Explainer: Tracking the coronavirus ‘reproduction rate’ as lockdowns ease

(Reuters) – A global alarm against a possible second wave of coronavirus infections was triggered on Monday after Germany reported that the pathogen's reproductive rate had risen above 1, indicating that the disease was only a few days after the first preliminary steps to reopen the pathogen's re-expanding economy.

A man wears a protective face mask as he walks past closed shops during the Coronavirus Disease (COVID-19) outbreak in Manhattan, New York, the United States, May 11, 2020. REUTERS / Mike Segar

The following explains what the virus replication rate is and why it is important to understand the impact of ending economic barriers to curb the spread.

WHAT IS A VIRUS REPRODUCTION RATE?

The reproductive rate or RO (pronounced R-nothing) of a virus is a measure of its transmission or the number of new infections newly generated. For example, an RO rate of 1 means that, on average, every infected person infects another person they come into contact with.

WHAT DOES THE REPRODUCTION RATE INDICATE?

A reproductive rate of less than 1 means that an outbreak will subside, as each infected person will transmit the virus to less than another person.

An RO rate above 1 means that the virus spreads exponentially and infects more people than any other person. An RO of more than 1 is also an indication that hospitals and health systems are susceptible to overload.

During the rapidly spreading first outbreak of coronavirus in Wuhan, China, the rate of reproduction was estimated to be around 2.5, according to a World Health Organization analysis.

HOW EASY TO CALCULATE THE REPRODUCTION RATE?

Reproduction rate calculation can be difficult, especially for a large country like the United States with very different demographic regions.

“In rural Montana, the R-zero could be less than one. In urban areas … it could be R1 or maybe a little bit more than that, "said Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center in Nashville.

A lack of capacity for extensive testing would also make it difficult to accurately evaluate the transfer rate.

WHAT INFLUENCES THE CORONAVIRUS REPRODUCTION RATE?

Population density is an important factor. The virus spreads much more efficiently in densely populated areas. Mitigation measures such as social distancing, the closure of schools and companies and the wearing of face masks help to reduce the RO number.

The properties of the virus itself are another important influence on its RO rate. This new corona virus has been shown to spread more easily than other viruses such as influenza. It has an average incubation period of about 5 days compared to 2 days for flu, and people with no symptoms of infection can spread the virus to others. In addition, there was evidence of transmission through close contact with an infected person, even without virus particles spreading through coughing or sneezing.

The level of immunity in a population, either due to previous infection with a virus or due to vaccination rates, also affects RO. In this case, there is no approved vaccine and no one had immunity when the virus first appeared.

DO WE HAVE TO CARE IF THE REPRODUCTION RATE RISES?

The short answer is "yes". This could be an indication of a new wave of infections.

The news that the reproductive rate in Germany had dropped to 1.1, which was seen as the success story of coronavirus abatement, cast a shadow over the reopening of shops on Monday from Paris hairdressing salons to Shanghai Disneyland and the relaxation of restrictions across Germany States.

While the political decision to reopen the state and local economy in the United States has already been made, caution should be exercised, Schaffner said.

"If you open up too quickly, medical problems will suddenly increase," he said. "It's a delicate balancing act. We shouldn't go too fast. "

Reporting by Deena Beasley; Edited by Bill Berkrot

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