What new waves of a pandemic might look like

During the First World War, the Chinese were, to put it mildly, not up to the rest of the world: there was a struggle for power in the country, the Chinese either declared war on Germany, then recognized this decision as unconstitutional, then announced it again. When the allies demanded help from them, the Chinese began to equip a kind of "construction battalion" for Europe. Chinese workers had to dig trenches, lay out telegraph wires, build barricades and railways.

In 1918, Paths of Infection: The First World War and the Origins of the 1918 Influenza Pandemic began in the country, an epidemic of "winter sickness" (today we would call it a "cold") - so it is not surprising that people with influenza found themselves among parts of the Chinese labor corps who went to war.

We know the result: World War I died from bullets and artillery in four years of war. Killed, wounded, and missing about 8.5 million soldiers, almost 13 million civilians became victims of hunger and murders. The number of victims of the "Spanish flu" taken out of China by unarmed workers reached 50 million in two years of the pandemic. Updating the Accounts: Global Mortality of the 1918-1920 "Spanish" Influenza Pandemic.

In 2016, Canadian historians reconstructed Reviewing the History of Pandemic Influenza: Understanding Patterns of Emergence and Transmission of the circumstances of the global pandemic. Although the picture was slightly different from country to country, there are three distinct waves of the pandemic around the world, occurring in the spring of 1918, the fall of 1918, and the winter of 1918-1919. Most of the victims of the pandemic died in the second wave.

Most of the Chinese went to Europe via Canada - they were dropped off at the port, put on trains, and then taken to the other side of the country and transported to New York. From there they were sent to Scotland, and then to France, where they finally found themselves in a war zone.

The Canadian Prime Minister quite reasonably feared that the Chinese workers would scatter on the way. To prevent this from happening, he assigned soldiers to the carriages. Here the first outbreak in 1918 happened: the Canadians blocked the route for the next Chinese units, but the disease had already burst out - the soldiers guarding the Chinese began to get sick.

One of the first "international hubs" of the disease was the British port city of Plymouth, a place where Chinese workers also traveled. From this port, along with the infected sailors, the Spaniard arrived in Europe, Africa, New Zealand and the United States. In four months, the disease spread to half the globe and began to kill.

The wave subsided in January 1919 - after the majority of people on the planet had been ill. People susceptible to the virus can be compared to "fuel": as soon as most of the fuel "burned out", the "machine" of the epidemic stalled. Therefore, the third wave was already more like a small flash. In the winter of 1918-1919, people without immunity to the Spanish flu became infected from time to time, but there were already few of them, so the third wave turned out to be much smaller than the second.

In 1918, there was a shortage of medical personnel in the rear. Reviewing the History of Pandemic Influenza: Understanding Patterns of Emergence and Transmission: Doctors and nurses were at war. Hospital places quickly ran out, so schools and other public places began to be adapted for hospitals. But even those doctors who stayed at home could do little to help the sick - vaccines and medicines for influenza had not yet been invented. Ordinary people were saved by the Great Pandemic: The United States in 1918-1919 with home remedies like a mixture of water, salt and kerosene. The demand for alcohol has sharply increased - many hoped for alcohol (even some doctors recommended drinking it to protect against the flu).

They didn't really know how to diagnose the flu. All the doctors knew was that the disease spreads with sneezing and coughing. Because of this, influenza was often confused with other diseases and was not properly recorded - so that outbreaks of the disease often went unreported. As a result, measures that could contain the spread of the disease were applied unevenly 1918 Pandemic (H1N1 virus) - or too late, when the optimal time to contain the disease was already missed.

Influenza-1918 and coronavirus-2019

The US Center for Infectious Disease Research and Policy (CIDRAP) believes that the best model for COVID-19: The CIDRAP Viewpoint for understanding the coronavirus pandemic is pandemic influenza rather than previous outbreaks of coronavirus disease.

The coronavirus disease COVID-19 associated with SARS-CoV-2 is not very similar to its other coronavirus predecessors. The SARS ‑ CoV ‑ 1 SARS epidemic of 2003 was quickly stopped, so that by 2004 there were no new cases of Severe acute respiratory syndrome (SARS), and MERS ‑ CoV, in principle, could not. Middle East Respiratory Syndrome (MERS) cause an international pandemic.

According to the researchers, the similarities between past influenza pandemics and the coronavirus disease pandemic are striking in several ways:

Population susceptibility … Both the SARS ‑ CoV ‑ 2 coronavirus and the influenza A (H1N1) virus are completely new viral pathogens to which humanity has no immunity. This means that any person who encounters each of these viruses is at risk of getting sick.
"Lifestyle" and method of distribution … Both viruses settle in the respiratory tract and are transmitted along with the smallest droplets of saliva.
Transmission by asymptomatic patients … Both viruses can be spread by people who do not even know they are sick.
Epidemic potential … Practice shows that both viruses are capable of infecting many people and quickly spreading around the world.

But there are also differences. COVID-19 is more infectious than influenza: reproduction index (R₀) Unraveling R0: Considerations for Public Health Applications in coronavirus infection above. It has a longer incubation period (five days versus two) and a higher percentage of asymptomatic carriers (up to 25 percent versus 16 for influenza). Moreover, the time of the greatest infectiousness, most likely, falls on the asymptomatic stage - in contrast to the flu, for which this moment occurs in the first two days after the onset of symptoms. Therefore, if influenza R₀ within 1, 4-1, 6 Modeling influenza epidemics and pandemics: insights into the future of swine flu (H1N1), then the coronavirus, according to various estimates, has R₀ can be from 2, 6 Report 9: Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand to 5, 7 High Contagiousness and Rapid Spread of Severe Acute Respiratory Syndrome Coronavirus 2.

So the Spanish flu pandemic of 1918-1920 and COVID-2019 can be compared with Report 9: Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand - and the comparison will be "in favor" of coronavirus disease. If we consider that at the peak of the Spanish flu, one patient infected Estimates of the reproduction number for seasonal, pandemic, and zoonotic influenza: a systematic review of the literature for two, then the hypothetical “tsunami” of COVID-2019 could be about one and a half to three times more dangerous.

Will there be a second wave

The outbreak of any infectious disease stops when its effective reproductive number, R_e, becomes less than one. This happens at a time when the number of people vulnerable to the virus decreases, so that the sick person can no longer infect anyone else.

To calculate how many people must become invulnerable for the pandemic to stop, the proportion of people (s) susceptible to infection must be taken into account. To stop the epidemic, sR₀ <1. That is, s <1 / R₀… And if R₀ coronavirus infection - 2, 6-5, 7, then that R_e in a specific case, it has become less than one, the proportion of people susceptible to infection should be less than 40–20 percent.

This can be achieved in the following ways:

If 60-80% of the population falls ill.
If the same 60-80% of people can be vaccinated.
If all infectious people are isolated from vulnerable people and their contacts controlled.

In this situation, the pandemic will stop and there will be no second wave. True, this will only work if the immunity of those who have been ill or vaccinated is stable A Perspective on Multiple Waves of Influenza Pandemics - otherwise, after some time, people begin to become infected in the second round. However, researchers do not yet know exactly how resistant the immunity to SARS ‑ CoV ‑ 2 will be. It should be borne in mind that, in principle, Coronavirus infections and immune responses of persistent immunity are not formed to coronavirus infections, so the risk of re-infection with another strain of coronavirus cannot be disregarded.

As in the days of the Spanish flu, humanity does not yet have any protection against coronavirus disease. There are no effective drugs - and they are unlikely to appear in the near future - and we will only be able to count on a vaccine in a year or two. However, we also cannot do nothing with the disease based on herd immunity - after all, then the coronavirus will kill 0, 9-7, 2% Coronavirus disease 2019 (COVID-19): Epidemiology, virology, clinical features, diagnosis, and prevention of patients, so the cost of immunity would be too high.

All that remains for humanity is to implement containment measures The effect of control strategies to reduce social mixing on the outcomes of the COVID-19 epidemic in Wuhan, China: a modeling study of the disease: either declare quarantine (as in China, Italy, Denmark and England), or call on the population to social distancing (similar to some US states and Russia). These measures can reduce the number of new infections and save thousands of lives - but they will not help to acquire an immune shield.

If we abandon social distancing prematurely, R_e will remain the same as it was. And since it is very difficult to understand when it is already possible to start abandoning measures to contain the disease, we have to admit that the chance of a second wave of COVID-19 is very high Beware of the second wave of COVID-19.

Lesson from St. Louis

There is little information about how they tried to contain the flu in Europe during the Spanish flu - almost no documents about this have been preserved due to the war. The war did not affect the territory of the United States, so there are more records in this country. Therefore, we know that in American cities and military bases, where we managed to introduce containment measures (quarantine, school closings, banning of public gatherings), mortality was lower than Nonpharmaceutical Influenza Mitigation Strategies, US Communities, 1918-1920 Pandemic, and the peak of the epidemic came later … True, in many communities, the directives of local governments about the dangers of influenza were poorly understood by Great Pandemic: The United States in 1918-1919, and were often ignored altogether.

For example, the Spanish flu arrived in St. Louis in October 1918. With the support of the mayor, the health commissioner, Dr. Max Starkloff, closed city schools, theaters, cinemas, entertainment venues, banned tram use and banned over twenty people from gathering. He even closed churches - for the first time in the history of the city. The archbishop was very unhappy, but could not reverse the doctor's decision.

In addition to measures that would today be called "social distancing", Dr. Starkloff worked with the population: he distributed a brochure among the townspeople, in which he called for covering your mouth with your hand when coughing so as not to spread the disease. The brochure was printed in eight languages - there was even a version in Russian and Hungarian.

Thanks to his efforts, the effective reproductive number (R_e) became less than one. However, St. Louis too early How some cities ‘flattened the curve’ during the 1918 flu pandemic relaxed. In the eleventh week of social distancing, the government decided that the danger was over and lifted the restrictions. People again threw themselves into schools and churches, and again they re-infected each other. As a result, R_e grew again - and the second wave of the disease began, more powerful than the first. Two weeks later, the government caught on and resumed restrictive measures, the epidemic began to decline, but, of course, there was no way to return the dead.

After the end of the pandemic, it became clear that even these "half-hearted" measures were beneficial. In St. Louis, 1,703 people died - half the number of neighboring Philadelphia. True, restrictive measures were also introduced in the city - but after the parade for 200,000 people was held.

What waves can be

In the twenties of the XX century, people knew very little about the nature of the Spanish flu - there was not even an exact certainty that it was viruses that caused it, and not the bacteria Reviewing the History of Pandemic Influenza: Understanding Patterns of Emergence and Transmission. Since then, humanity has accumulated knowledge and survived three more similar pandemics - and none of them was as devastating as the 1918-1920 pandemic.

We have not learned how to treat viral respiratory diseases, but we have learned to contain them. The effectiveness of deterrent measures can also be different - therefore, CIDRAP experts suggest COVID-19: The CIDRAP Viewpoint at least three scenarios, according to which the "second wave" could theoretically go.

Surf

How it might look. Following the first wave, the same waves will come once every 1-2 years, and starting from 2021 - slightly smaller waves.

Under what conditions? If everything continues to go the way it goes. In the end, states will have to loosen containment measures and people will have to go to work. Despite social distancing, over time, people begin to become infected again. When the pandemic reaches a certain threshold, the restrictions will have to be reintroduced - and the new pandemic will subside. Small waves will “roll over” humanity until 60-70% of people get sick - or until a vaccine appears.

Tsunami

How it might look. In the fall (or winter) of 2020, a "tsunami" will hit humanity, followed by several smaller waves in 2021 - as in the case of the Spanish flu.

Under what conditions? If the first wave of humanity does not teach anything. Instead of preparing for the second wave, the government will ignore the "warning" and will not spend money on staffing hospitals, and citizens will live as before: going to concerts, restaurants and other places where people gather. The situation will be similar to the "surf", only the next wave will immediately be gigantic - and quickly gain height. In this situation, 60–70% of those who have been ill, necessary for herd immunity, will be recruited quickly - but with great losses.

Ripple

How it might look. Like surf - but without having to re-introduce restrictive measures. That is, there will be no new pandemics, but there will be several minor epidemics in 2020-2021.

Under what conditions? If the SARS ‑ CoV ‑ 2 coronavirus quickly adapts to its new human hosts and therefore loses its lethal potential. This has not yet happened with influenza pandemics. But it is possible that it will be different with the coronavirus. SARS ‑ CoV ‑ 1 disappeared after the first epidemic - but it was much less contagious. In general, viruses of this family (for example, Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period, less dangerous HCoV ‑ OC43 and HCoV ‑ HKU1) tend to constantly circulate in the population and wait for the right moment to provoke another epidemic.