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MPXV Transmission Following receipt of a Single Dose of JYNNEOS Vaccine
What Happened: A Breakthrough Infection
In September 2023, a 31-year-old male healthcare worker in New York City contracted monkeypox (MPXV) despite having received a single dose of the JYNNEOS vaccine approximately four months prior. The patient worked in a hospital setting and had direct contact with a patient confirmed to have MPXV. He developed symptoms – a lesion on his forearm – nine days after the exposure.
The patient’s medical history was unremarkable, with no known immunocompromising conditions. He reported no prior history of smallpox vaccination. He adhered to recommended personal protective equipment (PPE) protocols, but the report details a potential lapse in full adherence during a prolonged interaction with the infected patient.
Diagnostic testing confirmed the presence of MPXV DNA in the lesion sample via polymerase chain reaction (PCR). Viral sequencing identified the virus as belonging to clade IIb, the predominant strain circulating during the 2022-2023 outbreak.
Understanding the JYNNEOS Vaccine and MPXV Clades
JYNNEOS is a live,attenuated vaccine approved for the prevention of both smallpox and MPXV. Its administered as a two-dose series, typically 28 days apart. However, during the 2022-2023 outbreak, a single-dose strategy was implemented to maximize coverage due to vaccine supply limitations.
The effectiveness of JYNNEOS varies depending on the MPXV clade. Early data suggested high efficacy against Clade I, historically the dominant strain in central Africa. However, the 2022-2023 outbreak was primarily driven by Clade IIb, and data on JYNNEOS’s effectiveness against this clade, especially with a single dose, was less robust.
This case underscores that a single dose of JYNNEOS may not provide complete protection against MPXV infection, especially with exposure to Clade IIb. The patient’s infection highlights the importance of completing the two-dose series when feasible and maintaining strict adherence to PPE guidelines, even after vaccination.
Who is affected and What Does This Mean?
This case has implications for healthcare workers, individuals at high risk of MPXV exposure (including men who have sex with men), and public health officials. It reinforces the need for a multi-layered approach to MPXV prevention, including vaccination, PPE, and awareness of potential exposure risks.
The incident also raises questions about the optimal vaccination strategy. While a single dose provided some level of protection during the outbreak, the possibility of breakthrough infections suggests that completing the two-dose series is crucial for maximizing immunity. Further research is needed to determine whether booster doses are necessary to maintain long-term protection, particularly against evolving viral strains.
The patient in this case experienced a relatively mild illness, suggesting that the vaccine may have mitigated the severity of the infection. However, even mild cases can contribute to ongoing transmission, emphasizing the importance of prompt diagnosis and isolation.
Timeline of Events
- September 2023: Healthcare worker exposed to MPXV through patient contact.
- Approximately 4 months prior: Healthcare worker received a single dose of JYNNEOS vaccine.
- 9 days post-exposure: Development of a lesion