The shared “pox” terminology between chickenpox and Mpox (formerly Monkeypox) often causes confusion about whether having one disease protects you from the other. Both viral illnesses cause a notable rash with blister-like lesions, which is the historical reason for the similar naming convention. However, the diseases are caused by two entirely different viruses from distinct families. Prior infection with one offers no reliable defense against the other.
Separating Viral Families: Chickenpox and Mpox
Chickenpox is caused by the Varicella-Zoster Virus (VZV), which belongs to the Herpesviridae family, making it a herpesvirus. This virus is a double-stranded DNA virus that is highly contagious and also causes shingles later in life after reactivation. The VZV infection is characterized by lesions that typically appear in different stages simultaneously across the body, often starting on the trunk.
Mpox is caused by the Monkeypox virus (MPXV), which is a member of the Orthopoxvirus genus within the Poxviridae family. This places the Mpox virus in the same genus as the variola virus that caused smallpox, as well as the vaccinia virus used in the smallpox vaccine. Despite the similar appearance of the skin lesions, the fundamental genetic structures of a herpesvirus and an orthopoxvirus are completely different. Mpox lesions tend to be firmer and evolve in a more synchronous manner across the affected area.
The Direct Answer: Cross-Immunity and Susceptibility
Having previously had chickenpox, or being vaccinated against it with the VZV vaccine, does not provide effective protection against Mpox infection. The human immune system develops highly specific antibodies and T-cells to combat the Varicella-Zoster Virus. These immune components are finely tuned to recognize the unique surface proteins, or antigens, of VZV.
Because the Mpox virus is genetically and structurally distinct from VZV, the immune response generated by a prior chickenpox infection does not recognize the Mpox virus antigens. VZV-specific antibodies are not a match for MPXV and cannot neutralize or clear the Mpox virus effectively. The two viruses can even co-circulate or co-infect a person at the same time, which further highlights the lack of cross-protection. Therefore, an individual who recovered from chickenpox remains fully susceptible to infection with the Mpox virus.
Clarifying Protection: The Role of the Smallpox Vaccine
Confusion about “pox immunity” often stems from the close relationship between Mpox and smallpox. Since Mpox is an Orthopoxvirus, it shares significant genetic and antigenic similarities with the vaccinia virus used in the smallpox vaccine. This close family relationship means that the smallpox vaccine can provide a significant degree of cross-protection against Mpox.
The vaccinia virus in the smallpox vaccine elicits an immune response that recognizes the shared antigens among all Orthopoxviruses, including MPXV. Studies have estimated that the older smallpox vaccine provides approximately 85% cross-protection against Mpox, and this immunity can last for decades. The success of the smallpox vaccine against Mpox is due to this shared genus classification.
This mechanism is entirely different from the VZV vaccine, which is only designed to protect against the herpesvirus that causes chickenpox and shingles. Protection against Mpox comes from a vaccine developed for a related Orthopoxvirus, not from the immunity gained from a prior infection with the unrelated VZV.