Antiviral immunity following smallpox virus infection: a case-control study

Area of Science:

• Immunology
• Virology
• Epidemiology

Background:

• Smallpox (variola virus) caused high mortality, with survivors believed to have lifelong immunity.
• Previous studies quantified antibodies but lacked methods to assess T-cell memory after infection.
• Understanding immunity post-infection is crucial given smallpox eradication.

Purpose of the Study:

• To compare the duration and magnitude of antiviral T-cell and antibody responses in smallpox survivors versus vaccinated individuals.
• To determine if severe disease is a prerequisite for long-term immunity.

Main Methods:

• A case-control study involving 24 smallpox survivors and 60 smallpox-vaccinated controls.
• Measurement of antiviral CD4(+) and CD8(+) T-cell responses.
• Quantification of neutralizing antibody levels.

Main Results:

• Smallpox survivors exhibited slow-declining antiviral T-cell responses, similar to vaccinated individuals.
• Antiviral antibody responses in survivors remained stable for decades post-infection.
• Immunity duration after smallpox infection closely mirrored that after smallpox vaccination.

Conclusions:

• Sustainable long-term immunity can develop without experiencing severe disease.
• Smallpox vaccination induces immunity comparable in magnitude to natural variola virus infection.
• This immunological similarity likely contributed to the successful eradication of smallpox.