Why the jump in COVID-19 cases in Hungary? - Gergely Röst analyses reasons

Why did this happen? What is behind it?

We could wave away the answer by saying respiratory viruses are like that: they do not spread in the summer and spread in the autumn and winter months. However, for a realistic take on the situation, we have to evaluate how strong this seasonality is, how it is timed, and whether there are other reasons behind the current acceleration. At the end of the third wave, it was clearly visible that seasonal effects also helped end the wave quickly, and we were able to estimate the magnitude of these using models. During the summer, we were calculating scenarios showing that if this same seasonal change worked against us in the autumn, combined with lifting restrictions and a more virulent delta variant, the fourth wave would begin with a steeply rising curve unless vaccination uptake could be improved significantly. Compared to this, it was rather surprising to see how slow the growth was after the school year began, and the spread of the virus even slowed somewhat in the middle of September. As such, the real question is:

Why did this sudden change occur now?

Not just in Hungary

It should be noted that the October acceleration is not only characteristic of Hungary as there was a similar trend reversal in the entire CEE region at roughly the same time. This means there must be a factor that is present in the whole region. Of course, the magnitude of the change varies by country as each has a different immunisation rate from the previous waves and also different measures in place. Vaccination coverage also varies but is typically below the EU average.

In the following, we will examine the reasons that could potentially lead to the acceleration of a pandemic wave and see which of these could be at play in the current situation.

Possible reasons for the swift increase in new cases

• Looser measures – NO

As we have seen many times during the pandemic in various countries, the spread of the virus sped up after restrictions were eased or lifted. However, no such thing happened recently.

• Increased contact number – NOT LIKELY

The number of contacts between people can change regardless of government measures. In the UK, masses of young people filing the pubs during the football European Championship produced a peculiar curve that threw off even the best models. We are monitoring contact numbers in Hungary as well, both through online questionnaires and representative surveys. The number of contacts rose between April and the end of summer but has remained roughly unchanged since then, and mobility indices have not increased either recently. However, these surveys are not suited to assess the effects of individual mass events. Also, if higher contact numbers were the main answer, Hungary should be synched with other countries in the region.

• Official data exaggerate the severity of the pandemic – NO

The reliability of data has been a sensitive issue around the world throughout the pandemic. While there have been cases where official statistics painted a false picture about pandemic trends, these were typically underestimating the severity of the situation. At present, however, a number of indicators using independent sources are all pointing to a similar direction, so there can be no doubt that the situation is turning for the worse.

• More testing – NO

For a time at the beginning of the second wave, it was a popular misconception that the actual number of new cases was not growing and we were just finding more because of more tests. This was and is debunked by the increasing positivity rate of tests, which indicates that the correlation is reversed: the number of tests increases as there are more cases. The increasing positivity rate suggests that the number of confirmed cases underestimates the actual growth rate. Also, the load on hospitals is growing dynamically, which is independent of testing.

• Lower level of personal protection – NO

If a large number of people abandoned personal protection at the same time, it could lead to a sudden jump in case numbers. However we have seen the exact opposite in recent weeks as an increasing number of institutions re-introduced mandatory mask wearing. According to our surveys, the willingness to wear masks has increased in recent weeks, although it still remains below the required level.

• Spread of a new variant – NO DATA

When the alpha variant gained ground in January and February, it caused an increase in reproduction rate. With its low vaccination coverage, Eastern Europe is ideal ground for a variant that is able to circumvent existing immunity. In theory the current phenomenon could be caused by a new variant, but we have no information to confirm this. We should also add, however, that CEE countries are not in the vanguard of monitoring variants so it is questionable whether they would be able to detect a new variant emerging in the region.

• External effects – POSSIBLE

The pandemic situation is very serious in Southeast Europe, where vaccination coverage is low, and these countries are closely connected to the CEE region through mobility. It is conceivable that a large number of infected people from the Balkans have brought the virus with them, although such “imports” should not lead to a nationwide outbreak given a sound epidemic control system. In Hungary, there has been a major increase in new cases in the southeast part of the country, and the current situation in Germany is worst in the east and south parts of the country. The severe outbreak in the Baltic countries could also be correlated with the fact that the virus is not under control in neighbouring Russia.

• Seasonality, environmental factors – POSSIBLE

Seasonal effects are very complex and are a combination of environmental (temperature, humidity), biological (there is also seasonality in the immune systems and general health of people) and human (spending more time in poorly ventilated indoor spaces) factors. This is no doubt an existing effect, but the weather has not changed drastically enough in recent weeks to explain the phenomenon in itself.

• Weakening immunity – POSSIBLE

This factor may strongly determine the future development of the pandemic. The protection of the population is not only increasing (through vaccination and recovery) but is also decreasing with time. An increasing number of publications confirm that that protection against infection weakens considerably after a few months, but protection against severe symptoms remains high for a longer period. Our latest models account for weakening immunity over time. It should be noted, however, that while Hungary was about a month ahead of other CEE countries in the spring mass vaccination period, this no longer holds true in the autumn.

• Transient dynamics – NOT LIKELY

There is a theoretical mathematical possibility that when contact structure is rearranged (e.g. when school begins), the pandemic switches to anew trajectory, but there is a transitory period until the new growth rate solidifies. In theory, what we are seeing could be the peculiarity of non-linear dynamics, but model calculations using Hungarian contact matrices have not supported it.

• ‘Rivalry’ among respiratory viruses - POSSIBLE

It is an interesting phenomenon that the peaks of various seasonal viruses attacking the upper respiratory tract do not coincide, but they are successive: when one peters out, the next one emerges. Viruses also compete with one another. This also has to do with immunological factors. A study has found that an interferon response triggered by human rhinoviruses blocks SARS-CoV-2 replication. There is also an epidemiological aspect. If a virus causes a large number of infections in schools, for instance, then a lot of sick children stay home which makes it more difficult for other viruses to spread. In September, GPs and pediatricians reported a record number of patients with respiratory syndromes, but only a fraction of them had COVID-19. It is possible that the spread of coronavirus was stymied for a while by an epidemic caused by other respiratory viruses. This explanation, however, is undermined by the fact that a high number of various respiratory viruses are circulating as we speak.

• Social heterogeneity - POSSIBLE

There were significant differences in how strongly social groups were affected by coronavirus also in the previous waves. We are aware of the considerable geographical inequalities in respect of vaccination rates. Even in the previous waves there were regions that were affected by the pandemic with a delay. It is possible that the fourth wave has just found its way to vulnerable groups with low vaccination rates where transmission is consequently accelerated.

Overall, we can declare that various factors were at play during the surge in October. These included

causes beyond our control, but in what situation we will be when hit by the fourth wave and what consequences it will have hinge on the anti-pandemic defense measures.

What is next?

The current vaccination rate (lower than in Western Europe) itself is not enough against the Delta variant that is three times more contagious than the virus causing the pandemic wave last autumn. It would be of paramount importance to raise the vaccination rate in Hungary. Those that are fully vaccinated would need to register for their third dose as soon as possible, as data confirm that it offers an extremely high immunity level. Hungary was among the first countries to make third doses available, even before its regional peers. Third shots are not unique, the basic vaccination protocol can consist of three or even more jabs to build permanent immunity at various diseases.

The current trends can lead to severe conditions within a short period.

Israel was in a similar situation at the end of the summer, and the pandemic took off while 60% of its population were inoculated. They solved this situation by vaccinating one third of the population with third doses within a few weeks, and tightened restriction measures, successfully breaking the wave caused by the Delta variant.

Giving momentum to the vaccination campaign again would help us have a calmer winter, avoid new waves, and leave this pandemic behind at last. The reality is, though, that even a revived vaccination campaign could not possibly have a palpable impact on what is awaiting us in the critical weeks ahead; there is simply not enough time.

If we want to push the peak of the fourth wave significantly lower, we need other tools, as well. These include a wider-scale use of face masks and other targeted measures proportionate to the risks. It must be disappointing for many that we are in such a situation 18 months after the coronavirus outbreak, but the sooner we will face this, the better our chances will be to avoid even more severe consequences.

Gergely Röst, mathematician

Department Chair, Applied and Numerical Mathematics, University of Szeged

 Head of COVID-19 Epidemiological Analysis and Modelling Response Team

The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of Portfolio.

Cover photo: Vladimir Smirnov\TASS via Getty Images