Falling corona incidence values
–
“It cannot be vaccinated alone” – as modelers explain the current development
05/29/21 | 8:10 am
The corona situation has been improving significantly for a few weeks. In many circles the incidence is below the limit values. But how could that happen so quickly? A search for explanations. By Haluka Maier-Borst
–
Too slow, too sluggish, too little. Be it the vaccination speed, be it the decision of the federal emergency brake or other measures. Much criticism was heard from January to April, while the number of cases continued to rise. And now? The incidences have been rushing down for weeks. The relief is great, but so is the perplexity. Because the fact that the turnaround has been achieved so clearly surprises many, also against the background of the more contagious coronavirus variant B.1.1.7.
So why is the situation improving so rapidly in Berlin, Brandenburg, Germany, and indeed all of Europe? rbb | 24 carefully looked for explanations.
–
1. The vaccination
Vaccination works. That can be read again and again and is true in two respects. On the one hand, those who have been vaccinated fall ill less often, regardless of whether it is now sprayed with Astrazeneca, Pfizer-Biontech, Moderna or Johnson & Johnson. But they also pass the virus on much less often, even when they become ill. This was shown by a study by the British health authority PHE [khub.net].
And yet that alone cannot explain the current decline, especially not the trend reversal at the end of April. At this point in time, only around a quarter of Germans had had a vaccination. Too few to explain such a change.
If you cannot see the graphics, please click here.
–
In addition, the elderly were first vaccinated. That makes sense because you so saves the most lives per vaccination. At the same time, however, the old have fewer contacts than the young. So vaccinating them is less of a brake on the pandemic.
Dirk Brockmann, epidemiological modeler at the Humboldt University in Berlin, illustrates it this way: “If the herd immunity is around 80 percent and you have already vaccinated 40 percent, as it is now, that doesn’t mean that you are halfway through the way the contacts are distributed is significantly less. “
You can tell that the vaccinations are a deceptive argument if you look, for example, at how incidences have developed in Israel and Great Britain. If you look at the graph, you might get the impression that Great Britain was ahead of Israel in terms of vaccinations. In fact, it was the other way around.
–
The example of Israel-Great Britain illustrates something that the modelers and other experts have repeatedly emphasized: There is no single measure that lowers the numbers. It is the mix of measures that differs quite a lot between countries.
The fact that incidences fell in Israel from mid-February fits in well with the fact that around half of the population was vaccinated by that time. That this was also the main reason in Great Britain and currently works as a key explanation in the rest of Europe is rather unlikely.
Peter Klimek, who works as a modeler at the Medical University of Vienna and advises the Austrian government, quantifies the effect of the vaccinations roughly as follows: “We assume that at the current vaccination rate you will vaccinate half a percent to one percent of the R value every week , which is relevant for new infections. So vaccination alone cannot be, that would be too little, “he says.
–
2. The measures
The above example of Great Britain therefore shows better how effective measures can be. The particularly long and strict lockdown was probably the main reason why you could reduce the numbers faster than Israel despite fewer vaccinations per capita [ft.com]. A fact that British Prime Minister Boris Johnson also seems to be clear in the meantime [guardian.co.uk].
And in some cases, the measures also work as an explanation in this country. It is correct that measures were tightened well before the federal emergency brake. Something similar happened in other parts of Europe. “The increase due to the more contagious variant B.1.1.7 was flatter than in many other countries around the world,” says the Viennese modeler Klimek. In addition, the increasing availability of tests has led to fewer and fewer infections going undetected.
His Berlin colleague Brockmann also refers to feedback effects. Because the numbers are rising and there is more discussion about tightening measures, people are restricting their behavior more. An effect which was demonstrated in several studies more than ten years ago [royalsocietypublishing.org] and was discussed [pnas.org]. That this effect is quite large was already seen, for example, with the first lockdown last year. There, mobility sank even before the measures came into force.
–
There is currently still a slight decrease in mobility compared to 2019 [covid-19-mobility.org]. Not significantly more than in previous months, however. It is therefore also conceivable that the number of activities did not necessarily decrease – but with more measures such as mask, distance, quick test and the like.
Nevertheless, the Viennese Klimek admits that despite vaccinations and the tightened measures, the current downward trend is surprising. “The development is already within the scenarios we thought possible a few weeks ago. But it was one of the less likely,” he says.
–
3. The seasonality
Klimek therefore suspects that seasonality is an underestimated factor and explains why this could be despite the rainy months. “When we talk about seasonality, we usually only think about the fact that more meetings take place outside than inside. But there are also other aspects. If, for example, we heat less and thus dry out the aerosols with the virus particles less, they can stay in the for less Air floats. The result: You stay in the air for a shorter time and the risk of being infected in the room is lower, “he says.
Stronger UV light and a generally stronger immune system in spring could also play a role. “I still see a lot of homework ahead of us to understand all of this better,” he says.
Brockmann also believes that seasonality plays an important role. But he emphasizes that you have to see it in combination with all other aspects. The effects added up and it could of course be that the better weather now brings the decisive effort to reduce the number of new infections. But in the USA last year and the outbreaks there, you have also seen that if you let it slip with other measures, seasonality alone will probably not be enough.
–
4. What remains unclear
Brockmann therefore sees the greatest uncertainties in another area: the structure of contact networks. “We know very little about how people interact with each other in a society. So not just how many people you meet in a week, but how all these people are related to each other and, for example, how often someone is among them who have a virus in several Households could carry on, “he says.
The two researchers agree, however, that there are still many imponderables, from further mutations, vaccine skepticism to delivery bottlenecks for vaccinations. Accordingly, one has to be careful with models.
It is true that these are significantly better than they are currently being discussed. For example, in a modeling that discussed the effect of bringing forward first vaccinations, incidences of less than 30 to 50 were considered possible, says Brockmann. Any scenario that tries to look into the future for longer than three to four weeks is basically doomed to failure.
–
