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Why is there such a strong East-West incidence gradient?

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Status: 05.07.2022 10:19 a.m.

Incidences in the eastern federal states are currently much lower than elsewhere. In conspiratorial circles, this is explained by the lower vaccination rate. What are the real causes?

By Anna Behrend, NDR, and Pascal Siggelkow, ARD Investigator Editors

The national seven-day incidence in Germany has been increasing significantly for several weeks. Federal Health Minister Karl Lauterbach has already spoken of a corona summer wave. But when you look at the developments, you notice that there are huge differences between the federal states. While the incidences in Lower Saxony and Schleswig-Holstein have already exceeded the threshold of 900, the values ​​in Thuringia and Saxony are still below 400.

In general, it can be seen that all states in eastern Germany – with the exception of Mecklenburg-Western Pomerania – are even well below the national incidence of 687.7. And this despite the fact that Saxony, Brandenburg and Thuringia are among the taillights when it comes to vaccination rates. In conspiratorial circles, there is already talk of “negative protection”, in particular vaccination reminders, and the figures would impressively prove the ineffectiveness of vaccinations. But is there really a causal relationship between vaccination coverage and incidence?

Vaccination protects against serious illness and death

One thing is certain: unvaccinated people who are infected with the corona virus have a significantly higher risk of having to be treated in an intensive care unit or of dying than vaccinated people. This applies to both the Omicron variant currently in circulation and the Delta variant that prevailed in autumn and winter last year. For the past year researchers from Jena, among others, have examined excess mortality in the German federal states and linked them to regional vaccination rates. The conclusion: where the vaccination rate was high, the excess mortality was relatively low. Vaccination therefore remains a crucial factor in preventing the health system from being overburdened.

Many vaccine breakthroughs with the omicron variant

However, since the severity of the course of an infection is irrelevant to incidence, it depends on so-called vaccination breakthroughs – i.e. whether people become infected despite the vaccination. In the case of the Delta variant, available vaccines provide relatively good protection against symptomatic infection. This could be one of the reasons why the incidence numbers from last winter’s delta wave behaved regionally the opposite of what they are today: at that time they were low where the vaccination rate was high.

The situation is somewhat different with the omicron variant: vaccination protects against a severe course and death from Covid-19, but according to information from the RKI, it hardly protects against an infection itself.

In any case, the distinction between vaccinated and unvaccinated people in the development of the infection process becomes less and less useful, explains Johannes Knobloch, specialist in microbiology, virology and infection epidemiology at the University Hospital Hamburg- Eppendorf (UKE). Due to the extremely high number of cases, many unvaccinated people would have had at least one contact with Covid-19. “In the meantime, additional infection has also occurred in many vaccinated people. In order to make a full statement, one would have to compare many subgroups with each other.”

Some studies indicate that vaccinated people infected with Omicron are slightly less infectious than unvaccinated people, but so far there is not enough data to make a conclusive assessment. The following applies to all variants of the virus: There is no scientific evidence that vaccination promotes infection with the coronavirus.

Only limited impact

However, if the vaccination rate in the omicron wave is not the decisive factor for the development of the incidence, how come the number of new infections in the eastern federal states is currently relatively low?

First of all, it should be noted that current infection numbers have only limited significance. “You should always remember that incidences are calculated based on reported lab results,” says Knobloch. As before, only positive PCR tests count in the RKI statistics. The willingness to be tested and the accessibility to PCR tests therefore currently have a very great influence on the incidence measured. Their importance is therefore “only very limited”. “The number of unreported cases is currently likely higher than any previous phase of the pandemic.”

According to experts, however, it can still be seen whether the wave of infection is increasing or decreasing from the incidence. However, caution should be exercised when making regional comparisons, as the testing strategies and thus the number of tests in the federal states differ significantly. Fewer tests also means fewer infections detected.

A high proportion of positive tests is therefore also an indication of a high number of unreported cases, such as in Bremen (86%) or Thuringia (55%). But it is by no means true that all eastern federal states have a suspiciously high positive rate compared to others. The different testing procedures alone cannot therefore explain the currently low incidence in this country.

Federal states in the East already more infected?

If the incidence was in fact much higher, one would also expect this to also be noticeable in intensive care units a few days later. Because a certain proportion of all infected people suffer a severe course and need to be treated in hospital. However, the proportion of Covid patients in intensive care units is currently not noticeably high in a national comparison in the eastern federal states.

So maybe most people in low incidence countries were already infected and are now immune? Anyone infected with the corona virus usually forms antibodies against it. The duration and quality of protection against re-infection with the virus has not yet been conclusively studied. However, assuming there is protection for at least some time, one conceivable reason for the low incidence in some federal states would be that more people there have had contact with the virus in the past and are therefore less likely to to be infected.

Due to a lack of studies, it is not known exactly how much of the population in the federal state is already infected with the virus. If the number of new infections per 100,000 population since the beginning of the year is considered as a rough approximation of the infection with the omicron variant currently in circulation, the assumption that the population of the federal states of Est is already more in contact with her is not confirmed. Only Mecklenburg-Western Pomerania has recorded a fairly high number of infections per capita since the start of the year in a national comparison.

Regional appearance of new variants

One of the reasons the incidences are rising so sharply nationwide is the omicron BA.4 and BA.5 subtypes. Experts consider them to be more contagious than the previously known “sister variants”. BA.5 now dominates in Germany with 65.7%, and the trend is clearly on the rise. It can therefore be assumed that the number of new infections will continue to increase in the coming weeks.

In which federal states the new subtypes are already widespread has not been published by the RKI since April due to too few samples. A comparison would no longer make sense due to excessive fluctuations. Nevertheless, it is of course possible that some federated states are already more affected by the new subtypes than others, which could still be. Other factors such as population density and contact behavior also influence the spread of the virus and therefore the seven-day incidence.

“Since autumn of last year, we have observed different epidemiological developments in the individual federal states, so that we no longer expect parallel developments in the incidence curves in all federal states,” explains Knobloch. “Newly emerging variants or sub-variants may only make themselves felt in other regions a few weeks later.”

How the virus spreads and the incidence measured regionally depends on many factors. What is certain, however, is that there is no scientific basis to assume that a high vaccination rate can be partly responsible for a high incidence. On the contrary: the scientific data tends to indicate that vaccinated people infected with omicron infect other people somewhat less frequently than unvaccinated people.

Source www.tagesschau.de

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