A new study, which is of particular relevance to India, says mild, undocumented cases of coronavirus fuelled much of the early spread of the disease in China until containment measures like lockdown of cities and home isolation were put in place on January 23.
Undocumented cases amounted to more than 86 percent of all cases in the central Chinese city of Wuhan, the international study based on a simulated mathematical model said.
The findings indicate that a radical increase in the identification and isolation of currently undocumented infections would be needed to fully control the pandemic.
The study said that increased testing coupled with travel limits and limits on social contact could reduce the number of undocumented cases significantly.
It is clear that strictly maintained social distancing is key to containing the spread of covid-19 as it is almost impossible to detect all the cases – especially many cases are mild and show symptoms not different from the common cold.
Until those factors kick in, undocumented cases could be the super-spreaders of the coronavirus or the disease, covid-19.
“These undocumented infections often experience mild, limited or no symptoms and hence go unrecognised, and, depending on their contagiousness and numbers, can expose a far greater portion of the population to the virus than would otherwise occur,” said the study conducted by experts from China, the US, UK, and Hong Kong.
It was published online earlier this week by the journal, Science and included researchers from Imperial College, London and Tsinghua University in Beijing.
The undetected cases were 55 percent as infectious as the detected cases but because of the stealth nature of the infection – and higher numbers – they infected over 80 percent of the cases that were diagnosed, the study found.
The researchers tracked reports of infections in China from January 10 to 23, and then again from January 24 to February 8 and added that data to data available about population mobility during the Chinese New Year (CNY) into their computerised mathematical model.
“Overall, our findings indicate that a large proportion of covid-19 infections were undocumented prior to the implementation of travel restrictions and other heightened control measures in China on 23 January, and that a large proportion of the total force of infection was mediated through these undocumented infections,” the researchers said.
“This high proportion of undocumented infections, many of whom were likely not severely symptomatic, appears to have facilitated the rapid spread of the virus throughout China”.
Once the travel restrictions along with other factors like awareness and social distancing kicked in among the people, the percentage of undocumented cases decreased.
“The contagiousness of undocumented infections was substantially reduced, possibly reflecting that only very mild, less contagious infections remain undocumented or that individual protective behavior and contact precautions have proven effective”.
“Further, general population and government response efforts have increased the use of face masks, restricted travel, delayed school reopening and isolated suspected persons, all of which could additionally slow the spread of SARS-CoV2”.
The researchers said it was possible that this particular coronavirus could become endemic to the world.
“Our findings underscore the seriousness and pandemic potential of SARS-CoV2. The 2009 H1N1 pandemic influenza virus also caused many mild cases, quickly spread globally, and eventually became endemic. Presently, there are four, endemic, coronavirus strains currently circulating in human populations (229E, HKU1, NL63, OC43).”
“If the novel coronavirus follows the pattern of 2009 H1N1 pandemic influenza, it will also spread globally and become a fifth endemic coronavirus within the human population”
