A team of China-based scientists has recently estimated and compared the levels of anti-mpox and anti-vaccinia antibodies in gay men and the general population. The study is currently available on the medRxiv* preprint server.
Study: Unexpectedly higher levels of naturally occurring anti-Orthopoxvirus neutralizing antibodies are observed among gay men than general adult population. Image Credit: Dotted Yeti/Shutterstock
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Background
Mpox is a double-stranded DNA virus belonging to the Orthopoxvirus genus. The virus was initially endemic to Central and West Africa. However, multiple outbreaks have recently been detected in many non-endemic countries worldwide.
Most recent cases have particularly been detected in men who have sex with men (MSM). Unlike previous outbreaks, recent outbreaks exhibit some distinct features, including the faster spread of infection between humans and symptom similarities with other sexually-transmitted infections. These features suggest that special behavioral characteristics might make the virus spread more easily in this particular population.
Smallpox is a life-threatening infection caused by the variola virus, which also belongs to the same Orthopoxvirus genus. Vaccines developed against smallpox are, thus, expected to provide cross-protection against mpox infection.
Because of the complete eradication of smallpox infection in 1980, routine vaccination was terminated worldwide. Thus, a waning anti-smallpox immunity could serve as a fundamental cause of recent mpox outbreaks.
Although smallpox vaccine-induced antibodies are known to cross-protect against all Orthopoxviruses, recent evidence has indicated that anti-mpox neutralizing antibodies can be detected in people without any previous viral exposure or vaccination. This indicates that smallpox vaccination is not the only source of anti-Orthopoxvirus immunity.
In the current study, scientists have estimated and compared the blood levels of anti-mpox and anti-vaccinia antibodies in MSM and the general population residing in China. They have also compared the antibody responses in people born before and after 1981. In China, the smallpox vaccination ended in 1981.
Vaccinia is a poxvirus belonging to the Orthopoxvirus genus. The virus is used to produce vaccines against smallpox.
Study design
A total of 326 MSM and 295 general adults from China participated in the study. People with chronic diseases or active infections were excluded from the study.
Peripheral blood samples were collected from the participants to measure the levels of binding and neutralizing antibodies targeting specific proteins of the mpox virus and vaccinia virus.
Binding antibody response
The binding antibody response measured by ELISA revealed that the levels of anti-vaccinia antibodies are significantly higher among general adults born before 1981 compared to those born after 1981. However, no significant difference in antibody response was observed between MSM and male participants of the general population.
Regarding binding antibodies against mpox virus proteins, a relatively higher response was observed among general adults born before 1981. Considering participants born after 1981, a significantly higher anti-mpox antibody response was observed in the general population than in MSM.
Neutralizing antibody response
The scientists measured the levels of anti-vaccinia neutralizing antibodies with the speculation that the antibodies may provide a cross-reactive neutralizing response against the mpox virus.
The findings revealed that the anti-vaccinia neutralizing response is significantly higher in general adults born before 1981 compared to those born after 1981. Interestingly, the study found that MSM participants born after 1981 have significantly higher anti-vaccinia neutralizing antibody responses compared to their age-matched counterparts in the general population.
The scientists speculated that the anti-mpox immunity observed among study participants might arise from previous exposure to Orthopoxvirus. For confirmation, they determined the association between anti-mpox and anti-vaccinia antibody responses.
The analysis identified a positive correlation between anti-mpox and anti-vaccinia binding antibody responses in general adults born before 1981. However, no such correlation was detected in MSM and general adults born after 1981.
Overall, these observations indicate that the anti-Orthopox immunity observed among study participants born after 1981 might not be associated with previous exposure to Orthopoxvirus.
Study significance
The study identifies well-detected levels of anti-mpox and anti-vaccinia antibody responses in the general population and in MSM. Moreover, the study reveals a higher anti-vaccinia neutralizing response in MSM who did not receive smallpox vaccination.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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