Influenza: So S’not Funny

Emily BurkeEdited by Sarah Van Tiem, Immunology, Infectious disease

Influenza: So S’not Funny

Happy Flu Season! A throbbing headache, fever, chills—if you’ve ever enjoyed a few days off courtesy of influenza, you’ve got good reason to embrace the simple flu shot. Every year, millions of us roll up our sleeves and take our medicine. This WEEKLY reviews the ABCs of the flu virus and what you need to know about the vaccine.

The US Centers for Disease Control (CDC) (Atlanta, GA) estimates that about 170 million doses of influenza vaccine will go to doctors’ offices, health departments, and even the corner drugstore to help keep people flu-free during 2018-19. Drug companies deal with this high demand by making the vaccines six to nine months before flu season starts in October.

A is for Awful

Last year’s flu season was terrible—and not just for the young, elderly, and immunocompromised, all of whom are especially prey to the illness. The CDC tallied a record number of flu-related hospitalizations. Sadly, the season also killed 80,000 people in the US alone. That’s the highest number of flu-related deaths since the CDC began tracking flu mortality in 1976 (CDC).
Like all viruses, a flu bug has a simple structure. It consists of eight strands of RNA – its genetic material – surrounded by a protein capsid, all nestled within a lipid envelope. With influenza, the RNA encodes 11 genes, each of which produces a different protein.

How does a seemingly inconsequential little microbe wreak such havoc? Irritatingly, most of the illness’s misery results from our own bodies trying to defend us.

B is for Body Slam

The flu virus uses proteins on its surface to dock onto and invade our lung cells. Once inside, the pathogen highjacks cellular machinery to replicate itself. The copies are then released to invade the nearest neighbors. This process does damage lung cells somewhat. But most symptoms actually stem from the immune response itself. Viral replication attracts T-cells. To stamp out the threat, these warrior cells do what they do best: kill infected cells. The cellular death damages our lungs and kicks mucus production into high gear. Voila—cough, cough hack, sneeze, yuck. All of this unpleasantness is good though. It means your poor aching body is trying to get rid of flu filth.

Activated T-cells also release inflammatory cytokines – signaling molecules that further rev up immune response, sending more white blood cells to attack the infection. Cytokines also contribute to symptoms. For example, some affect the region in the brain’s hypothalamus that controls temperature, leading to fever and headache. Others get into our muscles. In fact, research indicates that inflammatory cytokines break down muscle tissue by switching on muscle-degrading genes – leading to, you guessed it, muscle aches.

Although our immune response makes us miserable, we are far better off with than without it. The elderly or other immunocompromised flu sufferers experience more damage to lung cells than younger, more robust folk. Unfortunately, that means they are far more likely to suffer complications, such as secondary infections like bacterial pneumonia.

Not All Body Slams are Alike

A few years ago, you may have heard of the H1N1 flu. What’s up with the letters? “H” refers to the protein hemagglutinin, which is present on the virus surface. It facilitates entry into host cells. “N” stands for neuraminidase, another surface protein. It enables the release of new viral particles from infected cells.

Hemagglutinin and neuraminidase both have variations. Particular combinations are identified by number. Hence H1NI or H3N2, for example. Certain combinations seem to make some flu seasons worse. Scientists are still trying to figure out why. Theories include the possibility that it’s more difficult to develop a reliable vaccine against certain influenza strains or the fact that some types of hemagglutinin target more tissues, resulting in nastier symptoms.

C is for Common Sense: Get Your Vaccine

The best way to avoid the flu is to get vaccinated. The idea behind vaccination is simple. Exposing the immune system to an inactivated virus “trains” it to quickly recognize the real thing in the future.

Most vaccines are close to 100% effective. Alas, flu vaccines are more typically about 60% effective. This is because the flu mutates considerably from season to season. CDC epidemiologists work hard to predict the most prevalent strain of the virus for the upcoming season; however, these predictions are notoriously tricky. Regardless though, flu vaccines offer protection. They do not, repeat, do not –make people sick, no matter what you may hear otherwise at the water cooler. Some people do feel minor symptoms associated with the vaccine, such a slight fever or headache. These actually mean that the vaccine is kicking in and prodding the body’s immune response into action.

Good News on the Horizon

A number of different biotech companies are working towards a “universal flu vaccine.” This shot could be given once every five years or so and be more effective than annual vaccines. Next week, we look at the technology behind these vaccines, as well as review some new flu drugs in development. In the meantime, sneeze into your elbow, wash your hands and get that flu shot!