Monkeypox infection in a smallpox-vaccinated patient

In a recent study published in the Emerging Infectious Diseases journal, researchers at Madigan Army Medical Center assessed the characteristics of monkeypox infection in a patient vaccinated against smallpox.

In Summer 2022, the Centers for Disease Control and Prevention (CDC) initiated an emergency response after the outbreak of monkeypox infections across the US. In addition, on 28 June 2022, the US Department of Health and Human Services (HHS) announced a vaccination strategy against the monkeypox virus to be implemented across the country. 

Research Letter: Monkeypox in Patient Immunized with ACAM2000 Smallpox Vaccine During 2022 Outbreak. Image Credit: Dotted Yeti / ShutterstockResearch Letter: Monkeypox in Patient Immunized with ACAM2000 Smallpox Vaccine During 2022 Outbreak. Image Credit: Dotted Yeti / Shutterstock

Patient characteristics

In the present study, the team reported a patient residing in Washington, USA, who was infected with the monkeypox virus. However, he was successfully vaccinated against smallpox with the ACAM2000 smallpox vaccine eight years before.

The patient was a 34-year-old male who reported having sex with men. He walked into a sexually transmitted infections clinic with a four-day history of malaise, fatigue, and headache with a two-day history of four painless penile lesions. The patient was evaluated at a local emergency department two days before his clinic visit. He tested negative for Chlamydia trachomatis, Neisseria gonorrhea, and herpes simplex virus. While his constitutional symptoms showed improvement over the next two days, his penile ulcers developed into white papular lesions.

The patient reported a history of syphilis and N. gonorrhea in 2017 that was resolved after treatment. His military health records did not show any history of human immunodeficiency virus (HIV) infection or other immunocompromising conditions. He was previously recommended daily treatment with emtricitabine/tenovir as a pre-exposure prophylactic measure against HIV. However, he self-discontinued this treatment a year before he sought medical care. In the past 90 days, the patient stated that he had receptive oral and penetrative anal sexual intercourse with 13 to 14 new partners without any condom usage. His latest sexual encounter was reported 11 days before he sought medical care when he had unprotected anal-insertive sexual intercourse with a single partner at a local Pride event.

Due to his military service, the patient received a smallpox vaccine with ACAM2000 vaccine in March 2014. Furthermore, he denied any recent travel outside Washington or contact with sick individuals.    


The study results showed that the patient displayed four ulcerated penile lesions that had progressed into a patch on the foreskin. This patch was observed two days after the patient developed constitutional symptoms. The lesions were non-tender, with no discharge observed. A tender right inguinal lymph node was also observed, along with a vaccination scar on his right deltoid.

The team noted that the patient tested positive for non-variola orthopoxvirus via polymerase chain reaction (PCR). Subsequent testing showed that the clade II strain caused the infection. However, the patient tested negative for hepatitis C, syphilis, and HIV-1/2 antigen and antibody.

The patient only required supportive care with the administration of oral acetaminophen to treat constitutional symptoms, which resolved ten days after the onset of symptoms. The rash evolved, coalesced, and progressed into a pustule six days after the constitutional symptoms first appeared. The lesion progressed into an ulcer on day 16 before dissipating without causing any residual scarring.

Overall, the study showed that while vaccination was essential in preventing infectious disorders, vaccination alone can prove insufficient in providing immunity against monkeypox infection. Therefore, the researchers believe that vaccination should complement and not replace public health campaigns that facilitate the minimization of high-risk health behaviors.

Journal reference:
Bhavana Kunkalikar

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.


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