August 30, 2019
By Marilynn Larkin
NEW YORK (Reuters Health) - Vaccinated individuals are unlikely to transmit the vaccine-strain varicella-zoster virus (Oka strain; vOka) to others and might do so only if a rash is present, a systematic review reveals.
The review "indicates that transmission of vaccine virus from healthy vaccine recipients is very rare," Dr. Mona Marin of the US Centers for Disease Control and Prevention in Atlanta told Reuters Health. "To date, only 13 cases from 11 vaccinated, immunocompetent persons have been reported, all after receipt of the first dose of varicella vaccine, and most commonly among household contacts."
"Transmission of the vaccine virus resulting in clinical varicella was only reported from vaccine recipients who developed a rash after vaccination, and cases of varicella caused by the vaccine strains have typically been mild," she noted by email "Healthy, varicella-vaccinated persons have minimal risk for transmitting the vaccine strain to contacts, and only if a rash is present."
Dr. Marin and colleagues reviewed the literature through 2018 for articles on vOka transmission from individuals who received vaccines containing the live-attenuated varicella-zoster virus. Data were abstracted data to describe vOka transmission by the index patient's immune status, type (varicella or herpes zoster) and severity of illness, and whether transmission was laboratory-confirmed.
As reported online August 30 in Pediatrics, 20 articles were included in the analysis. As Dr. Marin noted, 13 patients contracted vOka varicella after transmission from 11 immunocompetent varicella vaccine recipients. In all cases, the vaccine recipient had a rash: six varicella-like and five herpes zoster.
Transmission was mostly to household contacts. One additional case was not considered direct transmission from a vaccine recipient, but the mechanism was uncertain.
Further, transmission from vaccinated immunocompromised children also occurred only if the vaccine recipient developed a rash following vaccination.
The secondary cases of varicella caused by vOka were mild.
The authors acknowledge a limitation of the study, in that other vOka transmission cases are likely to have occurred but not been unpublished.
Nonetheless, Dr. Marin said, "The findings support the existing recommendations for routine varicella vaccination and the guidance that persons with vaccine-related rash avoid contact for the duration of the rash with persons not immune to varicella who are at high risk for severe complications."
Dr. Betsy Herold, Chief, Division of Pediatric Infectious Diseases, Children's Hospital at Montefiore in New York City, commented, "The findings are not surprising and are consistent with current understanding of the safety of the varicella vaccine."
Like Dr. Marin, she noted, "the risk of transmitting vaccine virus from healthy vaccinated individuals is low, but persons who develop a rash following vaccination may be infectious and should avoid contact with high-risk contacts, such as patients with cancer, transplant recipients, patients on immunosuppressive therapy or with underlying immunodeficiencies."
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