How second wave of COVID-19 is going to be?

COVID-19 was identified 10 months ago at the end of 2019. Since then, it has gone through different phases of acceptance and health alarm that ended with the preventive closure of all activities in many countries. Thanks to this drastic measure, it was possible to reduce the rate of spread of the unknown virus in many regions around the world. After this time and almost a million official deaths (at the end of September 2020), many analysts conclude that the first wave of the disease is over. This stage has served to learn many things about the virus and how it attacks humans. However, we are still largely unaware of what will happen next. Most countries are beginning to unleash their citizens. The country's economy is often one of the main reasons for relaxing the quarantine measures. Under these circumstances and without fully effective drugs or a vaccine against COVID-19, it is very likely that the number of infected will increase again. This rebound on the infected chart is what analysts call the second wave.


Estimated repeated outbreaks (Adam Kleczkowski)

Right now, different scenarios are being considered for how this wave of contagion, illness and death will occur. To create these hypotheses, the findings made during this almost first year of COVID-19 have been fundamental, but data from how the influenza pandemics of the early, mid-20th century and the early 21st century have also been used. To this, must be added all the prior knowledge of how the contagion of other coronaviruses such as SARS-1 or MERS works, also compiled at the beginning of the 21st century. While COVID-19 may follow a path other than these, there are three possibilities that are believed to be the most likely to predict the development of the disease.

The first case would be the most similar to the process that flu pandemics have followed. The disease would become seasonal, increasing the number of cases during winter and decreasing with the arrival of good temperatures. The cases of infected would increase in each winter and would moderate during the summer until a way is found to contain the disease. However, the data recorded during the spring and summer months of 2020 seem to indicate that there has been no decrease in cases during this period. Which would suggest that the real big wave of infections is actually yet to come during the following winter. If this hypothesis were fulfilled, without a doubt, it would be necessary to return to population confinement. The strength of this hypothesis is that it is how the last great pandemics of humanity have worked, including the Black Death. On the other hand, the coronavirus does not seem to have this type of behavior associated with environmental changes.

The second most plausible scenario would involve a second wave of similar magnitude to the first. This second would be followed by a third and a fourth with similar characteristics until in early or mid-2022 the disease itself would descend into isolated cases and would stop behaving like a pandemic. This scenario unrelated to environmental conditions is the most consistent with the data we have on SARS-1 or MERS. This is always based on data on acquired immunity and herd immunity from the other coronaviruses. As of today, we do not know the ability to maintain immunity against COVID-19 in humans, and ,although anecdotal, cases of people who have been infected more than once during the pandemic have already been reported. To this, must be added that neither of the other two diseases reached the magnitude of the present coronavirus.

The third hypothesis of the development of the COVID-19 pandemic assumes that the worst is over. Although there would not be a new wave with a high number of infections in a short time, it does presuppose that there would be a constant trickle of new cases. In these circumstances we could not speak of a clear transmission pattern. Also, this scenario would be expected if the containment measures could be maintained indefinitely. In the event that we reached this scenario, perhaps the security measures would be relaxed and we could reach one of the other possible scenarios. Unfortunately this pattern has never been observed in the pandemics that have ravaged humanity. Normally when a disease strikes with the magnitude with which the coronavirus has done it, the pattern of infections is not expected to drop drastically, at least not without an effective way to stop the virus.

Finally, it is possible that the virus behaves in different ways in distant regions. For example, environmental changes may not be enough to create seasonality in one geographic area but in another or that certain human populations have a greater natural resistance to disease than others. In any case, it is clear that the containment measures that have be proved useful in this and other pandemics seem the best defense that humanity has to stop the number increasing of infected.

Biblio:
Anderson RM, Heesterbeek H, Klinkenberg D, et al. How will country-based mitigation measures influence the course of the COVID-19 epidemic? Lancet. 2020 Mar 21;395(10228):931-4
Gulland, A. 'The pandemic is not over': WHO chief urges Europe to brace for second wave. The Telegraph. 2020 May 14. https://www.telegraph.co.uk/global-health/science-and-disease/pandemic-not-chief-urges-europe-brace-second-wave/
He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med 2020 (published online Apr 15)
Li R, Pei S, Chen B, et al. Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2) Science 2020 (published online Mar 16)
Moore KA, Lipsitch M, Barry JM, Osterholm MT, COVID-19: The CIDRAP Viewpoint Part 1: The Future of the COVID-19 Pandemic: Lessons Learned from Pandemic Influenza. CIDRAP, University of Minnesota. 2020  April 30.
Murray CJ, Lopez AD, Chin B, et al. Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918-20 pandemic: a quantitative analysis. Lancet 2006 Dec 23;368(9554):2211-8
Viboud C, Simonsen L, Fuentes R, et al. Global mortality impact of the 1957–1959 influenza pandemic. J Infect Dis 2016 Mar 1;213(5):738-45
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