What Makes the Flu So Bad this Year?

There has been much in the news lately about the severity of the flu this winter. Some have said it’s the worst flu since the swine flu pandemic of 2009 . At the start of 2018, the CDC noted that every state in the continental United States was reporting widespread influenza activity. This is the first time that has happened since influenza monitoring was put into place 13 years ago. Normally by the end of February and into March at least some states begin to show signs of a reduction in influenza cases. Thus far this year, no such slowdown is in sight.

So what makes this year’s influenza outbreak so widespread and extra deadly? The answer to that starts with an understanding of the biology of the influenza virus and how it’s named. Influenza is an RVA virus with an outer envelope surrounding the viral capsid. Proteins stick out of the envelope structure to assist with the life cycle of the virus. There are many specific strains of influenza due to different small variations of these proteins. There are 3 influenza groups, Type A, Type B and Type C, with Type A being the most common. Type A influenza has a pair of proteins used to identify specific strains, the H protein (hemagglutinin – 18 different types) and the N protein (neuraminidase – 11 different types).

Influenza strains are named for these two proteins, (the H and N proteins) as well as type, host, geographical origin and year of isolation.  The full name of a specific strain could be: A/California/7/2009 (H1N1)-like virus. Most often the H and N protein designation is used. For example, H1N1 is the strain that caused the swine flu in 2009. This year the predominant strain is H3N2 though there are reports of some H1N1 also appearing in some locales.

Since the immune system reacts to one specific type, a person can be infected year after year and never become immune to all of these different strains. To make matters worse, the strains mutate periodically to introduce even more variants. For this reason there is no way to get one vaccine that’s effective against every possible variant. Even if that were possible, new ones could always emerge to cause illness. This is known as antigenic drift, where small changes of the viral surface helps it to confuse the immune system making it harder to mount an effective response. In comparison, antigenic shift causes a large change in the virus surface structure. Sometimes a host organism can be infected with two separate strains at once and the viruses exchange genes to create something entirely new.

Consequences of Genetic Changes

When this happens the virus has virtually the entire population available to infect as no one has any immunity at all. This is what is believed to have happened in the great Spanish Flu of 1918. This is the 100 year anniversary of that pandemic in which a quarter of the world’s population got sick and up to 50 million died. Keep in mind, this was at a time when 16 million died fighting in WWI, a particularly vicious war. At that percentage of flu deaths relative to number of cases, a similar epidemic today would kill millions in America alone, and up to 200 million worldwide.

Building a Vaccine

Since that time we have learned much about viruses and how to control them. The CDC is tasked with tracking outbreaks in the US and around the world. Identifying and tracking specific strains in key to these efforts. Each year health authorities have to sit down and decide which strains to use in vaccines for next year. This decision has to be made months in advance to allow enough time to put the chosen vaccine into production. Since the virus is commonly grown in eggs it takes time to produce enough virus to use in a vaccine.

Some statistical work and careful estimating goes into choosing the 3 or 4 strains to go into each year’s vaccine. The problem is a new strain can emerge or a strain that did not appear to be a likely candidate then becomes the dominant one over the period of time between choosing strains and the rollout of the first batches of new vaccine.

This year the vaccine has not been as effective. Normally the flu vaccine is as much as 60% effective. Early estimates of the effectiveness of the current vaccine showed about 40% efficacy. The CDC has since reduced that number to 36%.   Health officials try to predict the likely strains for an upcoming flu season, but sometimes the vaccine is not as effective as expected. These are the strains used in the trivalent vaccine for the 2017-2018 season.

A/Michigan/45/2015 (H1N1)pdm09-like virus

A/Hong Kong/4801/2014 (H3N2)-like virus

B/Brisbane/60/2008-like (B/Victoria lineage) virus

When more virulent strains emerge, like the H3 variants, trips to the doctor go way up, the number of hospitalizations increase as does the death rate, especially for children and older adults. A bad influenza infection opens the lungs up to secondary, bacterial infections like pneumonia. Again, more hospitalizations and deaths ensue. When particularly aggressive strains come around at the same time a yearly vaccine that does not live up to expectations, the combination is extra deadly for susceptible groups like young children and older adults.

Even during years when the vaccine is not as effective, if a particularly virulent strain is going around, it becomes even more important to get a flu shot. It sounds contradictory but even a vaccine that is not 100% can impart some level of protection from some of the strains. Keep in mind in any given year, there are multiple strains moving through the population. When a bad one is mixed in, being immune to some of the strains will help keep the body in better shape to fight off a nasty strain if encountered. When one already has the flu and is then exposed to an even harsher strain, it makes things that much harder on the immune system. Extra complications can set in and deadly bacterial infections can then occur.

In the end, the tried and true way to keep from coming down with the flu is vaccination. Washing hands and wearing a mask can help keep one from getting the flu, once you do, it comes down to managing symptoms to prevent more serious complications. While drugs like Tamiflu can shorten the length and severity of an influenza infection it cannot prevent infection in the first place where a vaccine can.

There is hope in a new drug that may soon be available. This experimental drug has been shown to destroy the virus in around 24 hours, 3 times faster than Tamiflu. Even so, a patient still has to make an appointment to get the drug and wait a day or better to recover fully. Having a level of immunity up front is really the best defense. Only vaccination will provide that level of protection from both the flu itself and any secondary infections that could occur.

Additional resources:

Article by Michael Troyan, Ph.D.

Image Sources:

  • Virus Structure: Ricochet Creative Productions LLC
  • CDC Map
  • Flu Vaccine Technologies: By The U.S. Food and Drug Administration (Flu Vaccine Technologies) [Public domain], via Wikimedia Commons
  • Tamiflu image: By Pieria (Uploader and Photographer) (Pieria (Uploader and Photographer)) [Public domain], via Wikimedia Commons
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