Recovered COVID patients show -0.23 SD global cognition deficit. Persistent symptoms cause -0.42 SD deficit. Early variants like original and B.1.1.7 produce larger deficits than Omicron. Hospitalized patients lose -0.35 SD from ICU admission. Memory, reasoning, and executive function drop -0.33 to -0.20 SD in persistent cases. Propensity-score matching confirms regression results. Two vaccine doses link to slightly lower cognition (b=0.057). Infection equates to about 3.5 IQ point drop. Vaccines equate to 0.8 IQ point drop. Self-selection may cause reverse causation where low IQ leads to infection. Vaccine uptake correlates with higher pre-existing intelligence. More vaccine doses show smaller IQ reductions, implying protection against infection effects. COVID damages brain via vascular clots and micro-clots. Direct brain infection occurs in minority cases. First exposure to COVID or vaccine may lower IQ most. Effects vary by individual susceptibility. Paper uses 112,964 completers from 141,583 starters. No adverse events reported.