Monkeypox Outbreak: Asymptomatic Infection Could Be A Cause For Concern, New Study Says

Vaccination limited to the persons with known exposure to the monkeypox virus may not be an effective strategy for preventing infection, the study suggests.

Scientists have detected the monkeypox virus in anal samples taken from asymptomatic men who have sex with men (MSM). This means that asymptomatic infection may be a cause for concern in the monkeypox outbreak, according to a new study. 

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Scientists have detected the monkeypox virus in anal samples taken from asymptomatic men who have sex with men (MSM). This means that asymptomatic infection may be a cause for concern in the monkeypox outbreak, according to a new study. 

Vaccination limited to the persons with known exposure to the monkeypox virus may not be an effective strategy for preventing infection, the findings suggest. The study describing the results was recently published in the journal Annals of Internal Medicine. 

How The Study Was Conducted

Researchers from Bichat-Claude Bernard Hospital, Paris, France, collected anorectal samples as part of a sexually transmitted infection screening programme, and tested them for monkeypox virus. According to French guidelines, this type of screening is performed every three months among MSM with multiple sexual partners who are either taking HIV pre-exposure prophylaxis (PrEP) or living with HIV and receiving antiretroviral treatment. PrEP is a medicine people at risk for HIV take to prevent getting HIV from sex or injection drug use, and can stop HIV from taking hold and spreading throughout the body. So far, the US Food and Drug Administration (FDA) has approved two daily oral medications for PrEP, and a long-acting injectable form of PrEP.

The first case of monkeypox virus infection was identified in France on May 19, 2022. After this, screening was halted in patients who had lesions suspicious for monkeypox virus. The study authors report on asymptomatic MSM who tested negative for N gonorrhoea and C trachomatis on monkeypox virus anal swabs collected at the Infectious Disease Department and the Sexual Health Clinic of Bichat-Claude Bernard Hospital, from June 5 to July 11, 2022. 

The median age of the 213 participants whose anal swabs were collected was 38 years. 

A total of 213 asymptomatic persons were screened as part of the study. The persons were negative for Neisseria gonorrhoeae and Chlamydia trachomatis. 

Findings

Of these, 13 samples were PCR-positive for monkeypox virus. Later on, two of these persons developed symptoms for monkeypox. 

Of the 187 asymptomatic participants who tested negative for monkeypox virus, three presented to the authors' clinic more than three weeks after the initial monkeypox virus-negative anal swab with symptoms suggestive of monkeypox virus infection, and tested positive, the authors note. 

The study documents positive monkeypox virus PCR results from anal samples in asymptomatic MSM. However, it is not known whether this indicates viral shedding that can lead to transmission. 

The authors state that the practice of ring postexposure vaccination around symptomatic persons with probable or confirmed monkeypox may not be sufficient to contain the spread. Ring vaccination is a vaccine strategy in which the people who are most likely to be infected with a disease are vaccinated to inhibit the spread of the disease. 

The authors conclude that recent French recommendations have advised vaccination for all MSM with multiple partners. 

Scientists do not know yet whether or not asymptomatic infection will play a role in the transmission of monkeypox virus. However, the current worldwide monkeypox epidemic and the mode of human-to-human transmission may suggest that asymptomatic or preclinical spread can occur.