I wonder why this happened, what may be behind the phenomenon?

The answer could be arranged by saying that these respiratory viruses are just like that: they do not spread very much in summer and spread in autumn / winter. In order to make a realistic risk assessment, it was necessary to assess the degree of seasonality, its timing, and whether there are other reasons behind the current acceleration. By the end of the third wave, it could already be seen that the seasonal effects had also entered the rapid decay, and we also estimated the extent of this from the model. In the summer, there are already scenarios that if he works the same season change and then works against us, combined with the release of defenses and the more contagious delta variant, the fourth wave could bring a steeply rising uphill curve if inoculation is not effective. What was more surprising about this was how slow growth was after school opening, and even the pace of spread even slowed down a bit in mid-September. So the question is more:

why has this sudden change just happened?

This is not only happening in Hungary

It is worth noting that the October acceleration is not typical for Hungary: a similar trend reversal took place in Central Europe at the same time, should therefore also be a factor specific to the whole region. The extent of the turnaround, of course, varies from country to country, as these countries are characterized by different trans-infestations as a result of previous waves, and different instruments are in place. Their level of vaccination also varies, but typically lags behind the EU average (with the exception of the Germans, but there are also regional differences).

Below, we’ll take a look at the reasons that could potentially accelerate into an epidemic, and see which of these might come into play.

Possible reasons are that we are seeing a rapid increase in the number of cases

• Relaxation of measures – NO

During the pandemic, we observed on several occasions in different countries that its measures were limited as the spread accelerated. Recently, however, this has not happened.

• The number of contacts has increased – UNlikely

The number of contacts may vary independently of the central measures. During the European Football Championship in the UK, young people rushing into pubs produced a strange epidemic curve that joked even the best British modelers. The number of contacts is also monitored in Hungary, both with an online questionnaire, both with representative surveys. The number of contacts increased from April to the end of the summer, but not much since then, and the mobility indices have not jumped recently. However, these surveys are not really suitable for assessing the impact of individual mass events. If the increase in contacts were the main explanation, it would have to be in sync with the other countries involved.

• The reported data exaggerate the severity of the epidemic – NO

Data reliability was a sensitive issue throughout the pandemic. It has been the case that certain data sets are false images of the true evolution of the epidemic, but even then they have typically underestimated the severity of the situation. At present, however, several indicators from independent sources point in a similar direction: the situation is deteriorating in both respects.

• We’re testing more – NO

At the beginning of the second wave, it was a popular misconception for a while that the number of infected people didn’t even increase, we just tested more so we find more cases. This has been refuted by the increase in the positivity rate of the tests then and now, which indicates that the correlation is just the opposite: as the number of patients increases, so will the number of tests performed. The active test positivity rate indicates that the reported case numbers tend to underestimate the true growth rate. ready the workload of hospitals is also increasing dynamically, which is independent of testing activity.

• Decreased level of individual defense – NO

It could lead to a sudden increase in the number of cases if many people gave up individual defense at once. In recent weeks, however, we have seen a loss of this, with more and more institutions reintroducing mask use. According to him, the willingness to wear a mask has increased in recent weeks, although our surveys are still below the required level

• Spread of a new variant – NO SUCH DATA

The rise of the alpha variant caused an increase in the measured number of reproductions in January-February. Semi-grafted Eastern Europe, where it is even extensive, is a favorable terrain for a variant that can evade previously acquired immunity. Another spread may also cause the current phenomenon, but we do not currently have such information. It should be added, however, that countries are not at the forefront of variant monitoring, so it is questionable whether a region would be able to detect a new variant emerging in our neighborhood.

• External effects – POSSIBLE

The epidemic situation in the low-vaccinated Balkan countries is very serious and they are strongly linked to the Central European region through mobility. It is conceivable that a significant number of introductions also play a role in the onset of the epidemic, although with a well-functioning epidemiological system, imports do not cause a nationwide epidemic. There has been a strong upswing in the south-east of Hungary, and Germany is now deteriorating in the southern and eastern regions. state. The severe epidemic in the Baltic states is also linked to the fact that the virus is not under control in Russia either.

• Seasonality, environmental factors – POSSIBLE

Seasonal effects are very complex, partly a combination of environmental (temperature, humidity), partly biological (there is also seasonality in the state of the human immune system and general health), partly human factors (more than we spent in poorly ventilated enclosures). This is undoubtedly an existing effect, but the change in the weather in the recent period has not been so drastic that it alone would explain the phenomenon.

• Weakening immunity – POSSIBLE

This is a major determinant of the future development of the epidemic. This is because the protection of the population not only increases (through vaccinations and vaccination), but also decreases over time. More and more publications are coming to light that after a few months, protection against infection weakens, but protection against serious illness remains for a long time. The weakening of immunity over time is taken by the newer our models van. However, this explanation is weakened by the fact that while Hungary was ahead of the other countries in the region in the spring mass vaccinations for a month, we were no longer ahead of the others in the trend reversal.

• Transient dynamics – UNlikely

There is a mathematical theoretical possibility that when we rearrange the structure of contacts (e.g. at the beginning of school), it has changed again from its previous trajectory, but in the meantime there is a transition period until a new growth rate is formed. In principle, it would be possible that what we see is a mere feature of nonlinear dynamics, but our model calculations with Hungarian contact matrices did not support this.

• Competition between respiratory viruses – POSSIBLE

Interestingly, the peaks of the epidemic of different seasonal upper respiratory viruses do not usually coincide, but follow each other almost on a regular basis: when one goes down, the other comes. Different viruses also compete with each other. Immunological factors play a role in this, have been shown for example, that individuals who are currently infected with rhinovirus are more difficult to infect with SARS-CoV-2 due to the immune response. But there is also an epidemiological aspect: if a virus causes a large number of illnesses in, say, school, many sick children stay at home, making it difficult for other viruses to spread. In September, GPs and pediatricians recorded a record number of patients with respiratory symptoms, but only a fraction of these were COVID-19. Thus, it is conceivable that an epidemic caused by other respiratory viruses prevented the spread of the coronavirus for some time, but this explanation is weakened by the fact that other respiratory viruses are still circulating in large numbers.

• Social heterogeneity – POSSIBLE

We have also seen significant differences in the involvement of certain social groups in previous waves. We also know that there are significant territorial inequalities in vaccination as well, and there have been regions in previous waves where the epidemic later reached. It is conceivable that the fourth wave has now reached better vaccinated, vulnerable groups that are spreading faster because of it.

Overall, several factors contributed to the rapid onset of the epidemic in October. Amongst these

there are reasons beyond our control, but the situation in which this affects us and what the consequences will be depends on the Hungarian epidemic control.

What’s coming now?

It is about three times more contagious than the virus that caused last fall’s epidemic against the delta variant, the current level of transmission (which is in European countries in Western European countries) alone is not enough. In Hungary, it would be very important to raise the vaccination rate, and as many of those already vaccinated as possible you should also request a third vaccination as soon as possible, as the data show that it provides a very high level of protection. We were among the first to start giving the third vaccine, and we are ahead of the other countries in this region to this day. The whole third or more is not a curiosity, even in the case of disease, the vaccination line already consists of three or even more doses, followed by permanent protection.

Current trends could lead to a serious situation in the short term.

Israel was in a similar situation at the end of the summer: the epidemic broke out at around 60% vaccination. This situation was solved by re-vaccinating one-third of the population in third place in a few weeks, and even tightening it, thus successfully breaking the wave caused by the delta variant. If we managed to boost the vaccination campaign again, it would help a lot to make our winter calmer, avoid new waves, and finally get out of the pandemic. The reality, however, is that the events of the critical weeks ahead of us can no longer be substantiated by a new vaccination campaign, because there is little time for that. If we want to mitigate the peak of the fourth wave cheaply, we need other tools, including wider use of masks and other risk-based targeted measures. Surely many are disappointed that, a year and a half after the pandemic began, we are in this situation again, but the sooner we face it, the better chance we have of avoiding more serious consequences.

Gergely Röst is a mathematician

Head of Department, Department of Applied and Numerical Mathematics, University of Szeged

Epidemiological Modeling and Epidemiological Analysis Working Group

This article reflects the views of the author and does not necessarily reflect the views of the Portfolio Editorial Board.

If you would like to comment on this topic, please send your comments to [email protected]. The Portfolio Opinion section is On The Other Hand. We wrote about the column here, and the published articles can be read here.

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