The data are current as of 17 August 2021. You can also download a curated version of the data for this article from my Dropbox folder. I provided the link to the COVID-19 Spread Tracker from the Lin Lab at Harvard. Despite this limitation, the effective reproduction number may be useful to evaluate public health policy decisions to reduce the spread of the COVID-19 pandemic. But when I explored some of the work in this area, there appears to be a variety of methods for performing this technique. A technique called “nowcasting” is used to estimate the reproduction number. Reporting delays can impact the estimates for the effective reproduction number. There are some issues with the us of effective reproduction number for policy decisions. It seems to have worsened over time, but this could be due to poor data early in the pandemic. ![]() The effective reproduction number provides us with some interesting patterns in spread of COVID-19 by states/territories. and its states/territories (see example): For that, I direct your attention to the Lin’s Laboratory Group at Harvard, they have a great figure that shows the fluctuation of the effective reproduction number for the U.S. It doesn’t tell us much about how the effective reproduction number changes across time. One thing to mention is that this Cleveland plot only tells us one dimension of the effective reproduction number story (the difference between the most recent Rt and the earliest Rt). There may be data in between the two time periods that I could have used, but I left those out. Rather than fill these in, I left them empty. There were some missing data which are identified by a single dot (blue or red) or an empty field in the recent or past effective reproduction number. However, what is of concern is the high effective reproduction numbers in some states (Rt > 2), which indicates that the pandemic is still spreading at an alarming rate. This could be due to lack of good data in the early phases of the pandemic. It seems that some states have gotten worse in terms of increase effective reproduction number since the beginning of the pandemic. The blue dots denote the most recent effective reproduction number (14 August 2021) and the past dots denote the earliest effective reproduction number (17 April 2020). The Rt changes over time as the population susceptible to infection changes. Instead, the effective reproduction number (Rt) is used to provide a more realistic reproduction number based on the population being infected, recovered, or vaccinated. With the introduction of vaccines, the R0 isn’t a good measure of the reproductive capabilities of COVID-19. However, the underlying assumption with R0 is that everyone in the population is susceptible to infection. ![]() Figure 1 provides a visual explanation of the basic reproduction number. The reproduction number is the number of new cases that is directly caused by exposure to a single case. Reproduction number (R0) and effective reproduction number (Rt) However, one measure that is of great interest is the reproduction number or R0. Daily reports such as the John Hopkins COVID-19 dashboard provide end users with visual and statistical information about the surges in cases and deaths associated with COVID-19. Surveillance of COVID-19 remains an important public health measure of understanding the spread and impact. At the time of writing this article, there have been over 4.5 million deaths and over 216 million cases due to COVID-19. As the COVID-19 pandemic, which began in December 2019, continues into its second year, public health measures have been put into place to mitigate its spread.
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