CHICAGO -- Because Catherine Murphy's 13-month-old son Jack has a compromised respiratory system, getting flu shots for her entire family is a no-brainer. But the flu vaccine may not be very effective this winter, according to U.S. health officials who worry this may lead to more serious illnesses and deaths.
"Even if we get a common cold it can land Jack in the ICU, so anything we can do to help protect and keep our house healthy and clean helps protect him as well," Murphy said.
It's a good idea, some doctors say, because it appears the current flu season is already here.
"We're getting into the flu season now, so we're getting more and more positive flu tests everyday both A and B, so flu season is here," said Dr. Payal Adhikari.
According to the Centers for Disease Control and Prevention, early data suggests the the 2014-2015 flu season could be severe because about half of the most common H3N2 flu viruses have mutated, meaning this season's vaccines don't quite match up and as a result may have a reduced ability to protect against those viruses.
Dr. Allison Bartlett, an assistant professor of pediatric infectious diseases at the University of Chicago, says that's not a reason to avoid vaccination.
"In the past when that has happened, although the vaccine hasn't been perfectly effective, it has helped. So people may still get the flu, but they'll get much less sick than they would have," said Dr. Bartlett.
Flu activity doesn't usually peak until January or February in the United States, and can last as late as May.
According to Walgreens, along with health departments for Chicago and Illinois, Illinois ranks seventh out of the top 10 states for flu activity based on weekly retail prescriptions for antiviral medications.
Also, so far this season, 20 people in the state have been admitted to hospitals for the flu, and three have died.
Flu vaccine effectiveness tends to vary from year to year. Last winter, flu vaccine was 50 to 55 percent effective overall, which experts consider relatively good.
The CDC issued an advisory to doctors about the situation Wednesday evening.
CDC officials said doctors should be on the look-out for patients who may be at higher risk for flu complications, including children younger than 2, adults 65 and older, and people with asthma, heart disease, weakened immune systems or certain other chronic conditions.
Such patients should be seen promptly, and perhaps treated immediately with antiviral medications, the CDC advised. If a patient is very sick or at high risk, a doctor shouldn't wait for a positive flu test result to prescribe the drugs - especially this year, CDC officials said.
The medicines are most effective if taken within two days of the inset of symptoms. They won't immediately cure the illness, but can lessen its severity and shorten suffering by about a day, Frieden said.
Among infectious diseases, flu is considered one of the nation's leading killers. On average, about 24,000 Americans die each flu season, according to the CDC.
Nearly 150 million doses of flu vaccine have been distributed for this winter's flu season.
Current flu vaccines are built to protect against three or four different kinds of flu virus, depending on the product. The ingredients are selected very early in the year, based on predictions of what strains will circulate the following winter.
One of the vaccine components chosen last February was a certain strain of the H3N2 virus. About a month later - after vaccine production was underway - health officials noted the appearance new and different strain of H3N2. "This is not something that's been around before," Frieden said.
Health officials said they weren't sure if the new strain would become a significant problem in the United States this winter until recently. Lab specimens from patients have shown that the most commonly seen flu bug so far is the new strain of H3N2. Specifically, about 48 percent of the H3N2 samples seen so far were well matched to what's in the vaccine, but 52 percent were not, the CDC said.
This news follows another problem recently identified by CDC officials, involving the nasal spray version of flu vaccine.
At a scientific meeting at the CDC in October, vaccine experts were told of preliminary results from three studies that found AstraZeneca's FluMist nasal spray had little or no effect in children against the swine flu strain that was the most common bug making people sick last winter.
Because this year's version of FluMist is the same formulation, experts said it's possible the spray vaccine won't work for swine flu this season, either.
However, CDC officials believe H3N2 will be the most common flu bug this winter.
The Associated Press contributed to this report.
Flu vaccine may not be effective for this year's strains, CDC says