Silent COVID-19 Infections Responsible For Early Spread: Study

Silent infections may have contributed to the rapid spread of COVID-19 at the dawn of the pandemic, a modeling study in China shows.

AsianScientist (Jul. 21, 2020) – Up to 87 percent of COVID-19 infections in Wuhan city may have gone undetected in the early days of the pandemic, according to a modeling study published in Nature.

These undetected, or unascertained, infections—which may include asymptomatic or presymptomatic individuals, or those with mild symptoms—are likely to have played a major role in the rapid spread of the disease, and could lead to a resurgence of infections upon lifting of restrictions too early.

To gain a better understanding of the proportion and effects of these undetected COVID-19 infections, Dr. Wang Chaolong and colleagues at the Huazhong University of Science and Technology collected data from 32,583 laboratory-confirmed cases in Wuhan from December 8, 2019 until March 8, 2020.

They used the data to study the transmission dynamics of the COVID-19 outbreak from January 1, 2020, and divided it into five time periods based on key events such as Chinese New Year and the imposition of centralized isolation and quarantine.

Their analysis reveals that the initial rate of transmission was very high, with an estimated reproduction number (R0) of 3.54 in the first period, falling to around 0.28 by the end of the study period. These results suggest that public health measures implemented between late January and March 2020 reduced the number of total infections in Wuhan by 96 percent by March 8, 2020.

By fitting their models to epidemiological data, the authors demonstrate that 87 percent of infections were undetected during the study period, with a lower bound of the estimate being 53 percent under an extreme assumption that all cases were detected at the initial phase.

Using the fitted model of these data, the authors go on to predict the chance of a second wave of infections. If all restrictions are lifted after 14 days from the first day on which no cases are reported, the chances of disease resurgence are expected to be very high (up to 97 percent). They also predict that the surge in cases would occur 34 days after restrictions were lifted.

Under a more stringent scenario in which all restrictions are lifted only after 14 consecutive days without cases, the probability of resurgence drops to 32 percent, and the surge could be delayed to 42 days after the lifting of restrictions.

These findings are consistent with recent serological studies in the United States and Europe, the authors say, adding that further studies are needed to confirm these estimates.

The article can be found at: Hao et al. (2020) Reconstruction of the Full Transmission Dynamics of COVID-19 in Wuhan.


Source: Nature; Photo: Macau Photo Agency/Unsplash.
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