Tecovirimat was safe and well-tolerated in a laboratorian who was inadvertently exposed to replication-competent vaccinia virus, according to a case study published in the United States Center for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report.

Vaccinia virus is an orthopoxvirus that is commonly used in the smallpox vaccine, for experimental research and as a vector for novel cancer treatments. Tecovirimat is the first antiviral approved by the US Food and Drug Administration for the treatment of smallpox, and has activity against other orthopoxvirus infections. The CDC has approved an investigational new drug protocol for the use of tecovirimat in the treatment of such infections. Though the Advisory Committee on Immunization Practices recommends smallpox vaccination for all laboratory staff who handle replication-competent vaccinia virus, the CDC was notified about a laboratory work who was unvaccinated and received a needlestick injury.

Therefore, this case report focuses on this previously healthy woman laboratory worker aged 26 years. The patient sustained the needlestick injury to her left index finger from the same needle she used to inject vaccinia virus into the tail of a mouse. The patient was evaluated by 2 community physicians between 2 and 9 days post-infection, both of whom did not recommend contact precaution that prevent auto-inoculation. She had swelling and a single vesicular lesion at the needlestick site when she was evaluated at an occupational health clinic on day 10; the attending physician contacted the CDC and the County of San Diego Health and Human Service Agency. These agencies advised watchful management for worsening infection. By day 12, she was treated at a university-based emergency department for fever, left axillary lymphadenopathy, malaise, pain, and worsening edema of her finger.

The specific strain or concentration of vaccinia virus preparation was not identified as the study sponsor informed investigators that 1 of 2 strains may have been involved and the patient could not recall with strain she handled at the time of injury. As a result of this, and a worsening course of illness with concern for compartment syndrome, the patient was administered a single intravenous dose of vaccinia immunoglobulin 6,000 IU/kg on day 12; this was followed by a twice-daily course of oral tecovirimat 600mg for 14 days. Approximately 48 hours post-treatment initiation, fever and lymphadenopathy resolved and decreases in severity of local pain and edema were observed. Resolution of areas of necrosis at the injury site were not observed until day 94.

Investigators noted that the patient had initially declined vaccination, and during this investigation, she cited concern for adverse events as a result of vaccination and reported that she did not appreciate the extent of infection that could occur when the virus as causes for her decision to not vaccinate. Tecovirimat was well tolerated by the patient with mild side effects. The independent effect of tecovirimat on the clinical course cannot be determined; whether its use should be warranted for similar vaccinia virus infections is not known.

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“This case was the first use of tecovirimat for a laboratory-acquired [vaccinia virus] infection,” the researchers concluded. “Counseling before working with [vaccinia virus] needs to include benefits of vaccination, risks of working with [vaccinia virus] in the laboratory, vaccination-associated adverse events, care of the vaccination site, and contraindications to vaccination… Laboratories need to implement biosafety policies and procedures and ensure that all personnel are adequately trained and aware of the risks associated with the work they perform.”

Reference

Whitehouse ER, Rao AK, Yu YC, et al. Novel Treatment of a Vaccinia Virus Infection from an Occupational Needlestick — San Diego, California, 2019. MMWR Morb Mortal Wkly Rep. 2019;68(42):943-946.