FRIDAY, Jan. 15, 2016 (HealthDay News) -- The mild flu season continues to be that way, U.S. health officials said Friday, but they expect activity to pick up in coming weeks.
So anyone who hasn't gotten a flu shot should get one now.
"Flu activity continues to increase, but slowly," said Lynnette Brammer, an epidemiologist in the influenza division at the U.S. Centers for Disease Control and Prevention.
Flu infections, which had been reported in Southeastern states in recent weeks, are starting to increase in the West and Northwest, Brammer said. "But the increase is still very small," she added.
This year's slow start to the flu season isn't out of the ordinary -- other flu seasons have had the same pattern, Brammer said.
"The last three years' flu season was earlier than normal, so this one feels late," she said. "But this is really not unusual for flu season."
In past similar flu seasons, the peak didn't come until February, and in one case the flu peaked in March, she said.
Milder weather may be one factor delaying this year's flu, Brammer said. But it's only one factor of many that affect how flu spreads. Other factors include how many people are immune because they've been vaccinated and the low number of people with flu who could infect others.
In a typical flu season, flu complications -- including pneumonia -- send more than 200,000 Americans to the hospital. Death rates linked to flu vary annually, but have gone as high as 49,000 deaths in a year, the CDC says.
Virtually everyone older than 6 months of age is advised to get a flu shot. The exceptions are people with life-threatening allergies to the flu vaccine or any ingredient in the vaccine, according to the CDC.
Pregnant women are at high risk and should get vaccinated. Women with newborns also need to get their flu shot to help protect their infants, who can't be vaccinated until they are at least 6 months old. Also at risk are seniors and people with chronic health problems, such as lung and heart disease, the CDC says.
How effective the vaccine is in preventing the flu depends on how good a match it is to the strains of flu virus circulating that year. Most years, the vaccine is between 40 percent and 60 percent effective, according to the CDC.
Last year, the vaccine offered little protection against the most common flu strain that circulated, an H3N2 virus, Brammer said.
That happened because the virus that experts had predicted to be predominant wasn't, and the new H3N2 virus was not included in the vaccine, she explained.
This mismatch caused a severe flu season, especially for the very old and very young, and led to a record number of hospitalizations for flu among the elderly, according to the CDC.
This year's vaccine contains the new H3N2 strain, but it's too early to tell which strains will dominate, Brammer said.
Plenty of vaccine is still available, but Brammer said supplies may be dwindling in some regions. In some areas of the country you may need to make a couple of calls to find the vaccine, she added.
"It's not too late to get vaccinated," she said. "We are expecting a lot more flu coming down the road. So this is still a great time to go get vaccinated."
For more on flu, visit the U.S. Centers for Disease Control and Prevention.