LONDON—Oil rose by more than $1 a barrel to above $71 on Monday as hopes that the Omicron coronavirus variant may cause mostly mild symptoms boosted riskier assets and as the prospect of an imminent rise in Iranian oil exports looked less likely. Helping ease Omicron concerns, reports in South Africa said cases there only had mild symptoms and the top U.S. infectious disease official told CNN “it does not look like there’s a great degree of severity” so far. Brent crude gained $1.77, or 2.5 percent, to $71.65 by 0920 GMT while U.S. West Texas Intermediate crude advanced $1.69, or 2.6 percent, to $67.95. Both benchmarks declined for a sixth week in a row last week. “If Omicron is proven over the coming days (or weeks) to be less aggressive, even if it is more contagious, then we can say 100 percent last week’s lows were the bargain of …