The study found that 1,064 of the 1,568 sailors on board, or about 68 percent, had tested positive for the virus.
But the aircraft carrier returned to port while the outbreak was still underway, and the crew was quarantined, so it was not clear whether the virus ended up infecting new sailors, even after 68% contracted it.
In addition, outbreaks aboard ships are bad models for those on land because infections move much faster around a ship than in a civilian population at liberty, said Dr. Natalie E. Dean, a biostatistics at the University from Florida.
More importantly, Wuhan and Italy’s first estimates were later revised upwards, Lipsitch noted, once Chinese scientists realized they had counted the number of first wave victims less. It took about two months to make sure that there were many asymptomatic people who had also spread the virus.
It also became clearer later that “over-spreading events”, in which one person infects dozens or even hundreds of others, played a large role in the spread of Covid-19. Such events, in “normal” populations – where no one wears masks and everyone attends events like parties, basketball tournaments or Broadway shows – can raise the number of reproductions to 4, 5 or even 6, experts say. Consequently, these scenarios require greater herd immunity; for example, at an R0 of 5, more than four out of five people, or 80 percent, must be immune to slow the virus.
To complicate matters further, there is a growing consensus among scientists that the virus itself is becoming more transmissible. An “Italian strain” variant with the mutation known as D614G spread much faster than the original Wuhan variant. A recently identified mutation, sometimes called N501Y, which can make the virus even more infectious, has recently appeared in Britain, South Africa and elsewhere.