( CNN ) -- So you got a flu vaccine this season , and you 've been reading about the flu epidemic . You might be wondering : Will the vaccine keep me healthy ? The answer : The vaccine is n't a guarantee that you 'll be flu-free . In fact , it 's about 62 % effective , said the director of the Centers for Disease Control and Prevention , Dr. Thomas Frieden , on Friday . It can prevent the flu , and it can be beneficial even if you do get sick , said Dr. Bill Schaffner , chairman of the preventive medicine department at Vanderbilt University 's School of Medicine . `` It 's the best vaccine we have , but there are cases of influenza that occur despite immunization , '' Schaffner said on `` CNN Newsroom '' Thursday morning . The effectiveness of the vaccine depends , in part , on how well it matches the strains of viruses that actually end up prevailing during the flu season . So far , according to the CDC , this year 's North American vaccine matches well with the most predominant type of flu spreading in the United States , but is less well matched to the No . 2 type of virus . This year 's North American vaccine is made from three viruses : two types of influenza A virus ( H3N2 and H1N1 ) and an influenza B virus . As of January 5 , the CDC said Friday , the predominant virus in the United States was an influenza A ( H3N2 ) virus that matched well with the H3N2 virus represented in the vaccine . Of the H3N2 viruses tested at that point , 99.4 % matched the type that the vaccine protects against . The match for influenza B viruses , the second-most common this season , was n't as good . Of the influenza B viruses tested between October 1 and January 5 , 66.7 % were the type represented in the vaccine . The match for H1N1 , much rarer this season , was 100 % , the CDC said . Of the viruses collected and tested in the United States in early January , 20.2 % were influenza B and the rest were influenza A -- the vast majority of which appeared to be of the H3 variety , according to the CDC . The vaccine generally works better `` in young , healthy people than it does in older persons , '' Schaffner said . The CDC concurs : Even when vaccinated , some older people and people with certain chronic illnesses might not develop the same high levels of immunity as healthy , young adults , the CDC says on its website . What to do if you have the flu . But even if it does n't prevent illness in a particular person , the vaccine still can mitigate some of the symptoms . `` ( Flu vaccines ) are often of benefit because they can prevent some of the complications . It makes a more serious infection somewhat milder , '' Schaffner said . Keep in mind that the vaccine does n't work right away . `` It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against the flu , '' the CDC 's website says . Opinion : In the future , get vaccinated earlier . It 's not too late to get a flu shot , Schaffner said . `` Influenza is going to be with us into February and even beyond . If you have n't been vaccinated , please , take advantage of the benefits of influenza vaccine , '' he said . `` Run , do not walk -- get the vaccine . Protect yourself and everyone around you . '' National Institutes of Health : It 's an epidemic . If you did get the vaccine but still came down with the flu , you might wonder if the vaccine caused the illness . It did not , Schaffner said . `` You can get a bit of a sore arm if you get the injection . If you get the nasal spray variety , you can have a sore throat for a day and a runny nose . But you ca n't get flu from the flu vaccine , '' he said . Dr. Sanjay Gupta , CNN chief medical correspondent , endorsed getting a flu vaccine and frequently washing your hands . `` With soap and water , wash your hands for two 'Happy Birthday ' songs , '' he advised in an interview on CNN 's `` Anderson Cooper 360Ëš . '' If you have the flu , how are you treating it ? Send photos of your flu survival kits . CNN 's Carol Costello and Jason Hanna contributed to this report .
NEW : Vaccine is about 90 % effective , CDC director says . But the flu vaccine is n't a guarantee that you will be healthy . The most common flu infection this year is a match with the vaccine . But even if it does n't stop illness , it can stop some disease , Dr. Bill Schaffner says .