isolated with NucleoSpin Tissue Kits (CLONTECH Laboratories Inc) according to the manufacturer’s instructions. Deoxyribonucleic acid from an individual specimen was usually recovered in a final volume of 200 µL of molecular-grade water or 10 mmol/L Tris (pH 8.0). The DNA was tested with four real-time PCR and/or four conventional PCR assays in combination with restriction fragment length polymorphism analysis, as described for the breast milk specimens.
Participants were asked to report any rash lesions on themselves or their infants from the time of the first vaccine dose until 6 weeks after the second vaccine dose. In addition, the study nurse contacted study participants by telephone at 2 and 6 weeks after each vaccine dose to determine whether a rash had occurred. If the woman reported a rash that included vesicular lesions, the lesions were tested for the presence of varicella zoster virus DNA. Samples were collected by unroofing and scraping vesicles with a polyester-tipped swab, which was then smeared on a glass microscope slide. Additional material was collected by pressing another slide onto unroofed lesions, and by abrading the lesions with the edge of the slide. The swabs and slides were transported to the CDC at ambient temperature. Deoxyribonucleic acid was extracted from these specimens and was tested with the same varicella zoster virus PCR protocols detailed above.
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RESULTS |
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). Among the six infants who had blood specimens tested by PCR for varicella zoster virus DNA, all six were negative (data not shown).
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DISCUSSION |
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Our findings contrast with those for rubella vaccine, the only other live virus vaccine (administered as part of the measles–mumps–rubella vaccine) routinely administered to postpartum women. Buimovici-Klein et al23 isolated rubella virus in a breast milk sample collected 12 days after rubella vaccination. In a larger study by Losonsky et al,14 breast milk samples were collected "at frequent intervals" from 16 women who had been vaccinated against rubella at 2–4 days postpartum, and rubella virus was isolated by culture from the breast milk of 11 of 16 (68%) of the women. For the most part, virus was detected during the first 2 to 3 weeks after vaccination, although in one woman shedding continued for 34 days. Breast milk specimens in the current study were also collected during the first 3 weeks after vaccination, but we detected no varicella vaccine virus in the milk specimens. Four of the 16 infants in the Losonsky study seroconverted, but none developed clinically apparent illness. The mothers of all four of these infants had detectable rubella virus in breast milk and nasopharyngeal secretions. The IgG antibody response in these four infants was transient; titers peaked at 4–8 weeks after the mother’s vaccination and were undetectable after 18–20 weeks. The timing of the peak antibody response in the infants in the Losonsky study corresponds to the timing of blood specimen collection from the infants in the current study, but none of the infants in the current study demonstrated a varicella IgG antibody response.
Viral excretion in breast milk can occur after infection with a number of human pathogens, including human immunodeficiency virus type 1,24 human T-cell lymphotrophic virus type I,25 rubella virus,26 cytomegalovirus,10,11 Epstein-Barr virus,13 and herpes simplex virus.12,27 These studies identified virus in breast milk with PCR,10,11,24 culture,11,25–27 or a DNA–DNA hybridization assay.12,13 Cytomegalovirus, Epstein-Barr virus, and herpes simplex virus are human herpesviruses, as is varicella zoster virus. There has been a report of detection of wild-type varicella zoster virus in breast milk. In that study, varicella zoster virus was detected by PCR in breast milk samples "obtained on the third day after onset and subsequently" from a woman with active chickenpox.9 The breast-feeding infant developed chickenpox 16 days after disease onset in the mother. Although it is possible that varicella zoster virus was transmitted through breast milk in this case, it also possible that the disease was transmitted from the mother by the respiratory route or by direct contact with lesions. Furthermore, the presence of active disease during the collection of the breast milk specimens raises the possibility of inadvertent contamination of the specimens.28
If varicella vaccine virus were present in breast milk specimens collected from our study participants, the specimen collection and laboratory methods used in this study should have been sufficiently rigorous to ensure detection. Mothers participating in the study collected ten breast milk samples on days 3–21 after each vaccine dose. This time period spans the average incubation period of 10–21 days for natural varicella infection.16 Because we collected samples after each vaccine dose, we would have been able to detect excretion occurring as late as 7 weeks after the first vaccine dose (the last breast milk sample was collected 3 weeks after dose 2, which was administered roughly 4 weeks after dose 1). Furthermore, the every-other-day sample collection schedule increased the likelihood of detecting transient excretion. Finally, each of the eight PCR assay protocols performed were sensitive enough to reliably detect varicella zoster virus DNA levels as low as 10–100 copies per sample.17 Polymerase chain reaction was preferable to culture for this study because it is the most sensitive assay and can detect both viable and nonviable virus. The freezing and thawing of the breast milk samples would likely have eliminated the majority, if not all viable virus in these samples.
The sample size for this study, although small, was adequate to detect excretion of virus in at least one subject, if the varicella vaccine virus were excreted with a similar frequency as the rubella vaccine virus in the Losonsky study.14 Assuming a binomial distribution, if 68% of vaccinated breast-feeding women excrete virus, a sample size of 12 women would give almost 100% probability of observing excretion in at least one subject. Even if as few as 13% of vaccinated women excrete virus, we would have had more than 80% probability of observing excretion in at least one subject. Based on the upper limit of the confidence interval for our estimated proportion of women excreting virus, the highest proportion consistent with our data is 0.27. Thus, although we cannot rule out the possibility that excretion of the varicella vaccine virus does occur, these data suggest that if it occurs, it occurs less frequently than rubella vaccine virus excretion.
Although data are not convincing that wild-type varicella zoster virus is excreted in breast milk, we postulate the following reasons why the vaccine strain might be less likely than wild-type varicella zoster virus to be excreted. Lower viral load or lower viremia after vaccination might reduce the likelihood of excretion in breast milk. A 1985 study of children exposed to wild-type varicella or the Oka vaccine strain virus reported viremia among the naturally infected children who developed chickenpox but not among the vaccinated children.29 In cytomegalovirus,30 human T lymphotropic virus type 1,31 and human immunodeficiency virus type 132 infections, viral load in breast milk30,32 or peripheral blood31 seems to increase the risk of transmission of the infection from mother to child.
Our study was not designed to address transmission of the vaccine virus by a means other than breast milk. Because such transmission seems to be quite rare after vaccination of healthy persons, it is unlikely that we would have detected it in this study, although it has been reported by others. In one instance, a healthy 38-year-old woman with 30 postvaccination lesions (25 of which were vesicular) transmitted the varicella vaccine virus to her two children.33 In another instance, a vaccinated toddler with 30 vesicular lesions transmitted the virus to his pregnant mother.34 A proposed mechanism for transmission of the vaccine virus involves spread from post-vaccination rash lesions, with a greater number of lesions increasing the risk of transmission.35 A generalized rash (ie, a rash beyond the injection site) consisting of a median number of five lesions occurs in 5.5% of adults after the first vaccine dose and in 0.9% after the second vaccine dose (Merck & Company Inc., package insert). Most healthy adults, therefore, do not develop a generalized rash after vaccination, and those who do are likely to have fewer lesions than the vaccinees who transmitted the virus, described above. Therefore, although it is possible for a vaccinated mother to transmit the vaccine virus to her infant independently of breast-feeding, this is likely to be a very rare event.
When deciding when to vaccinate women postpartum, the small risk of transmitting the vaccine virus must be balanced against the benefit of earlier protection of the mother. If the mother develops natural varicella, not only is she at risk for complications from the illness, but she also has a high probability of transmitting the wild-type virus to her susceptible infant. Transmission of chickenpox to an infant can have serious consequences. A study of varicella mortality in the United States found that during 1990–1994, infants less than 12 months of age had a case fatality rate that was four times higher than the case fatality rate among children 1–4 years of age.3 In addition, if a woman becomes pregnant again before vaccination, she and her subsequent fetus are at risk for the consequences of varicella during pregnancy. Finally, compliance with the two-dose vaccine schedule might increase if women received their first dose soon after delivery and their second dose at their 6-week postpartum visit; women would be targeted for vaccination at a time when they are in contact with the health care system, and before they transition to other providers for their health care needs.
In summary, especially as varicella epidemiology changes with implementation of a vaccination program, varicella-susceptible women of childbearing age are a priority for varicella vaccination efforts. Health care providers should inform women identified as varicella susceptible during pregnancy of the need to avoid exposure during pregnancy and obtain vaccination after delivery. In this study of 12 women who received the varicella vaccine while breast-feeding, we detected no varicella zoster virus in a total of 217 breast milk samples collected after both vaccine doses. Although we cannot completely exclude the possibility that excretion occurs, these findings suggest that vaccination should not be delayed in breast-feeding women who are known to be varicella susceptible. Offering the first vaccine dose before a susceptible woman is discharged after delivery and the second dose at the postpartum follow-up visit would provide early protection for the woman and would facilitate compliance with the two-dose vaccine schedule.
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Footnotes |
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This publication was supported by Grant/Cooperative Agreement number UR6CCU017728-01 from the Centers for Disease Control and Prevention (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent official views of CDC.
The authors thank Barbara Carste, MPH, for data management, and Martha L. Thieme, Denise R. Brown, and Marlene DeLeon for technical laboratory assistance.
doi:10.1016/S0029-7844(03)00860-3
Received April 30, 2003. Received in revised form July 9, 2003. Accepted July 17, 2003.
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