a_monster_representing_an_influenza_virus_hitting_a_man_over_wellcome_v0015684When flu is on the rise, so too is the quantity of information and misinformation spread about in coffee shops, school cafeterias, or online. Kids tell their friends that the vaccine is lethal, and websites warn of government conspiracies. (I know, mild stuff compared with the fake-news and falsehoods flying around the airwaves.)

Aside from the more dire claims, one assumption is that you can get sick from the vaccine. But flu shots contain only pieces of the virus or inactivated virus and cannot cause flu. And the nasal vaccine contains a weakened form of the virus which may cause some mild and brief discomfort, though nothing like full-blown flu. It is true that vaccinated individuals may end up with the flu; perhaps they were exposed within the two-week window it takes the vaccine to become fully effective, or maybe the vaccine was not 100 percent effective against a particular flu, or they may not have mounted a strong response. The flu vaccine is the least likely cause of illness.

Flu is a slippery beast. There will always be a new flu, because the viruses have particularly high rates of mutation and because the human immune system is incredibly good at what it does, which puts the pressure on flu viruses to evolve—naturally. This relationship between virus and immune response is ancient. And once flu takes hold in a population it can spread around the world in a blink of the eye. Antivirals may help calm the storm, but they too are often bested by rapidly evolving influenza. For those who are most susceptible, prevention can be a lifesaver.

While “I have the flu” has become a catchall for anything from a stomach bug to a cold to the real deal, it is only when we are really struck by the flu that we learn the distinction. Actual influenza is not a little queasiness in the gut, or the low fever that we tolerate as we go about our jobs. Flu can knock us off our feet. The worst flu viruses kill us. The infamous Spanish flu pandemic of 1918 is estimated to have taken 50 million lives worldwide, possibly killing more soldiers during World War I than did the bullets and bombs.

Even so, not all flu viruses are equally hazardous to our health. There are three types of influenza virus of varying capacity to make us sick: influenza A, B, or C. The flu that causes us to line up for vaccines, compulsively wash our hands, or take to our beds is influenza A or B. On the other hand, we are likely to mistake influenza C for a cold. Both A and B are relatively simple, each comprised of eight RNA segments carrying the necessary information for building new viruses. Encoded in these segments are instructions for two influenza proteins that are the bane of our existence: hemagglutinin (HA) and neuraminidase (NA). Because they don’t have all the bits necessary to reproduce on their own, viruses need growing cells—or more specifically, a healthy cell’s machinery. Once flu virus finds its way to its target cell, HA acts like a socialite’s calling card allowing the virus to slip its RNA into the cell without causing undo harm.

Should I become infected, my respiratory cells will quickly become subservient to the virus. Like a Xerox copier gone berserk, my own cells will churn out thousands to millions of copies of viral RNA. New viruses will be assembled and packaged, ready to be sent out into the world. This is where NA comes in. Just as HA enabled the entry, NA allows the next-generation viruses to be released from the cell’s membrane. As new viruses burst forth, my respiratory cells will be left in tatters. And I will take to bed, achy and feverish. As someone with mild asthma, flu is a complication I don’t need. Which is why one goal this early December weekend will be to visit the local Rite Aid for my annual flu shot. How about you?

Adapted from Unnatural Selection, Island Press, 2014.