As seen in other populations in many countries, a substantial
proportion of Thai MSM in Bangkok seroconverted to
A(H1N1)pdm09 during the 2009 pandemic in the absence of
A(H1N1)pdm09 vaccine and in the setting of limited availabil-
ity of seasonal influenza vaccine. Although HIV infection did
not appear to increase the probability of A(H1N1)pdm09 sero-
conversion, the majority of HIV-infected MSM in this study
were young and had relatively preserved immune function. It
remains unclear whether severely immunocompromised per-
sons infected with HIV are more susceptible to A(H1N1)
pdm09 influenza virus and to seasonal influenza viruses in ge-
neral. Given that persons infected with HIV are at risk for more
complicated illness once infected with influenza, these individ-
uals should continue to be prioritized for influenza vaccination
during seasonal influenza epidemics and pandemics.