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Of the 63 American children killed by the flu virus so far this season,Watch Workplace Picnic Goal Online just 13 had been vaccinated.

Top government doctors — including the Surgeon General, Secretary of Health and Human Services, and acting head of the Centers of Disease Control and Prevention (CDC) — found this lack of vaccination so alarming that late Thursday afternoon they offered a joint briefing on the matter.

"Getting the flu shot is the same kind of sensible precaution as buckling your seatbelt," said Health Secretary Alex Azar.

Before today, the effectiveness of this season's vaccine wasn't officially known, but now the CDC says the vaccine is 36 percent effective, overall.

"Imagine if you could cut your chances of being in a car crash by 36 percent," said Azar.

The top heads of the U.S. health departments didn't openly state concerns that some Americans might not be vaccinating themselves or their children due to an unfounded wariness about the flu vaccine. They did, however, underscore that the flu shot should not be feared.

"The vaccination is safe. Let me say that again — the flu vaccine is safe," said U.S. Surgeon General Jerome Adams.

This #flu season, make sure love is the only thing in the air. Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick. https://t.co/8Sc7GaIUV6 #ValentinesDay pic.twitter.com/7FvjfbwEDQ

— CDC Flu (@CDCFlu) February 14, 2018

To emphasize this point, both Adams and Secretary Azar said their own children had been vaccinated against the flu. Azar also noted that President Trump and all the medical experts on the stage had been vaccinated.

This flu season has been particularly severe. For the last week of confirmed data (Jan. 28 through Feb. 3), the CDC reported the highest rate of hospitalization for flu ever recorded since the current system was implemented in 2005.

"I know it’s been a scary flu season," said acting CDC Director Anne Schuchat, who gave the statistic that three of four children killed by flu had not been vaccinated.

Schuchat said that the levels of people reporting influenza-like Illness, or ILI, are "around" what the U.S. experienced during the H1N1 pandemic in 2009. However, "it doesn’t mean we’re having a pandemic right now," she clarified.

A flu pandemic, according to the CDC, involves an outbreak of a new infectious virus. This year, all the strains are known, even expected. But this season's dominant strain, known as H3N2 or the "Hong Kong" flu, is especially virulent because it tends to mutate more than other strains, rendering our vaccines less effective.

Although the flu vaccine in the U.S. is 36% effective overall, Schuchat said it's been only 25 percent effective against H3N2, but over 60 percent effective against H1N1.

"We do continue to recommend getting the vaccine even this late in the season," Schuchat said.

Although the vaccine may not stop the flu, it will bolster the body's immune response against the virus, tempering its effects. This can help avoid hospitalization for severe symptoms, or at worst, death.

"This flu season continues to be extremely challenging and intense," said Schuchat. "All indication is that flu activity remains high and is likely to continue for several more weeks."

It's not too late to get your shot.