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When and what would be the second wave of the corona virus

June 17, 2020

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This story originally appeared in The Conversation

When and what would be the second wave of the corona virusWhen and what would be the second wave of the corona virus

By Adam Kleczkowski, Professor of Mathematics and Statistics, Strathclyde University

As the new corona virus spread rapidly in February and March 2020, many governments introduced strict blocking measures. Thanks to massive public efforts, these countries have managed to stop the pandemic.

Countries like Slovenia and New Zealand have combined different approaches to public health and eradicated the virus within their borders. Other countries, including the UK, have made significant progress in containing the spread of the disease. However, the blockade has led to significant economic and social losses in countries where strict social distancing measures have been applied. Both governments and the public are now trying to lift restrictions and return to normal life.

With the relaxation of the blocking rules, warnings of a possible recurrence of COVID-19 cases, the so-called second wave, are issued. The second wave of the Spanish influenza pandemic of 1918-20 was particularly devastating, as was the second wave of the H1N1 influenza epidemic in 2009-10. So what can be done to avoid a second wave of COVID-19?

The second wave of the 1918 flu pandemic.

The second wave of the 1918 flu pandemic / Image: The conversation

In order for the virus to spread, it must be supplied with infected and susceptible hosts and successfully transmitted. These factors are conveniently captured by the number of reproductions, R, the average number of new cases caused by an infected person. A value of R greater than one means that the number of cases increases as they decrease below one. Before closing, the coronavirus R value was estimated to be two to four.

Countries such as China, South Korea, New Zealand, the United Kingdom and most European countries have now reduced this value to less than one. In other countries such as Sweden or Russia, the value of R remains close to or above one, reflecting the increase in the number of cases.

The relationship between population behavior and the value of R is complicated, but we can still use this concept to illustrate what the second wave might look like.

What a single wave epidemic looks like.

What a single-wave epidemic looks like / Picture: The conversation / Adam Kleczkowski

As long as there are vulnerable and infected people in the population, the virus can spread. There is evidence that the first wave of the epidemic resulted in restricted immunity that was well below the pack’s immunity level. There are also population groups in which the virus not only survives, but spreads further. Transfer to nursing homes is now a large percentage of cases in many countries.

When the closure measures relax, people start to interact more with each other. This could lead to an increase in the values ​​of R. However, it is important that the value of R be kept below or equal to one, as shown in the following figure.

Another example of a single wave epidemic.

Another example of a single wave epidemic / picture: The conversation / Adam Kleczkowski

But even a relatively modest change from R to 1.2 would lead to a big breakout that would trigger the second wave, which shows how important it is to apply control measures properly.

What could seem like a second wave.

What might seem like a second wave / Image: The conversation / Adam Kleczkowski

The response to the second wave requires recurrent blocking measures, as shown below. Although society has followed the restrictions remarkably well so far, the tiredness of the blockade could make it more difficult to reintroduce such strict guidelines.

Repeated outbreaks.

Repeated eruptions / picture: The conversation / Adam Kleczkowski

The epidemic could persist through fall and winter if seasonal flu could be common. Although it appears that the SARS-CoV-2 virus is not greatly affected by the weather, the health care system could be overwhelmed if COVID-19 and the flu attack at the same time.

On a positive note, preventive measures against the SARS-CoV-2 virus (such as face masks and hand washing) could reduce the spread of the flu virus.

Eventually, the virus could mutate into a more infectious strain. Such a mutation could have made the second half wave of the Spanish flu particularly severe. If something similar happened to the SARS-CoV-2 virus, the resulting epidemic would dwarf the current outbreak, even if the new R-value was only four, compared to 10-12 for mumps or 12-18 for measles . Mumps and measles can only be avoided by vaccination.

A large fall wave caused by a potentially mutated virus.

A big autumn wave caused by a possibly mutated virus / Image: The Conversation / Adam Kleczkowski

This article is republished by The Conversation under a Creative Commons license. Read the original article.