We are now halfway through the 2019-20 flu season and a new strain of influenza is picking up—increasing the odds that we may experience what infectious disease experts are calling a “double-barreled flu season.”

The Centers for Disease Control (CDC) reports that so far this season, there have been at least 15 million cases of the flu, 140,000 people have been hospitalized, and more than 8,000 have died from the virus, including more than 50 children. The majority of confirmed flu cases have been caused by a B strain of influenza.

“One of the strains that’s making a lot of kids sick right now is called Type B/Victoria. The match on this year’s flu vaccine, although it has B/Victoria in it, is not perfect,” says Dr. Pilar Bradshaw.

The CDC estimates that this year’s influenza vaccine may only protect against 58% of B/Victoria cases, and it’s been nearly 30 years since B strains have hit children this hard. What’s concerning doctors is another flu strain, known as A/H1N1, that’s overlapping B/Victoria. The good news, Dr. Bradshaw says, is that this year’s flu vaccine appears to be a good match for A/H1N1.

The most worrisome part of a double-barreled flu season is that you can get sick twice. Just because you caught a B strain flu does not mean that you are immune from the A strains, so a flu shot is still your best defense against influenza, says Dr. Bradshaw.

“The flu vaccine is not perfect, but it is your best protection against your kid being hospitalized or dying from influenza. Even if your child has already had influenza type B this year, still get the vaccine if they haven’t been vaccinated yet because influenza A will hit.”

A double-barreled season also means we’re more likely to see a prolonged flu season, so individuals and families are encouraged to get vaccinated as soon as possible. It takes about 10-14 days after receiving the vaccine for a person’s antibody levels to respond. If you have an infant 6 months or older who is getting their first flu shot this year, he or she will need a booster shot 30 days after their initial vaccination.

Final estimates on the effectiveness of this year’s flu vaccine cannot be made until the flu season is over and scientists can analyze the data.