Before COVID-19, this term was often used when discussing the influenza virus because flu is among the fastest mutating viruses on the planet. As part of its evolutionary process, viruses mutate to try to escape the immune system. As the virus copies itself, its mix of genes can change slightly. This is called “antigenic” drift. Because the new virus is still mostly like the previous version, people usually have some immunity to a virus that has “drifted.” When the numbers of gene “drifts” start to pile up, the virus can become significantly different from its predecessor. This is called antigenic “shift.” When a virus “shifts,” humans have more vulnerability to becoming sick because their immune system doesn’t recognize it. Like the flu virus, the SARS-CoV-2 virus which causes COVID-19 has demonstrated an ability to mutate and escape vaccines.
Deeper dive
Drifts and shifts have resulted in new variants of the SARS-CoV-2 virus.
SARS-CoV-2 is a virus with a strand of 30,000 letters [which represent chemical properties] that make up its genome. To reproduce, the coronavirus, via a spike on its membrane, binds itself to the outside of a human cell and then enters it, hijacking the cell’s original genome, directing it to make copies of the virus instead.
Each time the SARS-CoV-2 virus reproduces, there is a natural possibility for a copying error in the letters, resulting in new variants of the virus. Much of the time, the copying errors are inconsequential or even weaken the ability of the virus to replicate. However, as most of the world has become infected with the virus, there has been the opportunity for an increased number of copying errors, resulting in mutated variants that make the pathogen more transmissible, more able to evade vaccines and potentially more lethal. In the summer of 2021, people became infected with the delta variant, then in the winter of 2021 and 2022, the omicron variant and in the spring and summer of 2022, people have been infected with variants of omicron. Each of these variants has caused a wave of illness, hospitalizations, and death.
The CDC has been monitoring these variants and classifies them in 4 ways, each representing and escalation in risk of causing waves of illness: variants being monitored, variants of interest, variants of concern and variants of consequence.