The “second wave" really excites the minds in France since the beginning of the exit from self-isolation on May 11th. They also speak of an epidemic wave, that is, an epidemic that resembles a tsunami.
This is a monstrous wave that occurs due to an underwater volcanic eruption or an earthquake. In such cases, a second wave is often observed, which can be even worse than the first. The same phenomenon of the second wave applies to earthquakes on land: the second shock is worse than the first.
In the military sphere, there is the concept of a “second assault”, which also often plays a decisive role. Everything looks as if the first wave is preparing the second, decisive. This is observed in many phenomena, both natural and not.
In addition, epidemiology often speaks of a second or even third wave, describing successive epidemic phenomena among the population. Every year the first, second, and sometimes third waves of the seasonal flu are observed.
The concept of "consecutive waves" probably became popular after the flu pandemic of 1918-1919, which unfolded as part of three consecutive waves. Of course, it is not worth comparing Covid-19 with that terrible pandemic, but conclusions can be drawn in order to better understand the current situation.
This historical pandemic did not originate in Spain, but (again) in Asia. The H1N1 virus that caused it became a combination of human and avian strains. It claimed at least 20 million lives around the world, probably twice as many. This pandemic had three phases.
The first phase or wave was not too serious and unfolded from April to August 1918. Moreover, it was very contagious and covered more than 50% of the military. But given the low severity of the disease and wartime conditions, French newspapers practically did not write about it: they said that nothing serious happened, it was just flu.
But at the end of May 1918, Spain was already seriously affected by the epidemic, especially the Madrid region, and its economy experienced a significant recession. It was then that the concept of "Spanish flu" arose, which is not true, since Spain was its source no more than any other European country (in Spain, the virus was most talked about, although other European countries suffered no less, hardly mentioned it).
In July 1918, the epidemic seemed to begin to subside, but the course of the disease became more and more difficult (very serious and even fatal complications to the lungs were increasingly occurring). Nevertheless, in France, few people cared because everyone believed that the French were strong enough to cope with the epidemic.
At the end of August 1918, the epidemic again gained strength, and very significantly, starting in the south-west and west of France.
Thus, in September 1918, the second wave of flu started, which became a very serious blow. First of all, this concerned young people (20-30 years old), in whom only a few days later pneumonia quickly became fatal: a lot of people died from it. A second and much more terrible epidemic wave quickly swept Africa and Latin America.
This time all the French newspapers wrote only about the flu. The hospitals were crowded. They advised to isolate patients, to wear a mask, to avoid public meetings and enclosed spaces, where many people gather at once.
In late October - early November 1918, the epidemic slowed down. At the beginning of December 1918, a slight increase was noted, followed by a further decline.
Nevertheless, in February-March 1919, the third, no less serious wave of the epidemic began. All continents were covered, and the toll reached 6 million dead in India alone. Clinically, an unusual symptom was observed: hair loss. Then the disastrous pandemic nevertheless came to naught, leaving behind tens of millions of deaths, especially among young people.
To understand whether the risk of the second wave is real, it is important to recall the 1918-1919 flu pandemic, which has left a deep mark in the minds due to high mortality, especially among young people.
Its distribution in three waves was also struck into the memory of epidemiologists, some of whom tend to shift it to other epidemics. Nevertheless, influenza is a very unusual virus: it is an RNA-containing virus, like coronaviruses, but it has one significant difference.
The genome of the influenza virus is segmented, that is, it includes eight different components. It is not resistant, can easily and often change. Every year its genome undergoes minor changes, but from time to time there are big changes, genetic breaks that cause pandemics (because the result is a "new virus" from which people have practically no immunity).
When the pandemic began in April 1918, the virus was very contagious, but not particularly dangerous. Nevertheless, the pandemic picture changed dramatically in July-August 1918.
Of course, at that moment we did not have any biological means to understand what was happening with the virus, but scientists believe that in the summer of 1918 there was a serious mutation, a genetic gap. The population did not have antibodies against the new virus, and therefore, the immune system could not fight it. Older people could already deal with a similar strain in the past, but the immunity of the younger generation did not have such experience. This explains a large number of victims of the second and third waves among young people.
It is also important to take into account the knowledge about the SARS-CoV-2 coronavirus, which, like all coronaviruses, generally does not differ in segmented RNA. Their genome is quite stable and even has a system for correcting errors in cell replication. Moreover, it can evolve, since it has certain plasticity.
It is worth noting that several small mutations have occurred since the onset of the Covid-19 pandemic, and three different strains currently exist. But these mutations have nothing to do with the periodically occurring genetic breakdowns of the influenza A virus, as it was in the summer of 1918. For this reason, fears of a disastrous second wave, as was the case with the 1918 flu pandemic, seem unjustified.
In addition, scientists believe that a significant part of the population is immune to Covid-19, which arose even before the outbreak due to its proximity to coronaviruses that cause rhinitis, rhinopharyngitis, and a number of acute viral gastroenteritis.
Today it is believed that immunity from Covid-19 pertly exists. Nevertheless, due to the lack of mass testing of the population, it is impossible to say how many people were infected with the virus without the manifestation of serious symptoms and signs (in such cases, the person feels only a slight malaise). If there are many such people, and they have formed immunity, this should contribute to the emergence of collective immunity, which should prevent the second wave.
Collective immunity is a determining factor in the occurrence of the second wave. It is possible to say that in France, self-isolation measures were poorly enforced, and the virus continued to spread. The slow spread of the virus, of course, contributed to the strengthening of collective immunity.
I can say that the risk of the second wave is real, but there are more arguments against it than for it.
Epidemics succeed each other but do not resemble each other. The Covid-19 epidemic has little in common with the epidemic of plague, cholera, typhoid, smallpox, polio, meningitis. Despite all the gaps in this approach, Covid-19 is closest to influenza.
The influenza pandemic of 1918-1919 claimed many lives, but ended in April-May 1919, although at that time there was no vaccine, no effective antiviral drug, no antibiotic (against a secondary bacterial infection).
Hygiene was only just beginning to develop, and medicine was not very effective. In addition, World War I led to the deaths and impoverishment of the population. But even in such adverse conditions, the pandemic ceased, and without the use of any special methods.
By reading archival data on this pandemic of the early twentieth century, you realize that people's reactions and behavior have not changed too much. Surprisingly, many of the mistakes of those times were repeated today.
In other words, conclusions can be drawn from past epidemics, but for this, you need to make real efforts, which do not always happen since the experience of ancestors does not serve as a guide for many people. But whatever these findings may be, the control plan needs to be adapted to each epidemic. That is, only a vaccine can be a real solution.