WASHINGTON—The number of Americans seeking unemployment aid fell slightly last week to 787,000, a historically high number that points to a weak job market held back by the viral pandemic. Thursday’s figure from the Labor Department, a slight decline from the previous week, shows that even with the pandemic recession in its 10th month, many businesses are still laying off workers. Before the recession, weekly jobless claims typically numbered around 225,000. The renewed surge in virus cases has caused millions of consumers to avoid eating out, shopping, and traveling. And states have imposed new restrictions on restaurants, bars, and other businesses. Economists at TD Securities estimate that more than half of states are now restricting gatherings to 10 people or fewer, up from roughly a quarter in September. Those restrictions are forcing many companies, having run through much of their cash reserves, to cut more jobs. “Unemployment remains extremely high, although …