It's official: Flu season is in full swing. In fact, according to data from the Centers for Disease Control and Prevention, the number of positive influenza tests reported to the CDC have increased each week for about three consecutive months. That streak was broken during the fourth week of 2017, but that doesn't mean that influenza worries should be placed on the back burner.

While the flu is a nuisance for most Americans, it can be a matter of life or death for children, who have less-developed immune systems, and the elderly, whose immune systems can be compromised. Mortality data from the CDC in 2015 showed that influenza and pneumonia are the eighth leading cause of death in the United States, directly claiming more than 55,200 lives. And, as you can see from the CDC data below, the pneumonia and mortality rate in the 2016-2017 flu season just crossed into the epidemic threshold territory.

CDC chart showing flu mortality rates have risen above the epidemic threshold for the 2016-2017 flu season

Image source: Centers for Disease Control and Prevention.

Influenza is hitting hard, but here's the real surprise

Each year, between 4,000 and 50,000 people are specifically killed by influenza, and most commonly it's caused from a variation of an influenza A strain virus. Influenza B strains tend to occur later in the season and be of the more mild variety.

Unquestionably, the flu is hitting harder this season than it did in the previous year, but this isn't a big surprise. What could arguably be the bigger shock is that researchers appear to have hit the nail on the head once again when it comes to predicting the dominant flu strains months in advance of flu season. 

As you can see below, a majority of the positive influenza tests this flu season have come back as an influenza A H3N2 variant, with a relatively smaller number of H1N1 and influenza B strain viruses. One of the primary strains that this year's flu vaccines focused on was H3N2. It'll still probably be a few weeks before there's an official reading on the effectiveness of this year's vaccine, but there's a pretty good chance that'll it'll be within range or above the usual vaccine effectiveness of 50% to 60%.

CDC chart showing all positive influenza cases have been of the H3N2 strain

Image source: Centers for Disease Control and Prevention.

Understandably, researchers aren't always going to be right in predicting the dominant flu strains. Vaccines are usually developed in the summer, months ahead of the actual flu season. If vaccine developers guess wrong, there's just not enough time to start from scratch and manufacture enough vaccines to protect the consumer. But more often than not, researchers have done a pretty good job of guessing the correct strains to focus on.

The simple way Americans could keep flu deaths down in 2016-2017

The real disappointment can be found when looking at the number of U.S. adults who get a flu shot. Rough estimates for the current flu season suggest that somewhere around 40% of Americans got the flu vaccine, leaving a majority of people potentially exposed to the flu's deadliest strains. On average, between 40% and 50% of adults get a flu shot every year.

Why don't people get a flu shot? While the answer likely varies from person to person, one of the prevailing ideas is that it doesn't work, fueled by the belief that getting a flu shot should keep you from getting the flu. But that's not the intended purpose of the flu shot.

A flu vaccine is designed to lessen the severity of influenza and reduce the chances of a person winding up in the hospital. If anything, it's the perfect immune system booster for younger, healthier adults. This allows hospital staff to direct their attention to the elderly, who are the most likely to be seriously compromised by the flu.

Woman sick in bed

Image source: Getty Images.

There's also the prevailing myth that getting a flu shot will give you the flu, which isn't true. With the exception of AstraZeneca's (NYSE:AZN) live attenuated vaccine known as FluMist, the other vaccines are comprised of inactive flu strains. Think of them as a teaching tool for your immune system so it understands how to fight the flu should you be infected. Even if you take AstraZeneca's FluMist, the dosage is low enough to not cause someone to develop the flu. At worst, the patient will come down with minor cold symptoms.

Presumably, if more people got a flu shot, there could be fewer flu-related deaths each year.

The proliferation of new vaccines offers promise

The researchers that develop seasonal flu vaccines have been focusing on a new type of flu vaccine in recent years known as a quadrivalent. Previous vaccines before the quadrivalent focused on three strains each year: two influenza type A strains and a single type B strain (and were thus known as trivalent vaccines). The new quadrivalent vaccines, which have been on the market for a few years and are beginning to grow in use, combine two type A and two type B strains. The hope is that these new vaccines will provide better vaccine effectiveness in the later half of flu season when type B strains are more prevalent.

There are a number of quadrivalent options for consumers to choose from this season. One option that is available -- but which the CDC suggests you steer clear -- is AstraZeneca's nasal spray FluMist. Despite being a handy alternative to getting a shot, studies have suggested that FluMist simply isn't effective compared to the other flu vaccines being offered.

Doctor administering a flu vaccine to an elderly patient

Image source: Getty Images.

The most popular flu vaccine year in and year out continues to be Sanofi's (NYSE:SNY) FluZone, which has topped the $1 billion sales mark in previous years depending on the severity and public worry surrounding the flu.

There are three aspects of FluZone that allow it to stand out head and shoulders above its peers. First, FluZone is approved to treat infants as young as six months old. Many of Sanofi's peers have considerably higher lowest-age treatment recommendations. Second, FluZone has a dosing option that features a needle that's 90% shorter than a traditional needle, which a nice option for those who are needle-phobic, and for children. Lastly, FluZone isn't a one-size-fits-all vaccine. There are around a half-dozen different dosing options, which makes it a preferred choice of physicians.

The flu vaccine is never going to be perfect, nor is it ever going to be able to prevent people from getting the flu. However, the data would suggest it does a good job more often than not of reducing the severity of the disease in people should they come down with the flu.

Sean Williams has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.