DEAR DR. ROACH: The newest COVID variant is reputed to be less deadly but highly contagious. What precisely makes one virus variant more contagious than another virus variant? Is it structure, size? — S.
ANSWER: It’s not size, because all coronaviruses are just about the same size. It is certainly the structure, but a virus has several adaptations that make it more likely to be passed from one person to another. When conditions include a highly persistent virus within a certain population, then, in general, those viruses that have mutations and enable better person-to-person transmission are more likely to be passed on.
Similarly, the strains of viruses that don’t kill their hosts (us) right away are more likely to be passed on, so we generally see more infectious — but not more deadly — virus variants, as infections stay around for years. Ideal conditions for a virus are lots of highly infectious viruses being produced for as long a period of time as possible, as well as times when people aren’t as sick that they don’t have to stay at home. Unfortunately, it isn’t always the case that viruses get less deadly over time. There is always a risk for a more contagious and more deadly virus.
The factors that make a virus more contagious are varied. Viruses that can reproduce faster and make more of themselves are favored. Those that contain lots of spike proteins, which attach to human cells and start the process of getting the virus into the cells, are also more likely to spread.
Getting around your body’s immune system (including the potential ability to infect someone who has had COVID before or who has been immunized) is another factor that predicts greater infectiousness.
Being up-to-date with the vaccine, using personal protection (especially masks) and staying away from crowds when risk is high remain the best ways of avoiding infection with SARS-CoV-2, the virus that causes COVID-19.
