At least three more states -- Montana, South Dakota and Arizona -- are now reporting widespread flu, bringing the total to 44 states. And the CDC says the percentage of people going to the hospital for treatment of flu symptoms has doubled in the past month.
The emergency in Boston was declared after confirmed cases of flu reached 700. There were just 70 at this time last year. Across the state, 18 patients have died.
"In the last two weeks alone we've doubled our number," said Dr. Barbara Ferrer, the executive director of the Boston Public Health Commission. "So, if we continue at this rate to see new cases, we'll have an explosion of flu in the city of Boston. We really need to get ahead of it at this point in time."
Flu surge leads to Boston public health emergency
Centers for Disease Control: High level of flu reports in 29 states
To do that, officials are urging vaccination for everyone six months and older. Clinics will be giving free shots this weekend.
Lehigh Valley Hospital in Pennsylvania is getting as many as 100 patients a day with flu-like symptoms. A tent has been set up to handle the less serious cases.
"We need a full functioning active emergency dept for the community," said nurse Terry Burger, who is in charge of infection control. "And this just enables us to see the patients that are not as sick. So mild illness, mild injuries...see them quickly, and then discharge them."
About 60 miles south in Chadds Ford, the entire Coan family got the vaccine, but eight-year-old Alex came down with the flu anyway.
"You cough a lot," he said, "kind of sneeze a little, lay in bed all day."
His mother Christine said: "As a mom, I was very disappointed that he got the flu, because I had to fight him tooth and nail to get the flu shot."
In recent years, the vaccine has been about 60 to 70 percent effective at preventing the flu. Recently, scientists discovered this year's vaccine is not protecting against a specific strain.
Dr. William Shaffner, who is on the panel that decides what goes in the vaccine, said: "There is an influenza B strain that's out there, an additional strain that's causing about 10 percent of the mischief. And that's not in the vaccine and that accounts for some of the influenza that's out there."
The CDC told CBS News this year's vaccine is still very well-matched to the strains that are out there. Even when the flu vaccine does not prevent the flu, it can still stop complications including pneumonia and even death.
As for how does this outbreak compares historically -- a lot of people don't realize that the flu varies in intensity from year to year. In some years it's mild; it could be moderate; or it gets to be severe. The CDC told CBS News that this is a moderate to severe season, but it's well within what's historically a range of normal.