HIV patients lose immunity to smallpox even though they were vaccinated against the disease as children and have had much of their immune system restored with anti-retroviral therapy, says a new study.

Antiretroviral therapy (ART) is the use of HIV medicines to treat HIV infection. It helps people with HIV live longer, healthier lives and reduces the risk of HIV transmission. The study, published in the Journal of Infectious Diseases on HIV-associated immune amnesia could explain why people living with HIV still tend to have shorter lives on average than their HIV-negative counterparts despite being on antiretroviral therapy. The study follows other research recently published in the journals Science and Science Immunology that found the immune systems of children who contracted measles similarly 'forgot' their immunity against other illnesses such as influenza.

According to the data from National AIDS Control Organisation, the total number of people living with HIV in India is estimated at 21.40 lakhs in 2017. India is estimated to have around 87.58 thousand new HIV infections in 2017, registering a decline by 85 per cent since the peak of 1995 and by 27 per cent between 2010-2017, the data revealed. Also, in 1970s, the World Health Organisation (WHO) declared that smallpox was completely eradicated from India. For the study, lead researcher Mark K. Slifka from Oregon Health and Science University in US, and his colleagues compared the T-cell and antibody responses of a total of 100 HIV-positive and HIV-negative women who were vaccinated against smallpox in their youth.

The research team chose smallpox because its last known US case was in 1949, meaning study participants haven't recently been exposed to its virus, which would have triggered new T-cell and antibody responses.They found the immune systems of HIV-positive women who were on antiretroviral therapy had a limited response when their blood was exposed to the vaccina virus, which is used in the smallpox vaccine. Normally, those vaccinated against smallpox have CD4 T cells that remember the virus and respond in large numbers when they're exposed again. Previous research has shown smallpox virus-specific CD4 T cells are maintained for up to 75 years after vaccination.

This finding happened despite the fact that antiretroviral therapy works by boosting CD4 T cell counts in HIV-positive patients. This indicates that while antiretroviral therapy may boost total T cell counts overall, it can't recover virus-specific T cells generated from prior childhood vaccinations. The research team plans to evaluate whether the same phenomenon occurs in HIV-infected men, and if people living with HIV also lose immune memory to other diseases. Researchers from SUNY Downstate, Georgetown University, Cornell University, University of Southern California and John Hopkins University, also contributed to this study.