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 Trump administration has declined to release critical data to outside public health experts that would enable them to devise strategies against the virus that has killed 223,000 Americans and counting.

Federal agencies have told us that since March they have been compiling basic data for each county and city on Covid-19 cases, hospitalizations and deaths, the timing of social distancing mandates, testing, and other factors. This information can provide insights into how combinations of public health mandates — masks, social distancing and school closures, for instance — can keep the virus spread in check.