Reports of Mpox disease following recent vaccination

By Suchandrima BhowmikDec 11 2022Reviewed by Benedette Cuffari, M.Sc.

Almost 21,000 cases of Mpox, formerly known as monkeypox, have been reported in Europe as of November 22, 2022. Despite this high rate of infections, there has been a reduction in the incidence of Mpox since August 2022 due to increasing immunity levels in at-risk populations through targeted vaccination campaigns, naturally-acquired infections, and behavioral changes.

Study: Severe mpox (formerly monkeypox) disease in five patients after recent vaccination with MVA-BN vaccine, Belgium, July to October 2022. Image Credit: Flabygasted / Shutterstock.com

Previous and current Mpox vaccination strategies

Due to a shortage of vaccines, many countries, including Belgium, introduced off-label vaccination regimens. As a result, Mpox vaccination was initially achieved with post-exposure preventive vaccination (PEPV) with the modified vaccinia Ankara (MVA-BN) in Belgium by the end of May 2022.

Primary preventive vaccination (PPV) with the administration of the first subcutaneous (SC) dose began at the primary Belgian sexually transmitted infection (STI) clinics at the end of July. However, the second dose was delayed and not administered within the recommended 28 days interval. Therefore, the vaccine was administered through the off-label intradermal (ID) route at one-fifth of the SC dose from September 2, 2022.

The vaccine supply was secured and given as two SC doses at a 28-day interval from the end of November. About 1,400 individuals received the first vaccine dose, 909 of whom received both doses by November 28, 2022.

Between July and August 2022, PPV vaccination was restricted to male and transgender sex workers, men who have sex with men (MSM) with at least one STI in the last year, laboratory personnel working with viral culture, and immunocompromised MSM. However, individuals who received the vaccine were not followed up.

A new study in Eurosurveillance aimed to analyze five Belgian patients with severe Mpox disease following PEPV or one- or two-dose off-label PPV.

About the study

The current study involves the collection of clinical, laboratory, behavioral, and demographic data from all participants.

Mpox diagnosis was confirmed through a quantitative polymerase chain reaction (qPCR) assay between one and 16 days following the onset of symptoms. Anal swabs were also collected from all participants.

Whole genome sequencing, phylogenetic analysis, and single nucleotide variant (SNV) analysis were also performed using the viral DNA isolated from the participants.

Vaccinated individuals experience severe Mpox symptoms

All study participants were cis MSM with a median age of 38 years, two of whom were HIV positive. All participants received one full dose SC of the MVA-BN vaccine, one as PEPV and four as PPV. In addition, two study participants were given a second preventive vaccination dose ID after 29 days of the first dose.

The time from the first and second dose to the onset of symptoms was four to 35 days and one to two days, respectively. Additionally, the exposure was between two days before and 32 days post-vaccination.

Localized anogenital symptoms were observed in all five participants. Three participants who received a single vaccine dose reported fever and other systemic symptoms, while two participants who received both vaccine doses did not report fever.

All patients experienced severe symptoms. Moreover, four individuals developed proctitis, one of whom also developed large, partly necrotic facial ulcerations. The fifth patient developed penile edema with bacterial superinfection.

Notably, symptoms in the participants who received a second dose ID were less severe than others.

Viral culture detected the presence of replication-competent Mpox virus (MPXV) in swabs from four participants. The viral genomes belonged to existing and different MPXV Clade IIb lineages. No common mutation pattern was observed among the four viral genomes.

Conclusions

The risk of infection and developing severe symptoms of Mpox remains, even after vaccination. Therefore, healthcare workers and those at high risk for Mpox infection must be made aware of the possibility of infection following vaccination and its potential symptoms. These findings indicate that a combination of vaccination with preventive measures is needed to provide better protection against Mpox infection.

Limitations

The sample size of the study was small. A second limitation was that asymptomatic and mild cases might have gone undiagnosed.