IFNG and smallpox: As compared with healthy controls without vaccination against smallpox (Figure 1, unvaccinated, left group), the HIV-positive patients with two vaccinations against smallpox displayed significantly higher orthopoxvirus-specific IFN-γ ELISpot responses (p < 0.0001), and the IL-2 ELISpot responses tended to be higher (p = 0.08).