2nd Monkeypox Vaccination Needed to Prevent Breakthrough Infections

A recent non-peer-reviewed study conducted in Paris, France, describes the outcomes of high-risk contacts receiving the third-generation IMVANEX® (Jynneos) vaccine as an early postexposure ring vaccination (EPRV) and potential monkeypox virus (MPXV) breakthrough infections after the first dose.

In this cohort of 276 individuals vaccinated with IMVANEX at the Bichat Claude Bernard University Hospital between May 27 and July 13, 2022, 4% (12) of the participants had MPXV breakthrough infections.

Ten of these 12 patients developed an MPXV infection in the five days following the first vaccination, and two others had a breakthrough infection at 22 and 25 days.

Ten other patients declared skin lesions compatible with an MPXV infection on the study questionnaire.

However, six had a negative PCR, and four declined to return to the center for PCR testing.

Since the incubation of the MPXV has been described to range from 5 to 21 days, delaying the second vaccination may be too late to prevent the disease in some patients, stated these researchers on August 4, 2022.

'A previous phase 1 study found that with a single dose of the IMVANEX (MVA) smallpox vaccine in humans, the peak of antibody titer was reached at day 14 with a decrease of antibodies until the second dose of vaccine.'

Therefore, the fact that 10 out of 12 cases occurred five days after vaccination is not surprising.

We were more surprised by the two cases in which the infection occurred after 20 days.

Whether the decrease of antibodies from day 14 may explain the late breakthrough infections, especially if the patient had a new exposure to the Monkeypox virus, cannot be confirmed based on our data but could be a hypothesis.

We did not find any new exposure for these two patients, but they were the only patients out of the 12 who possessed a pet animal.

The pet could theoretically be a reason for persistent exposure in these patients as domestic animals such as cats and dogs can be infected with Monkeypox virus.'

Bavarian Nordic Jynneos smallpox (Monkeypox) vaccine is authorized by the U.S. FDA, the EMA, and the U.K.

Additional monkeypox research is posted on this webpage.

Note: This study was translated and curated for mobile readership. And these researchers did not disclose any industry conflicts of interest.