The second wave of coronavirus: how to recognize it and what country it has faced

In Israel, Germany and other countries partially return quarantine measures. This is the second wave of the pandemic? Explains “Medusa”.

Вторая волна коронавируса: как ее распознать и какие страны с ней уже столкнулись

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In the United States on 27 June recorded the highest number of confirmed cases of coronavirus infections — a day ill 45 thousand people. In Germany in the outbreak at the meat processing plant restrictions imposed for 600 thousand people and 7 thousand was put on quarantine. In Israel, where until June of the case seems to be going well, last week tightened the rules of wearing medical masks. It seems that all the signs of a second wave of the pandemic, about which so much is said. In reality, the situation is more complicated: in some countries, there is no second wave is not yet visible, and in others one can see not only the second but also the third wave. The universal reasons why this is so, no — it seems that the situation is always different and much depends not on the officially announced measures to fight the epidemic, and from the behavior of people.

In the latest issue of popular science podcast The Shortwave devoted to coronavirus infection in the United States, the presenters started a conversation like this: “hi! We have an important message — the second wave does not exist. Just because the first wave [in the US] were not even close to over. Thank you all, you were Maddie and Emily, goodbye.”

It really reflects the current situation in America: the number of daily reported cases in the country in mid-April (on the “first peak”) was, on the average about 30 thousand, about the same number of infections recorded in the last two weeks. While below 18 thousands of infections every day, the rate of infection in the USA has never with APR did not fall.

If you try to dig deeper and take matters on different areas in the United States alone (in the graphics easy to see here), among the different States can be found as examples of very simple, monotonic growth cases (CA) and cases where there really seems to be visible to the second (Alaska, Montana), or even third or fourth (West Virginia) wave cases. But before you find out the real waves or not, and to determine their order, we must still deal with what should be considered as a wave.

What is the second wave?

The second wave — a concept that has come from epidemiological modelling. When working with models of the wave of new infections arise as a result of clear changes in the settings of the model — for example, when removing or resumption of quarantine measures that change the basic reproductive number R₀ and, thus, the speed of propagation of the disease. Such changes lead to the expected bursts that can be easily measured and numbered.

However, it is important to understand that the reasons for changes in the real statistics in a real epidemic, scientists always have to just guess. In this case, it is not clear what should be considered as this second wave. Daily and even weekly statistics on the recorded cases, and the setting is very “noisy”, subject to many accidents, and if you look only at him, then at desire it is possible to detect dozens of different “micro-wave”. Therefore, before seriously talking about the second wave, you must first agree on the principles of averaging the data — that is, what period is considered enough (but not too) large, and how significant spike in cases of infection can be considered a full-fledged second wave, and what better attributed to chance.

As a simple conservative approach to averaging it is possible to stop that just take data every two weeks. This is convenient because during this period the majority of cases end in recovery or death.

If you take this approach to averaging, the first burst in each country can be considered the two-week period, after which the decline in the number of registered cases. The lowest point, or “bottom” of the epidemic — the moment when the number of cases over two weeks again began to grow. Fortunately, while in most countries the decline continues, so that the “bottom” they have not reached, but there are some important exceptions.

Agreeing on this approach, it is possible to calculate the relationship between the number of cases registered in the last two weeks, so their number, which was recorded at the “bottom” of the epidemic. The resulting ratio it is possible to calculate for all countries, where growth has resumed, and it will reflect (albeit very roughly) how much the situation has deteriorated compared to most calm in the epidemiological period.

Technically we have been living on the crest of the second wave. This is due to the fact that the original outbreak in China was relatively quickly suppressed, before there has been a considerable growth beyond. The average number of reported cases at the end of February was not more than three thousand people a day, and compared with this current level of 150 thousand a day, of course, you can call this “second wave”. This serves as a reminder that the epidemic could be relatively easily prevented, if the action against her was taken by countries strongly and ahead of developments.

Which countries are already faced with the second wave?

If you look at the different countries separately, we can identify several such, which really has already begun the secondary growth of morbidity after a relative lull.

Israel

The most striking example. In mid-may in Israel, recorded an average of about 17 cases a day, and over the past two weeks is the average value increased more than 20 times and has a tendency to increase (25 June, for example, was 532 cases). Authorities have already begun to respond to such an unexpected secondary growth: Monday, June 22, Prime Minister Benjamin Netanyahu made a statement about the need to increase distancing between people, announced a fine of 500 shekels (about $ 145) for being in public without a mask, and predicted that many areas will again be included in the list of those which restricted movement.

Morocco

Here the situation is developing in a similar way. In April in Morocco too saw a significant surge in the incidence, which in early June was followed by a lull. Over the past two weeks in the country again recorded approximately 300 cases in a day, despite the fact that the test level is constantly increasing, and the proportion of positive tests of the total test only falls.

China

In the countries with strongly deteriorating situation in present China, where recently registered daily only two or three dozen patients. It may look strange, but actually quite expected and due to the fact that the secondary peak in this country started from a very low base. Prior to the resumption of flights and the beginning of a reverse import of infection from abroad, here (in may) was observed only isolated cases of the disease. Against this background, the increase to 20-30 cases a day, of course, looks are significant.

Australia and South Korea

Considerably more modest in scale, but similar in dynamics to look and data of Australia and South Korea — and here and there the current number of cases is not comparable to what was observed for the first peak, and getting into the world’s top growth incidence due to the almost complete elimination of domestic transmission in the most favorable period after the peak.

Panama, Philippines, Sweden

Quite a different situation exists, for example, in Panama, the Philippines and Sweden. There is a second peak was significantly (at times) — much higher “spread” first, not only the dynamics but also the absolute value of the number of cases is not encouraging. We can confidently say that there is a high secondary growth is not exactly related to the low base. But is there such a growth in some other common explanation is not clear: these countries are too different. The only thing that unites them — a very high proportion of positive results among all tests. This may indicate that the test here is insufficient: the more tests, the more the patients revealed, but the proportion of positive tests is lowered. So we really don’t know how well published the statistics reflect the real situation and is it fair at all to say about the second wave.

Why is there a second wave?

It is natural to assume that the emergence of the second wave is due to the fact that in countries where it is fixed, the government is too early took quarantine measures. In favor of this version says the example of Israel in the middle of may there began to work in kindergartens, then opened the beaches and the resumed work of public transport. A few weeks after this began the growth of cases and the daily number of new cases been in the hundreds (28 Jun ill 621 people). Advising the government experts believe that after a few weeks it may reach several thousand per day.

But to confirm this hypothesis, based on objective data from different countries does not work: people behave in them is too different.

It should be emphasized that we are talking about the formal rigor of measures that impose of the government, not about the real level of compliance. About the latest can be seen indirectly via another parameter is the mobility of residents, which is reflected in the data of mobile operators or navigation services. But there are differences in the development of the situation in the different countries are too significant to be able to draw any General conclusions about why in some countries, the second wave appears, but not in others.

For example, if we compare the similar dynamics of the epidemic, Israel and Morocco, we see that not only formal rigor, but also in real mobility quarantine in Morocco was significantly more stringent than in Israel — but it didn’t help prevent new outbreak, even at a fairly high level of testing.

On the other hand, if we compare the mobility of people in Germany and Russia, we can see that they are very similar — both in the depth of the fall activity, and the duration of the recession (the only difference is that in Germany the decline started earlier). The results of such similar “quarantine” was very different: Germany is now increasingly talking about the “second peak”, which in some districts is again tightened quarantine measures (in connection with the outbreak at the meat processing plant of the company Tönnies). But this “second peak” an order of magnitude (15 times, when compared by two-week periods) less than “recession”, which is observed today in Russia.

Why the second wave does not occur everywhere?

Fashion to talk about the multiple waves of the epidemic are largely asked themselves epidemiologists. And now they have to explain why in some countries, secondary outbreaks occur, and in others it seems to be there, although imposed restrictive measures look very similar.

One of the most famous works, where was predicted a significant increase in cases, — report of the group Neil Ferguson of Imperial College in London on the consequences of the uncontrolled spread of infection in the UK. Such bursts are expected in other, more primitive models, and in all cases they are based on the simple fact that without education, herd immunity (a significant number of ill or vaccinated in the population) the lifting of quarantine measures inevitably leads to the fact that the increased incidence with nothing held back.

But the model of Ferguson (one of the most detailed at the time of its publication), and later theoretical epidemic model did not account for everything. Including such important, as it is now becoming clear that the factors as the heterogeneity of the society and changed with the beginning of the epidemic behavior of people.

Heterogeneity

The speed of propagation COVID-19, apparently, is not the same among people of different classes and different social groups. It turned out to be very important to consider when predicting: some of the media, according to the latest data, can be responsible for a much larger share of infections than you would expect. So, those average estimates of the speed of propagation of the coronavirus, which is based on the results of their “work” may be overstated relative to real — just due to the fact that in the first phase the spread of the coronavirus provided just active “superspreader”.

The behavior of people

That predict response to an unprecedented pandemic is very difficult, frankly admitted himself and Ferguson with colleagues. And in this forecast, scientists have stipulated that the future effectiveness of the introduction of quarantine measures will depend heavily on how they react to people. But to consider in advance the reaction was impossible due to the fact that examples of these large-scale epidemics in the recent past was not simple.

Then the researchers were concerned primarily that no one is as they expected, will not abide by quarantine for as long as required. However, it is possible, in practice, it was not out of visiting public places and socializing with people and change habits. So far none of the models do not take into account the effect of the universal wearing of masks and gloves, the rule of distance when communicating and other small, simple but very mass measures. Maybe they explain the discrepancy between the real current situation in wealthy countries gloomy scenarios, which only recently was expected by epidemiologists.

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