Did the flu knock you off of your feet and keep you bedridden this year? Or are you surprised that you somehow avoided it altogether? In either case, a recent study in the journal Science suggests that your birth-year may determine which flu strain(s) will most likely infect us.
It probably feels like the Flu Gods have decided your fate but in the iconic words of Bill Nye, science rules because researchers hope this finding will help control the spread and impact of future influenza viruses.
What exactly are flu strains?
Influenza (aka Flu) viruses cause contagious respiratory illnesses that infect the nose, throat, and lungs. It is extremely challenging for scientists and medical professionals to prevent these viruses because they are generally understood to be spread through droplets and acts including coughing, sneezing, and talking. Depending on the severity of the illness, some people may suffer mild to severe symptoms and, in extreme cases, death.
Common signs and symptoms of the flu include:
- Chills (and sometimes fevers)
- Sore throats
- Muscle or body aches
- Runny or stuffy noses
- Vomiting and diarrhea.
These viruses are capable of affecting everyone, even people who lead pretty healthy lives. However, the flu tends to impact elderly people, young children, and individuals with vulnerable immune systems.(1)
Types of Flu Strains
Generally speaking, there are four types of flu: A, B, C, and D however, type D viruses relate primarily to cattle and aren’t thought to affect humans. Type C viruses result in less severe respiratory illnesses and scientists don’t believe they lead to pandemics. For Type B viruses, scientists divide them into two lineages (instead of sub-types) known as B/Yamagata and B/Victoria.
Almost every winter in America, A and B flu viruses cause epidemics; hence, flu season.
Type A Viruses: Two proteins exist on the surface of the virus: hemagglutinin (H) and neuraminidase (N). Based on these two proteins, scientists have divided Type A viruses into a total of twenty-nine subtypes: 18 H-subtypes and 11 N-subtypes (denoted by H1-18 and N1-11).(2)
One of the more recent and recognized Type A flu strains is, for example, the mutation of H1N1 virus that surfaced in 2009 and caused a global (swine) flu pandemic. You arrive at the proper naming and nomenclature with the following components:
- Antigenic type (e.g., A, B, C, or D)
- Original host (e.g., swine, chicken, etc. Human-origin viruses do not get host designations)
- Geography (e.g., Alberta, China)
- Strain Number (e.g., 15, 7)
- Year of Isolation (e.g., 2009)
- For Type A viruses, we put the hemagglutinin and neuraminidase descriptions in brackets
The “swine flu” above originated in swine, but scientists first found it in humans in Mexico. So, the proper naming and nomenclature would look like this: A/Mexico/1/2009 (H1N1).(3)
Can we protect against flu strains?
In a recent study called “Potent protection against H5N1 and H7N9 influenza via childhood hemagglutinin imprinting,”(4) ecology and evolutionary biology Professor Michael Worobey and his team analyzed the effects of first-time influenza attacks on children and how their subsequent immune system builds up.
What did they study?
Scientists analyzed data from over fourteen-hundred people of all ages who were affected by two Type A viruses that animals could transmit to humans (i.e., the avian influenzas H5N1 and H7N9). To their surprise, some people were immune to avian flu, which scientists previously believed to exist only in animals.
The H5N1 and H7N9 viruses are present mostly in Asia and the Middle East and have each affected over seven-hundred people. The current (and likely growing) numbers make these Type A avian flu ones that we should try to protect ourselves from.
Although the risk is limited, scientists do acknowledge that a mutation in either of these viruses could result in a pandemic (à la H1N1).(5)
What does it mean?
They found that the people’s immunity to those specific strains must have pre-existed, which means that they could not have been vaccinated against or infected by them.
This led the scientists to look more closely at what they call the “dividing year,” or 1968. This year marked the Hong Kong flu pandemic. By observing this particular time, the scientists were able to group different virus varieties together. They soon found that people born pre-1968 tended to be immune against H5N1, whereas ones born post-1968 tended to be immune against H7N9.(6)
Childhood Imprinting and its Benefits
Based on the finding listed above, Worobey and his team suggest that people born during certain years of flu outbreaks are less susceptible to infection. Scientists term this as “childhood imprinting” (which the study details further).
Worobey and his team have created models which suggest that childhood imprinting provides 75% protection against severe infection and 80% protection against death for both H5N1 and H7N9.
Ideally, these models will allow scientists to predict which age groups may be more at risk of infection should another influenza pandemic break out.(7)
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