CLOSE Flu changes each year, but the need for a vaccine doesn't. Wochit 
 
 A University of Tennessee senior nursing student, Jordan Gause, administers a free flu shot Sept.16, 2017, in Knoxville, Tenn. (Photo: Andrew Capps, Knoxville (Tenn.) News Sentinel) 
 
 Outbreaks of influenza are getting an early start this year in part because of cold weather gripping much of the USA and low efficacy associated with this year's flu vaccine. 
 
 It's still too early to say whether this winter will be a bad season for the flu, but epidemiologists in 36 states already have reported widespread influenza activity to the federal Centers for Disease Control and Prevention in data released Friday. Twenty-one of those states show a high number of cases. 
 
 "It's just one of those years where the CDC is seeing that this strain of flu is only somewhat covered by the vaccine that was given this year," said Jennifer Radtke, manager for infection prevention at the University of Tennessee Medical Center in Knoxville. "They're seeing that it's anywhere from 10% to 33% effective, so any time there’s a mismatch between the vaccine and the circulating strain of the flu, you’re going to see more cases." 
 
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 Peak flu activity in the U.S. usually occurs around February. 
 
 Vaccine effectiveness varies from year to year though recent studies show that a flu shot typically reduces the risk of illness by 40% to 60% among the overall population when the circulating virus is matched closely to the vaccine virus, according to the CDC. 
 
 “It's not uncommon to see (flu) this time of year. But we've had cold Decembers before and not had flu.” Jennifer Radtke, University of Tennessee Medical Center 
 
 Because only a certain percentage of people with flu symptoms go to hospitals and get tested, it can be challenging to track the actual number of people affected, Radtke said. False negative results for flu tests are also common, so it’s likely the number of people with the flu is much higher. 
 
 From the start of the flu season, which begins in October and lasts until May, Arizona has reported a nearly ninefold increase in the number of cases compared with the same period last year, according to the state Department of Health Services. 
 
 "It's not uncommon to see (flu) this time of year," said Radtke in Knoxville. "But we've had cold Decembers before and not had flu." 
 
 Flu symptoms include fever, body aches, chills, fatigue, cough and a sore throat. The illness typically passes within a few days but can be especially dangerous to the very young, the very old, pregnant women and those with respiratory problems. 
 
 Influenza can develop into pneumonia, an infection that causes the lungs' air sacs to become inflamed and fill with fluid. 
 
 Deaths already have occurred in some states this flu season. Among them: 
 
 • In Arizona, the state is reporting one death of a child in its latest tally; however, an otherwise healthy 20-year-old mother of two in Phoenix died Nov. 28, one day after being diagnosed, CBS News reported. 
 
 • In California, at least 10 people younger than 65 have died, according to the San Francisco Chronicle. An 11th death occurred Thursday. The state does not track flu-related deaths among those 65 and older. 
 
 • In Delaware, a 47-year-old man with underlying health problems and an 83-year-old woman have died, state health officials said. 
 
 • In North Carolina, 12 people, including a child, have died. 
 
 • In South Carolina, seven have died. All were age 65 or older. 
 
 Getting a flu shot now is still one way to combat the virus even though it can't promise total immunity, health officials say. 
 
 More insurers fully cover the cost, and pharmacists in all states now can administer the vaccinations, according to the American Pharmacists Association trade group. 
 
 "People are able to come in to the pharmacy — especially a 24-hour pharmacy like this one where you can come in at literally any time — and be in and out usually within 15 minutes," said Jason Lind, a Walgreens pharmacist in St. Cloud, Minn. 
 
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 Also to keep the germs at bay, wash or sanitize your hands frequently, especially if you're touching shared surfaces such as shopping carts in public places; clean faucet and toilet handles frequently at home to reduce transmission of the virus within your family; cover your mouth when coughing; stay home when you're sick; stay away from sick people; and avoid touching your face. 
 
 It also pays to stay well rested and hydrated so if you do come in contact with a flu virus, your body is prepared to fight it off. 
 
 If you're already feeling ill, get to a doctor as quickly as possible. 
 
 ► Oct. 24: U.S. vaccine panel to discuss waning effectiveness, new shots 
 
 ► Oct. 17: 7 ways to meet the costs of cold and flu season 
 
 Antiviral prescription drugs such as Tamiflu can lessen the severity of influenza for people who have had flu symptoms for two days or fewer and prevent complications such as pneumonia. But they also can have side effects, so a flu shot while you're well should be your first choice. 
 
 “It can take up to two weeks to build full immunity to the flu after you are vaccinated," said Dr. Cara Christ, director of the Arizona Department of Health Services. "So I encourage everyone who has not yet had a flu shot to get one today before the holidays.” 
 
 Contributing: Megan Janetsky, The Arizona Republic; Joe Szydlowski, The Salinas Californian; Maddy Lauria, The (Wilmington, Del.) News Journal; Liv Osby, The Greenville (S.C.) News; Andrew Fraser, St. Cloud (Minn.) Times; The Associated Press. Follow Rachel Ohm on Twitter: @rachel_ohm 
 
 Source: Centers for Disease Control and Prevention 
 
 Read or Share this story: https://usat.ly/2CiKbj1 ||||| All data are preliminary and may change as more reports are received. 
 
 An overview of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available at http://www.cdc.gov/flu/weekly/overview.htm. 
 
 Influenza activity remains elevated in the United States. Influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B viruses continue to co-circulate. Below is a summary of the key influenza indicators for the week ending January 12, 2019: 
 
 WHO and NREVSS collaborating laboratories, which include both public health and clinical laboratories located in all 50 states, Puerto Rico, Guam, and the District of Columbia, report to CDC the total number of respiratory specimens tested for influenza and the number positive for influenza by virus type. In addition, public health laboratories also report the influenza A subtype (H1 or H3) and influenza B lineage information of the viruses they test and the age or age group of the persons from whom the specimens were collected. 
 
 Additional virologic data, including national, regional and select state-level data, can be found at: http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html. Age group proportions and totals by influenza subtype reported by public health laboratories can be found at: http://gis.cdc.gov/grasp/fluview/flu_by_age_virus.html. 
 
 The results of tests performed by clinical laboratories are summarized below. 
 
 Week 2 Data Cumulative since 
 
 September 30, 2018 (Week 40) No. of specimens tested 31,051 407,503 No. of positive specimens (%) 3,856 (12.4%) 26,430 (7.3%) Positive specimens by type Influenza A 3,730 (96.7%) 30,028 (94.5%) Influenza B 126 (3.3%) 1,752 (5.5%) 
 
 The results of tests performed by public health laboratories are summarized below. 
 
 Week 2 Data Cumulative since 
 
 September 30, 2018 (Week 40) No. of specimens tested 1,399 21,296 No. of positive specimens* 752 7,035 Positive specimens by type/subtype Influenza A 743 (98.8%) 6,789 (96.6%) (H1N1)pdm09 605 (89.1%) 5,214 (81.6%) H3N2 74 (10.9%) 1,173 (18.4%) Subtyping not performed 64 411 Influenza B 9 (1.2%) 237 (3.4%) Yamagata lineage 4 (100%) 110 (59.5%) Victoria lineage 0 (0%) 75 (40.5%) Lineage not performed 5 52 
 
 Influenza Virus Characterization: 
 
 Close monitoring of influenza viruses is required to better assess the potential impact on public health. CDC characterizes influenza viruses through one or more tests including genomic sequencing, hemagglutination inhibition (HI) and/or neutralization assays based Focus Reduction assays (FRA). These data are used to compare how similar currently circulating influenza viruses are to the reference viruses used for developing new influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. Antigenic and genetic characterization of circulating influenza viruses gives an indication of the influenza vaccine's ability to induce an immune response against the wide array of influenza viruses that are co-circulating every season. However, annual vaccine effectiveness estimates are needed to determine how much protection was provided to the population by vaccination. 
 
 For nearly all influenza-positive surveillance samples received at CDC, next-generation sequencing is performed to determine the genetic identity of circulating influenza viruses and to monitor the evolutionary trajectory of viruses circulating in our population. Virus gene segments are classified into genetic clades/subclades based on phylogenetic analysis. However, genetic changes that classify the clades/subclades do not always result in antigenic changes. “Antigenic drift” is a term used to describe gradual antigenic change that occurs as viruses evolve changes to escape host immune pressure. Antigenic drift is evaluated by comparing antigenic properties of cell-propagated reference viruses representing currently recommended vaccine components with those of cell-propagated circulating viruses. 
 
 CDC has antigenically or genetically characterized 562 influenza viruses collected September 30, 2018 – January 12, 2019, and submitted by U.S. laboratories, including 341 influenza A(H1N1)pdm09 viruses, 163 influenza A(H3N2) viruses, and 58 influenza B viruses. 
 
 Influenza A Viruses 
 
 A (H1N1)pdm09: Phylogenetic analysis of the HA genes from 341 A(H1N1)pdm09 viruses showed that all belonged to clade 6B.1. One hundred thirty-six A(H1N1)pdm09 viruses were antigenically characterized, and 134 (98.5%) were antigenically similar (analyzed using HI with ferret antisera) to A/Michigan/45/2015 (6B.1), a cell-propagated A/Michigan/45/2015-like reference virus representing the A(H1N1)pdm09 component for the 2018-19 Northern Hemisphere influenza vaccines. 
 
 A (H3N2): Phylogenetic analysis of the HA genes from 163 A(H3N2) viruses revealed extensive genetic diversity with multiple clades/subclades co-circulating. The HA genes of circulating viruses belonged to clade 3C.2a (n=48), subclade 3C.2a1 (n=78) or clade 3C.3a (n=37). Six A(H3N2) viruses were antigenically characterized by FRA with ferret antisera, and all 6 (100%) A(H3N2) viruses tested were well-inhibited (reacting at titers that were within 4-fold of the homologous virus titer) by ferret antisera raised against A/Singapore/INFIMH-16-0019/2016 (3C.2a1), a cell-propagated A/Singapore/INFIMH-16-0019/2016-like reference virus representing the A(H3N2) component of 2018-19 Northern Hemisphere influenza vaccines. 
 
 
 
 Influenza B Viruses 
 
 B/Victoria: Phylogenetic analysis of 18 B/Victoria-lineage viruses indicate that all HA genes belonged to genetic clade V1A, however genetic subclades which are antigenically distinct have emerged. Genetic subclades which are antigenically distinct include viruses with a two amino acid deletion (162-163) in the HA protein (V1A.1, previously abbreviated as V1A-2Del) and viruses with a three amino acid deletion (162-164) in the HA protein (abbreviated as V1A-3Del). Eight B/Victoria lineage viruses were antigenically characterized and 4 (50%) were antigenically similar with ferret antisera raised against cell-propagated B/Colorado/06/2017-like V1A.1 reference virus. Four (50%) reacted poorly (at titers that were 8-fold or greater reduced compared with the homologous virus titer) and belonged to clade V1A. 
 
 B/Yamagata: Phylogenetic analysis of 40 influenza B/Yamagata-lineage viruses indicate that the HA genes belonged to clade Y3. A total of 33 influenza B/Yamagata-lineage viruses were antigenically characterized, and all were antigenically similar to cell-propagated B/Phuket/3073/2013 (Y3), the reference vaccine virus representing the influenza B/Yamagata-lineage component of the 2018-19 Northern Hemisphere quadrivalent vaccines. 
 
 The majority of U.S. viruses submitted for characterization come from state and local public health laboratories. Due to Right Size Roadmap considerations, specimen submission guidance to laboratories is that, if available, 2 influenza A(H1N1)pdm09, 2 influenza A(H3N2), and 2 influenza B viruses be submitted every other week. Therefore, the numbers of each virus type/subtype characterized should be more balanced across subtypes/lineages but will not reflect the actual proportion of circulating viruses. In the figure below, the results of tests performed by public health labs are shown on the left and CDC sequence results (by genetic clade/subclade) are shown on the right.
– The warnings came early that this year's flu season could be bad, and reports starting to filter in from the Centers for Disease Control and Prevention suggest that prediction may have been an accurate one. Per the CDC, public health experts from 36 states have submitted reports indicating "widespread influenza activity," with a large number of cases in 21 of those states, USA Today reports. Epidemiologists are pointing to the reduced efficacy of this year's vaccine as one factor for the flu's early kickoff, with just a 10% to 33% effective rate. "Any time there's a mismatch between the vaccine and the circulating strain of the flu, you're going to see more cases," says a University of Tennessee Medical Center infection expert. The CDC is recommending people not only get the flu vaccine, but also take neuraminidase inhibitor (NAI) antivirals if they do get the illness, Medscape reports.