Here’s what you should know about the flu season this year

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What does the flu do to the human body?

Here's a look at how the flu virus infects the body and produces symptoms. (Joyce Koh/The Washington Post)

This year's flu season is already the most widespread on record since health officials began keeping track 13 years ago, and has already caused the deaths of more children than what normally would be expected at this time of the year, federal health officials have said.

During the second week of January, more people sought care for flulike illnesses than at any comparable period in nearly a decade, the Centers for Disease Control and Prevention's most recent weekly report shows. Ten children died in the week ending Jan. 13, bringing the total number of pediatric deaths this flu season to 30. More than 8,900 people have been hospitalized with laboratory-confirmed influenza since the season started Oct. 1. The flu activity indicators are notable for the sheer volume and intensity of flu that is taking place in most of the country at the same time.

Reporter Lena H. Sun has been talking to health officials over the past several weeks about this flu season. Here are some answers to frequently asked questions:

Q: What's going on with the flu this season?

This flu season started early, and the entire country is experiencing widespread and intense flu activity. The data show there's been a very rapid increase in the numbers of people going to see their doctors or health-care providers.

Q: Is there something particularly bad about this year's flu strains?

This season, the predominant strain is also the nastiest, H3N2, which causes the worst outbreaks of the two influenza A viruses and two types of influenza B viruses that circulate among people and are responsible for seasonal flu epidemics each year. Seasons when H3N2 strain dominates are associated with more hospitalizations, more deaths and more illnesses. Those who are particularly hard hit are the very young, the elderly and people with certain chronic health conditions, experts say.

As top CDC flu expert Daniel Jernigan said: “Of the viruses we hate, we hate H3N2 more than the other ones.” This strain, which has been around for 50 years, is able to change more quickly to get around the human body’s immune system than the other viruses targeted in this year’s seasonal flu vaccine.

The CDC estimates that flu has resulted between 9.2 million and 35.6 million illnesses and 12,000 to 56,000 deaths each year in the United States since 2010.

Q: Are there any differences in flu symptoms this season?

No. Flu symptoms vary from person to person. In general, people who have the flu often feel some or all of these symptoms, according to the CDC:

• Fever or feeling feverish/chills (not everyone with flu will have fever)
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue (tiredness)
• Vomiting and diarrhea, although this is more common in children than adults

Most people who get the flu get better in several days to less than two weeks. But some people can develop serious complications caused by viral infection of the nasal passages and throat and lungs. Young children, adults ages 65 years and older, pregnant women, and people with certain chronic medical conditions are among those groups of people who are at high risk of serious flu complications, possibly requiring hospitalization and sometimes resulting in death.

Q: How effective is this year's vaccine?

The CDC and clinicians recommend a yearly flu vaccine for everyone 6 months of age and older as the first and most important step in protecting against this serious disease. The body takes about two weeks to produce a full immune response. Flu vaccination can reduce illness and prevent flu-related hospitalizations. A study in Pediatrics last year was the first of its kind to show that vaccination lowered the risk of flu-associated death by half among children with underlying high-risk medical conditions and by nearly two-thirds among healthy children.

But flu vaccines aren't perfect. Even in a good year, the flu vaccine isn’t as good as most other vaccines. Health officials must choose the influenza strains that vaccine makers should target for an upcoming season months in advance, when it is hard to know what strains might be circulating. When flu vaccines are well matched to circulating viruses, effectiveness is, at best, about 60 percent. (The measles vaccine, by comparison, is about 97 percent effective with two doses.) In a year when the circulating flu strains closely match the vaccine, that effectiveness rate means that about 3 in 5 people who get shots are far less likely to become so sick that they require a visit to a doctor.

In general, flu vaccines tend to work better against influenza B and influenza A(H1N1) viruses and offer lower protection against influenza A(H3N2) viruses.

Q: How long will this flu season last, and when will it peak?

Flu is very unpredictable. The exact timing and duration can vary, but influenza activity often begins to increase in October. Most of the time, flu activity peaks between December and February, although activity can last as late as May. Experts aren't sure when this season will peak. Officials were hoping the season had peaked in the first week of January, but the latest data shows activity continued to increase into the second week. Even if flu activity peaks soon, there will probably be many more weeks of flu activity based on patterns of similar seasons when this particular strain has dominated. In those seasons, flu season lasted for at least 11 to 13 more weeks after activity hit the peak. The overall hospitalization rate for the week ending Jan. 13 is now 31.5 per 100,000 people, up from 22.7 per 100,000 the week before.

Q: What flu symptoms should parents watch for in their children?

Patsy Stinchfield, a pediatric nurse practitioner and senior director of infection prevention and control at Children's Hospitals and Clinics of Minnesota, said parents should call or bring their children to see the doctor early if the children aren't drinking, are really lethargic, have pain in a specific place in their chest or are having difficulty breathing after normal activity, such as going upstairs. Also, if they are getting better and suddenly get worse, bring them in to the hospital right away, because this could be a sign of a secondary bacterial infection.

“These kids don't do well when brought in late for care,” she said.

These stories about a 6-year-old and a 10-year-old who died recently of flu show how dangerous the disease can be.

Q: Some news reports have claimed the flu vaccine is expected to be only 10 percent effective this year; is this true?

U.S. officials often look to Australia, where the flu season begins during our summer and their winter, for clues on what to expect for flu in the United States. Flu virus infections began increasing earlier than usual in Australia, hitting historic highs in some areas, and interim reports suggested that vaccine effectiveness against H3N2 was only 10 percent. The vaccine for the United States has the same composition as the one used in the Southern Hemisphere.

But Australia vaccinates only the elderly and infirm, who generally don’t respond as well to vaccines. Its approach makes a difference in vaccine effectiveness rates because children have better responses. CDC officials said a better predictor of vaccine effectiveness for H3N2 is last season's vaccine's effectiveness in the United States. The current vaccine contains the same H3N2 component as last season, which was about 32 percent effective.

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The deadly flu strain hits every state

This year’s seasonal flu epidemic is especially severe, according to the Centers for Disease Control, which says the deadly virus is now in every U.S. state. (Reuters)

Q: Should I still get a flu shot?

Yes. Experts say there are other strains of flu that are showing up and are a major cause of disease. Influenza B viruses, which this year's vaccine also covers, are already showing up and tend to emerge later in the season. One of the other influenza viruses, H1N1, is appearing in states that have already had lots of H3N2 activity. Here is a vaccine-finder widget that can find locations that still offer the flu shot.

Q: What if I think I have the flu? What kind of treatment is available? 

Antiviral drugs such as Tamiflu can lessen the symptoms and shorten the duration of illness. Most people who get the flu have mild illness and don't need antiviral drugs. But people who are very sick or people with flu symptoms who are at high risk for serious complications should be treated as soon as possible with antiviral drugs. That means people 65 and older, young children, people with chronic conditions, such as diabetes, heart disease or asthma, and pregnant women and others more vulnerable to serious flu illness.

The CDC has been urging clinicians not to wait for confirmed testing but to begin treatment if they suspect flu in a severely ill or high-risk patient. Young children and children with high-risk conditions respond to Tamiflu best when it's given in the first 48 hours.

Also, if you or your children are sick, stay home from work or school to avoid spreading it to unsuspecting others, especially people who haveweak immune systems and are at higher risk.

Q: What can I do to avoid getting sick?

The single most important thing to do is prevent the spread of germs. Wash your hands frequently, soap up between your fingers and don’t forget your thumbs, and scrub for about 20 seconds. Some other good tips, as reported by my Washington Post colleague Jura Koncius:

Isolate toothbrushes. Once a household member has a cold, it’s best to separate their toothbrush from the rest of the pack to avoid germ contamination. After the person gets well, replace the toothbrush or toothbrush head with a new one.

Launder bedding frequently. The best thing to do if someone is sick is to put them in a separate room to sleep, preventing the spread of germs as well as preserving your precious sleep. If this isn’t possible and you must share the same bed, wash your sheets frequently in hot water. It even helps to wash just the pillowcases every few days. Bath towels should be washed every day or two.

Clean your humidifier. Humidifiers help soothe sinuses and nasal passages, especially when you have coughing and chest congestion. But if you are using your humidifier on a daily basis to make your patient feel better, once a day you should empty the tank and then wipe it down until it’s dry. Do a thorough cleaning of it at least weekly, following the directions provided for your particular model. “You don’t want germs breeding in there and spewing out into the room,” Carolyn Forte, director of the Good Housekeeping Home Appliances, Cleaning Products, and Textiles Lab, told The Post.

Keep the remotes wiped off. Flu sufferers are likely to spend long hours on the couch sniffling and feeling sorry for themselves, clicking through Netflix and HBO offerings. So all those remotes will be covered in germs. Keep a container of antibacterial wipes around so you can clean the remotes on a daily basis; clean your light switches and doorknobs with them, too. Put a small wastebasket in the TV room with a plastic liner for all the wet tissues and used wipes, and empty it once or twice a day.