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Jan 15, 2013 5:58 PM by Ryan Jaslow - CBS News

The flu vaccine: Why you should get one now

Get a flu vaccine, it's not too late.

That's the recommendation being urged by federal health officials, local doctors and most experts who are commenting on this year's flu epidemic. But what exactly is in the flu vaccine, what forms does it come in, and why should we get vaccinated if there's still a chance we can get sick?

Last week, the flu reached "epidemic levels," with 7.3 percent of all U.S. deaths caused by flu and pneumonia. Government estimates show 47 states are reporting widespread illness -- meaning at least 50 percent of its counties or subregions are reporting infections -- and high activity of influenza-like illness has been reported in 24 states and New York City. Officials expressed hope the flu may have peaked in some regions, but noted the severity of flu season is unpredictable.

That's why people are being urged to get the flu vaccine, which the government calls the best way to prevent flu.

A new flu vaccine is developed every year in an attempt to provide the best chances to reduce risk of getting the flu or spreading the illness to others. So even for those who feel they won't get sick from the flu, experts note they should still get vaccinated because they may pass flu on to other people who are more at risk, such as young children, the elderly or persons with other medical conditions that weaken immunity.

The vaccines protect against infection and illness caused by the three influenza viruses -- or strains -- that a panel selects each year based on research that indicates which will be most common this season.

This year's vaccine contains two influenza A strains and one influenza B strain, Dr. William Schaffner, the chair of preventive medicine at Vanderbilt University who was immediate-past president of the National Foundation for Infectious Diseases, told CBSNews.com Tuesday. The A strains include an H1N1 strain similar to the one that caused a 2009 "swine flu" pandemic and a new H3N2 strain that is actually the strain that is causing most of the damage now, according to Schaffner, who served on the CDC panel that helped pick which strains would go into this year's vaccine.

"So that was a bull's-eye hit," he said.

The influenza B strain included in the vaccine is similar to a 2010 strain, but Schaffner said there is typically more than one B strain "smoldering" during flu season. While this vaccine targets one of them, he said, there's another strain out there causing about 6 to 8 percent of the disease, and this year's vaccine won't protect flu caused by that virus.

However, just because you get vaccinated doesn't mean you'll evade the flu.

A recent CDC study found this year's vaccine is about 62 percent effective, meaning it will prevent disease completely 62 percent of the time, according to Schaffner.

"It means that the glass is more than half full," he said. "It's not a perfect vaccine, but a good vaccine."

Even when the flu vaccine does not prevent a person from getting sick, it can lead to milder illness or prevent complications including pneumonia and even death.

Once vaccinated, the body takes about two weeks to develop flu-fighting antibodies, meaning people are still at risk for flu after they get the vaccine. That's why experts recommend vaccination early in the fall before flu season -- which typically peaks in late January or February -- gets under way. The vaccine's protection lasts through the spring, according to the CDC, so people need to get it every year. People who already got vaccinated this fall should not try to get another flu shot amid the reports of a flu epidemic.

There are two types of flu vaccines available for Americans, according to the CDC: the "flu shot" and the nasal spray vaccine. A flu shot contains a killed flu virus that is given with a needle, typically in the arm. All people ages 6 months and older, including healthy people, those with chronic medical conditions and pregnant women are recommended to get a flu shot.

This year, there are three different types of flu shots available. A regular flu shot approved for people ages 6 months and older, a high-dose flu shot designed for people 65 and older (the higher dose is meant to give the elderly better protection because immunity weakens with age) and an intradermal flu shot approved for people 18 to 64 years of age that is injected into the skin, rather than the muscle as is typical for the other shot formulations. The latter shot has a needle 90 percent smaller than those used for typical flu shots, and may cause redness but not the soreness that may accompany the regular flu shot's deeper muscle injections.

As for FluMist nasal sprays, these vaccines are made with live, weakened flu viruses that enter the body by being pumped through the nose. The viruses in the nasal spray vaccine do not actually cause the flu even though they are "live," because they are designed to only work in cooler temperatures of the nose and not warmer areas like the lungs. This vaccine is approved for use in healthy people ages 2 through 49 who are not pregnant and don't suffer from egg allergies or other chronic medical conditions. Schaffner noted children sometimes prefer these vaccines because doctors don't have to bring out needles; some adults prefer the sprays for that same reason, he said.

Generally, people who should not get vaccinated include those who are allergic to chicken eggs or have had a severe reaction to influenza vaccination in the past, children younger than 6 months of age and people who are already sick with a fever, who should wait to recover before they are vaccinated. People with Guillain-Barr? Syndrome, a severe illness that could lead to muscle weakness and paralysis, should also speak to a doctor to help decide whether to take the vaccine.

Some critics have taken issue with the vaccine being only 62 percent effective, or the fact that many people who have taken it are still getting sick.

Dr. Adam Stracher, director of the primary care division of the Weill Cornell Physician Organization at Weill Cornell Medical College, told CBSNews.com that the vaccine is safe, and a much better option than not getting any vaccine.

"While it may not be 100 percent effective, even in those patients who get the flu after getting the flu vaccine, they tend to have a milder illness than patients who haven't gotten the flu vaccine," he said.

Stracher adds that despite some common fears it's impossible to get the actual flu from the vaccine because it's only made of a component of the virus, but people can feel aches or a low-grade fever following vaccination as a response to a foreign protein being injected into the body.

Schaffner adds that less than 1 percent of people get a fever from the shot, and the nasal spray vaccine may lead to a runny nose or sore throat, but none of these things are considered a serious flu infection. He was blunt when assessing the common fears that the flu shot can cause the flu:

"That's malarkey," he said.

Improvements to the vaccine may also be on the horizon to improve future formulations.

CDC officials have discussed some potential improvements coming down the pike, including a quadrivalent vaccine that protects against four flu strains instead of three, and new cell-based flu vaccines, Flucelvax, which recently became FDA-approved in November.

The traditional method to create a vaccine involves virus samples being injected into specialized chicken eggs which are then incubated. Egg fluids are later harvested and purified into the vaccine. The new technology involves small amounts of virus which is placed into fermenting tanks with nutrients and animal cells. The virus is then deactivated, purified and put into vaccine vials, a method officials believe is faster than egg-based production and could speed up manufacturing in the event of a pandemic.

In December, Dr. Michael Osterholm, an infectious disease specialist who has studied medical records and flu studies dating back to the 1930s, told CBS News correspondent Elaine Quijano that growing viruses in chicken eggs is slow, inexact and outdated.

"If we don't change our current vaccines, we will have some protection, but we will in two ways miss two very important goals: one, protecting old people at the highest risk of death and two, when the next pandemic emerges, we will miss the opportunity to protect against pandemic," he said at the time. Despite his concerns, he recommended people get the vaccine because it's safe, and some protection is better than none.

Schaffner also mentioned that doctors are investigating "universal" flu vaccines that would be capable of preventing all flu strains that people would only need to get once every 10 years. Dr. Francis Collins, chief of the National Institutes of Health, confirmed the vaccine's development in Dec. 2011.

However, until then, people should get the current vaccine which is safe, said Schaffner, who paraphrased Voltaire for his message:

"Waiting for perfection is the greatest enemy of the current good," he said.

The CDC noted during a conference call last week that there are spot shortages of this year's vaccine based on some reports it has received. The agency's website directs people to the HealthMap Vaccine Finder where people can plug in their zip code. Users are also asked to report any vaccine shortages they may experience through this website or tweet @vaccinefinder on Twitter with the hashtag #vaxshortage.

© 2013 CBS Interactive Inc. All Rights Reserved.

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