Early voting has already generated long, long lines in many states, and with the November election just 11 days away, many states and cities have imposed safety measures to protect voters and poll workers from exposure to the coronavirus.But polling places still have the potential to become “mass gathering events,” the Centers for Disease Control and Prevention warned in an advisory released on Friday, adding that measures to prevent the spread of Covid-19 could be improved.The C.D.C. based its latest advice on a survey from the experiences of 522 poll workers in Delaware’s statewide primary in September.Guidelines issued by the agency in June recommended various ways to minimize crowds at polling locations, including absentee voting and extended voting hours.To cut down on disease transmission, the C.D.C. also recommended putting up physical barriers between voting machines; spacing the machines apart from one another; indicating 6-foot distances with signs or floor markings for those waiting in line to vote; designating separate entrances and exits; the use of protective gear — masks, face shields, gloves and gowns — for poll workers assisting sick voters; and allowing curbside voting for people who are ill.“Ensuring that ill voters can vote while maintaining poll worker and voter safety will be essential to minimizing transmission without restricting voting rights,” the report said.But in Alabama, where curbside voting had been allowed, the state’s attorney general ordered that it be stopped, and on Wednesday, the U.S. Supreme Court upheld the ban.The new survey of Delaware poll workers did not provide information about whether any cases of Covid were linked to the voting centers. The questions involved only the workers’ observations about the conditions and practices at 99 of the state’s polling places.The Delaware survey found that most workers and voters wore masks, but did not always use them properly to cover both the mouth and nose. Voters were less careful than poll workers. About 73 percent of the respondents said they very rarely or never saw other poll workers wearing masks the wrong way. But only 54 percent of the workers surveyed said that they rarely or never saw sloppy mask use by voters.Noting that “a substantial proportion” of the poll workers saw incorrect mask use by voters, the report said, “further messaging on proper mask use, including at polling locations, might be needed to strengthen the effectiveness of masks during upcoming elections.”The C.D.C. suggested that providing masks for voters “might support adoption of personal prevention practices.”Poll workers were also more likely than voters to use hand sanitizer.Nineteen of the 522 workers in the survey had contact with a voter who was ill, with or without a known Covid diagnosis, the report said. Fifteen of the 19 said they wore masks during that contact, but none wore the other protective gear recommended by the C.D.C. for such encounters: face shield, gown, gloves. The survey suggested that the workers had “limited training” in use of the gear.Poll workers in general face multiple risks: Many are older, with health problems that make them especially vulnerable to severe illness if they contract Covid. And they come into close contact with many people on election days, often closer than the 6-foot “social distance” recommended to minimize transmission of the virus.Continuing efforts to recruit younger poll workers might reduce the proportion of workers at risk for severe cases of Covid, the report said.In the meantime, the C.D.C. offered up a list of ways to help minimize the risk for voters: go at off-peak times, like midmorning; monitor the voter line from your car and join when the line is short; fill out any needed registration forms ahead of time and review a sample ballot at home to cut down on time spent at the polling location; and take your own black ink pen, or stylus to use on touch-screen voting machines.