Realizing you have just accidentally added the wrong sample into your test tube is a gut-wrenching frustration lab workers are used to, but imagine looking down and realizing that, rather than inoculating an animal, you have just stabbed yourself in the hand with an infected needle. Whoops.

That’s what happened two years ago to a virologist working in a poxvirus lab in Boston, according to a recent report by the CDC. The needle he jabbed himself with was being used to infect mice with vaccinia virus, a human pathogen belonging to the same family of viruses as smallpox and cowpox. Although vaccinia tends to only cause mild symptoms, unlike smallpox, the case was interesting because he had recently been vaccinated against the virus in case of such laboratory blunders occurring.

According to the case report, which has been published in the Morbidity and Mortality Weekly Report, back in November of 2013, a 27-year-old poxvirus researcher was conducting an experiment which involved infecting anesthetized mice with vaccinia virus, the agent used to create the smallpox vaccine due to close similarities between the viruses. As he was about to scratch, or scarify, the mouse with the needle, he became distracted (happens to the best of us) by another mouse in a different cage and consequently accidentally stabbed himself in the left thumb. The needle made its way through two pairs of gloves and punctured his skin, causing him to bleed.

Shortly after the incident, the man developed a skin rash on his left arm, so he made his way to the local emergency department where he was diagnosed with a common skin infection called cellulitis, which affects the deeper layers of the skin and underlying tissue. He was prescribed antibiotics to treat the infection and discharged, but the following day he returned to his institution’s occupational health clinic with a necrotic, or dying, lesion at the site he stabbed himself. It then became apparent that the man was infected with the vaccinia virus, despite the fact that he had been vaccinated that same year. The dying tissue on his thumb was then surgically removed, and his symptoms resolved over the following month.

This case has sparked interest because at the time of vaccination, the man seemed to respond as though it had been successful- he developed a small white lesion at the injection site, which is usually indicative of an immune response. Furthermore, blood tests showed that he had elevated levels of antibodies, which would indicate either vaccination or infection. That being said, the level of antibody in the body required to protect against infection is unknown. It’s therefore possible that vaccination prompted a sufficient immune response to reduce the severity of his symptoms, but not enough to protect him from infection.

Although two other cases of lab-acquired vaccinia virus infection have been reported previously, one of the individuals was vaccinated ten years prior to the incident, and the other did not show signs of vaccine take at the time of immunization.  

[Via Morbidity and Mortality Weekly Report and Live Science]