In July 2021, a Centers for Disease Control and Prevention presentation obtained by the press noted that the delta variant of COVID-19 “is as transmissible as chickenpox.”
As some researchers have pointed out, the CDC’s comparison was an overstatement. Based on various studies and projections, on average a person infected with the delta strain of COVID-19 can infect six or seven people, whereas someone infected with chickenpox can infect nine or 10. Nonetheless, both diseases are highly contagious, although the viruses that cause them are very different.
While many diseases, such as Ebola and influenza, originate from viruses that made relatively recent “jumps” from animals to humans, other disease-causing pathogens have been with humans throughout evolution. The virus that causes chickenpox is one of these, coexisting with the human evolutionary line for millions of years.
I am a microbiologist interested in pathogens and the diseases they cause . Chickenpox is a childhood disease, and until a couple of decades ago, nearly all children in the United States got it. A vaccine campaign that began in the 1990s has made the disease rare in children in the U.S., but the virus lingers in the body and can reappear in unvaccinated adults years later as shingles. The virus’s ability to do this disappearing-and-reappearing trick may be the key to its long evolutionary history.