Trials studying the Covid-19 vaccine have included people with H.I.V., albeit in small numbers. The Pfizer trial included 120 people with H.I.V., and the Moderna trial included 176 people with H.I.V., according to Poz, a news site for people living with and those affected by H.I.V./AIDS. Although the numbers are too small to draw meaningful conclusions, no unusual safety concerns were reported for people with H.I.V. Because the Pfizer and Moderna vaccines do not contain weakened or inactivated virus, they are believed to be a safe option for people with H.I.V. and AIDS. Like other people with weakened immune systems, people with H.I.V. and AIDS who received the Pfizer or Moderna vaccines now are eligible for a third shot four weeks after the second dose. —Tara Parker-Pope