(CNN) Don't let your guard down: The US flu season is expected to continue for several more weeks, with activity across the nation now elevated, the US Centers for Disease Control and Prevention reported Thursday. A flu shot is still recommended for those who have neglected to get one, but the CDC estimated this year's vaccine's overall effectiveness in preventing an infection at just 47%.

The shot's success varies based on your age, the CDC noted. Among children up to 17, its overall effectiveness against flu was 61%, while just 24% of adults 50 and older who received the shot gained protection against infection.

Dr. William Schaffner, medical director of the nonprofit National Foundation for Infectious Diseases, said that those who get flu after receiving vaccine are less likely to require hospitalization and are less likely to die of the illness.

"The vaccine is not perfect," Schaffner said. "But give the vaccine credit for softening the blow."

The virus' severity this season compared with last has been low, with a smaller percentage of doctor's office visits, lower rates of hospitalization and fewer deaths through February 2, the CDC reports. The official start of the season was September 30; activity remained low during October and November, increased in late December and then remained elevated through early February.

Twenty-eight children have died of flu-related complications this season as of February 2, the CDC noted.

"Fingers crossed that we're now heading toward the bottom part of the season," said Richard Webby, a flu scientist and adviser to the World Health Organization on recommendations for the composition of flu vaccines. "Overall, it's been a relatively mild season, and compared to last year, it's a bit of a welcome reprieve."

The reason for that is that milder H1N1 strains of the influenza virus have dominated in most of the country, with H3N2, a strain that causes more severe illness that ran rampant last winter, predominating in southeastern areas.

In recent weeks, though, the proportion of illness due to H3N2 has grown in several regions.

Last winter was the deadliest US flu season in more than four decades. An estimated 80,000 Americans, including 180 children, died of flu and its complications, the CDC reported. Additionally, the nation experienced an estimated 900,000 hospitalizations, a record, during the last season.

Overall, the effectiveness of the seasonal flu vaccine for last season was estimated to be 40%. This means the vaccine reduced a person's risk of having to seek medical care by 40%, the CDC found. Yet, among children, the shot was estimated to be 59% effective.

Despite the fact that the strains circulating this winter are aligned with the viruses used to make the vaccine, the manufacturing process tends to cause slight changes that create a mismatch, Webby explained. This season's flu shot is "clearly not where we want it to be, but it has been superior overall than the past few seasons," he said.

The CDC also recommends antiviral medication for people "with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at high risk for influenza complications."

In October, the US Food and Drug Administration approved a new antiviral, baloxavir marboxil or Xofluza, a single-dose oral prescription drug . The pill is intended for patients 12 or older who have had symptoms for no more than 48 hours.

The antiviral is the first flu treatment approved by the FDA in nearly 20 years. During past seasons, Tamiflu has been the antiviral medication prescribed for many people.

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When patients with the flu are treated within 48 hours of becoming sick, antiviral drugs can reduce symptoms and duration of illness, according to the FDA. There are side effects for both drugs, including diarrhea, bronchitis, headache and nausea for Xofluza and nausea, vomiting, diarrhea and headache for Tamiflu.