This flu season, many of us have known people who got a flu shot and still got sick. Does that mean this year's vaccine was bad?

The U.S. Centers for Disease Control and Prevention doesn't think so.

It announced Thursday that the shots are 48 percent effective against all the strains of flu that have been circulating.  That's good, the agency said, because it means the shots are reducing by nearly half an individual's risk of getting sick enough with the flu to need to go to the doctor.

The numbers are a little lower for the influenza A variety that has dominated this year's flu season.  The vaccine is just 43 percent effective against that strain, the preliminary report said.  A more detailed report will be released in several months.

Individuals, though, might wonder why they should bother getting a shot that only works less than half the time.

"Whether you think that overall close to 50 percent protection is good or not good depends on whether you're a glass-half-full or a glass-half-empty kind of person," said Bennett Lorber, a professor of microbiology and immunology at the Lewis Katz School of Medicine at Temple University.

He and Neil Fishman, an infectious-disease expert and associate chief medical officer at the University of Pennsylvania Health System, said the flu vaccine is flawed, but valuable.  It may help to think of it as a small sacrifice we all can make for our community, even if some of us still get sick.

"I'm not saying this is a wonderful vaccine," Fishman said. "I think there are definitely opportunities for improvement. ...  In 2017, it is the best intervention we have to prevent influenza and certainly to prevent severe influenza and severe complications of influenza."

Fishman said the new report focuses only on patients seen in outpatient offices.  The later one will look at hospitalizations and deaths, consequences of the flu he considers much more important.

Both Fishman and Lorber pointed out that people who get the shots likely have less serious symptoms of flu if they still get sick.  Plus, we should be getting the shots not just to protect ourselves but to protect coworkers and family members who are more vulnerable to serious complications.

"Suppose you got the flu and you have a household member with life-threatening lung disease," Lorber said. "You might as well put a gun to their head and pull the trigger."

And, he pointed out, most people would want to significantly reduce their odds of getting really sick even if the odds weren't perfect. "Influenza is a serious illness," he said.  "People die from this."

Unlike, say, measles, flu presents special challenges for vaccines.  There must be a new vaccine each year based on strains of flu that are expected to circulate.  Those change every year and predictions are not perfect.  This year's flu vaccine is a good match for the strains in circulation, but the type of influenza A now making the rounds tends to morph a little during a season.

"What people are working toward and what I hope we will eventually have is a universal vaccine that works for every influenza virus," Lorber said. "I think that will happen."

Influenza-vaccine effectiveness this year is comparable to last year.  During the 2014-15 flu season, it was only 23 percent. Back in 2004-05, effectiveness was only 10 percent.  The 2010-11 season was a good one for the shots, with effectiveness at 60 percent.

Fishman and Lorber agreed that there have been a lot of sick people this year, but, generally, the symptoms have been milder.  "We have had very few, if any, people hospitalized for influenza," Fishman said.  It's too early to know whether that's because of the vaccine or because the disease itself was milder this year.

Earlier in the season, there were several respiratory viruses, including flu, making people sick.  Flu is dominating now, but RSV and human metapneumovirus are still in the mix.  They have similar respiratory symptoms to flu, and both can make some people quite sick. The flu vaccine does not prevent them.

According to the CDC, much of the country, including New Jersey and Pennsylvania, is currently experiencing high levels of influenza-like illness.

Fishman thinks the local flu season is reaching its peak.  Influenza B strains are rising, usually a sign that influenza A is on the way out.  This year's shot is much more effective against B — 73 percent — than A.

Public-health authorities, by the way, are saying there are weeks left in this year's flu season, and you should still get the shot if you haven't yet.