Chancellor Angela Merkel appealed to Germans to stick to social-distancing rules to slow down the coronavirus pandemic after data suggested the disease was spreading faster again.

Germany is being closely watched worldwide as the most successful large European country in curbing the spread of the virus which has prompted a partial reopening of the economy. 

Merkel has frequently said the reproduction rate of the new coronavirus must be held below 1 to prevent the health system from being overwhelmed.

But the Robert Koch Institute for public health said the rate hovered above this critical threshold for the third consecutive day with an estimated value of 1.07 on May 11.

The latest number indicates that 100 infected people on average infect 107 others, meaning the number of new infections is accelerating again which could signal the beginning of a second wave of the pandemic in Europe’s largest economy.

The news report that reproduction rate had climbed back to 1.1 in Germany cast a shadow over the reopening of businesses from Paris hair salons to Shanghai Disneyland, and the easing of restrictions across the US.

What is virus reproduction rate? 

The reproduction rate, or RO (pronounced R-naught), of a virus is a measure of its transmission, or the number of new infections generated by each case. An RO rate of 1, for example, means on average each infected person will infect one other person they come in contact with.

What does the reproduction rate indicate?

A reproduction rate of less than 1 means that an outbreak is subsiding, since each infected person is transmitting the virus to fewer than one other person. An RO rate above 1 means the virus is spreading exponentially, with each contagious person infecting more than one other person. An RO of more than 1 is also an indication that hospitals and healthcare systems are vulnerable to becoming overwhelmed.

During the fast-spreading initial outbreak of the coronavirus in Wuhan, China, the reproduction rate was estimated at around 2.5, according to a World Health Organisation analysis.

Calculating the reproduction rate can be difficult, especially for a large country, with widely divergent demographic regions. A lack of capacity for widespread testing would also make it difficult to accurately assess the transmission rate.

What influences the coronavirus reproduction rate?

Population density is a major factor. The virus spreads much more efficiently in densely populated areas. Mitigation efforts, such as social distancing, school and business closures, and wearing of face masks all help drive the RO number down.

The characteristics of the virus itself is another major influence on its RO rate. This new coronavirus has demonstrated an ability to spread more easily than other viruses, such as influenza. 

It has a median incubation period of about five days, compared with two days for flu, and people with no symptoms of infection can spread the virus to others.

In addition, there has been evidence of transmission from close contact with an infected person even without virus particles spreading through coughing or sneezing.

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

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