The flu epidemic sweeping the United States has caused a notably high number of deaths. Now officially “widespread” in 49 U.S. states — all of them except Hawaii — the flu virus has directly or indirectly caused a proportion of deaths that the U.S. Centers for Disease Control and Prevention consider “above the epidemic threshold,” according to a report released by the agency on Friday. In a teleconference on Friday, federal officials said that this flu season is the worst one to hit the U.S. since the 2009 swine flu pandemic swept the country, citing the current epidemic’s rising hospitalization rate.

This week alone, seven children died, bringing the total of pediatric deaths since the flu season began in October to 37. Even though we’re in the midst of the flu season, however, it isn’t too late to protect yourself. The CDC says that getting your flu shot is as important now as ever.

Part of the reason the current epidemic is so intense is because it’s dominated by influenza A(H3N2), the most dangerous of the four seasonal flu strains. However, just because H3N2 is the dominant strain doesn’t mean that it’s the only one that will show up this season. Joining H3N2 among the influenza A strains is another strain called H1N1, and influenza B has two lineages, B/Yamagata and B/Victoria. The influenza B viruses tend to show up later in the flu season than the influenza A viruses.

flu shot 2018
This year's flu shot confers protection against the current dominant strain, as well as three others that may show up later this season.

In an interview with CNN on Wednesday, CDC Domestic Flu Surveillance team head Lynette Brammer said, “We want to continue to emphasize that there’s still a lot of flu activity to come, people that haven’t been vaccinated should still get vaccine. We may be getting close to the peak of this wave, it’s not unusual to have a second wave of influenza B come through.” The flu shot, though imperfect, confers some degree of protection against all four seasonal flu strains.

Earlier this flu season, a preliminary analysis published in the New England Journal of Medicine estimated that this year’s vaccine is only 10 percent effective against H3N2, but the CDC has pointed out that this number was based only on data on the elderly and infirm, who are more likely to succumb to illness in the first place. Its actual effectiveness against H3N2 is closer to 32 percent, which is the same as what it was in the 2016-2017 flu season.

herd immunity flu shot vaccine influenza epidemic
This is how herd immunity works.

This may not seem like an especially high success rate, but as Inverse has discussed before, widespread vaccination is the only way to stop a virus from spreading. When everyone gets the flu shot, the population gains “herd immunity,” which makes it harder for the particularly vulnerable among us — children and the elderly — to catch the virus:

In general, viruses spread by finding a host, incubating and multiplying inside that host, then bursting outward from that host — through sneezes, snot, and spit — into the mucus membranes of other potential hosts, kicking off the cycle all over again. The point of a vaccine is to train the immune system to kill flu virus particles ahead of time so that when a person does encounter the flu virus, the body can kill it before it has the chance to spread.

When you don’t get vaccinated, you give the flu a free pass to use you as a breeding ground, putting other people — the babies, old people, moms-to-be, and the sick we mentioned before — at risk of becoming gravely ill. In contrast, when enough people get vaccinated, they produce what’s known as “herd immunity” — a form of population-wide protection against an infectious disease caused by the inability of the virus to find any hosts in which they can settle.

The CDC is reluctant to speculate on what will happen this flu season — there’s just not enough data to tell — but for now, the same rules for protecting yourself and everyone around you apply: In addition to getting vaccinated, wash your hands and belongings thoroughly, wipe down often-used surfaces like door handles and remotes, and, if you do happen to catch the flu, stay home.


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