Antigenic Shift and Antigenic Drift: What could this mean for SARS-CoV-2?

Updated: Jan 19

By: Kylie Luo

Image Credit: Helyx Graphic Designer: Aidan Meyers

During this unprecedented time where SARS-CoV-2, or COVID-19, has taken the spotlight, scientists have begun to observe the patterns of previous pandemics in order to help combat the spread of disease and the COVID pandemic. By looking at these patterns, researchers can make predictions as to how today’s pandemic may behave in response to reopening the country and establish a tentative timeline as to when life may fully be restored to normal. One important factor to take note of when studying a virus is the fact that a virus can mutate, or change. This means that as time progresses, the form of COVID-19 can be shifted through processes called antigenic shift and drift, rendering certain vaccines ineffective.

Antigenic drift describes a genetic variation in a virus that causes its antibodies, or tags, to change, creating a new strain, or form, of the virus. Similarly, antigenic shift describes a similar phenomenon where two or more strains of different viruses combine to form a new virus. These happen through shifts in the proteins of the virus, which essentially changes their identity.

These two concepts of mutation can be applied to previous pandemics just as they can possibly be applied to today’s. In the early 20th century, a pandemic known as the Spanish Flu, caused by the H1N1 virus, rampaged the world, killing around 50 million people. Though during the time, no vaccine was invented to subdue the virus, the pandemic died down by itself and the disease seemingly disappeared. A few decades later, a new pandemic surfaced, later to be called the Pandemic of 1957. The virus affiliated with this outbreak was the H2N2 virus, which was believed to have mutated from the H1N1 virus through antigenic drift. Unlike the previous pandemic, a vaccine was quickly developed and administered, stopping the spread of the virus in its tracks. The last major pandemic of the 20th century was known as the Hong Kong Flu, which was discovered to be caused by the H3N2 virus. These pandemics occurred in such a short span of time, all with very similar viruses, making it a valuable resource to look at. The H3N2 virus, of which several strains still exist today, is looked at as nothing more than the yearly flu, which begs the question: Could COVID-19 turn into another annual shot?

COVID is proteolytic cleaved with 5 accessory proteins, which describes a virus’ ability and how prone it is to mutation. Given that Corona has 5 accessory proteins, there are many possibilities for it to shift or drift. Because of this, it is a very real possibility that the current pandemic could turn into an almost regular illness.

Although this seems very unsettling, given the state of uneasiness in the world surrounding the matter, it is important to remember that the Flu Pandemic of 1918 (H1N1 virus) was seen as the end of the world because so many people were dying. With modern knowledge and technology, vaccines for mutations of that very flu have become common and widespread, helping the safety of the community. If COVID-19 continues to mutate, technology similarly used to predict flu mutations can be applied, creating new vaccines for Corona, so that it is not as potent of a disease as it is currently.


Image Credit:

Helyx Graphic Designer: Aidan Meyers


What is the difference between antigenic shift and drift?

Antigenic drift happens when there are slight mutations in a virus that can accumulate. It can be thought of as substituting white sugar with brown sugar in a recipe, which would change the flavor profile of the final product. Antigenic shift happens when several subtypes of a virus come together to produce a completely new subtype that has traits of the original strains. For example, if you cannot choose between wanting a chocolate chip cookie or an oatmeal cookie, you compromise on a chocolate oatmeal cookie.

Why is the theory of the H1N1 mutating an important source to look at and compare to COVID-19?

During the 20th century, there were 3 major pandemics all caused by very similar viruses. Due to their similarity, it was theorized that the original virus, H1N1 of 1918 mutated into the other forms. This is important to consider when making a vaccine for any virus today, especially COVID, because they are very prone to change. By looking at patterns of the people the virus infected, and the times in between each outbreak, scientists can theorize the path that COVID-19 may take, allowing for better preparation for future circumstances.

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