At the start of the epidemic in China, the study found that the number of people infected doubled every 2.3 to 3.3 days, up from six to seven days before.
This means that the initial R₀ number, which is the number of people an infected person should infect, is also much higher. Most experts had this figure set at 2.2 to 2.7, but researchers believe it is closer to 5.7.
The findings were published in an article published by the Los Alamos National Laboratory and published Tuesday on the Centers for Disease Control and Prevention website.
The researchers said the results illustrate the need for active surveillance of confirmed cases and contact tracing, which means determining who they have been in contact with. Researchers are also advocating for early and strong quarantines and social distancing.
The higher level of infectivity also means that collective immunity will be more difficult to achieve. With a lower R₀, such as 2.2, only 55% of the population should be infected or vaccinated to obtain collective immunity. With an R₀ of 5.7, this number rises to 82%.
The many trips before the Lunar New Year were probably a major driver of the spread of COVID-19 in China
The study also hammers the path of the disease once a person is infected.
The researchers estimate that the incubation period, or the time it takes to experience symptoms after infection, is 4.2 days, which is consistent with other estimates.
The average time it takes before a person is hospitalized after experiencing symptoms varies considerably. Before human-to-human transmissions were reported in China, it took an average of 5.5 days for a person to be hospitalized. After January 18, that number dropped to 1.5 days.
The average time from hospital admission to discharge was 11.5 days and the average time to hospital before a person died from the disease was 11.2 days. The time from onset of symptoms to death was 16.1 days.
The researchers reviewed publicly available case data for confirmed COVID-19 cases and examined travel data from China. In particular, they examined data collected outside the epicenter of Wuhan disease in Hubei Province to avoid data problems caused by overwhelmed health care systems and changes in the way authorities reacted to the disease.
By the time COVID-19 reached other provinces beyond Hubei, authorities had access to diagnostic kits and were actively following the people of Wuhan.
At a briefing on Thursday, Canadian health officials estimated that before the introduction of tougher public health measures, each infected Canadian infected an average of 2.2 more people.
There are several reasons why China’s January figures could be higher. On the one hand, the study estimates that somewhere between 40,000 and 140,000 people in Wuhan traveled outside of Hubei Province before the isolation was imposed on January 23.
“The long journey before the Lunar New Year was probably an important driver of the spread of COVID-19 in China,” said the study.
Health officials in Canada also had the luxury of several months to prepare as they watched the epidemic spread around the world and implemented social distancing measures early on.
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