The delta wave is increasingly keeping governments around the world in suspense, but the spread pattern of the Sars-CoV-2 variant originally discovered in India is by no means the same everywhere.
The World Health Organization (WHO) has recently reported a significant increase in the number of cases and a renewed flare-up of the infection rate with almost 4.4 million Covid-19 victims.
According to the WHO, more than 90 percent of the samples that were gene-sequenced in the past four weeks belonged to the delta variant.
However, not all countries still provide enough data to be able to attribute the third global pandemic wave to the highly infectious delta variant without a doubt.
Joachim Müller-Jung
Editor in the features section, responsible for the “Nature and Science” section.
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At least that's what the statistics suggest: According to them, the vast majority of the increases in infections, diseases and deaths are reported from North America with a delta proportion of more than 90 percent, especially from the United States, where especially those with extremely low vaccination rates and loose Corona rules waiting states in the south - from Florida to Louisiana and Texas - experienced the highest increases after the fall wave last year. Also in Asia, Africa and Australia - albeit with lower incidences than in the United States - as well as in parts of Europe it can be said on the basis of the genome analyzes: Delta is exploiting its threateningly infectious potential, which was demonstrated in laboratory studies and in the months after the India wave epidemiological investigations has become recognizable.
Since then, the warning has always sounded similar: Because Delta is at least twice as infectious as the virus of origin due to its mutations, multiplies more quickly in the mucous membranes of the upper respiratory tract and may remain contagious for longer, full vaccinations have top priority.
Are the vaccines no longer working?
But the question marks are increasing - and that is due to the latest developments in incidences and disease rates. Ironically, the situation in India, which registered more than 400,000 infections daily during the worst delta wave in spring, has been stable for weeks. Only six percent of the billion people are still fully vaccinated. However, as an antibody sample suggested by the government in June and July, two thirds of the population could have had contact and at least temporary immune protection. In February, antibodies had only been detected in a fifth of Indians. This could at least theoretically explain the epidemic calm that the subcontinent is currently experiencing with only a tenth of new infections.
In fact, some experts want to explain the steep drop in the violent delta wave observed in parts of Great Britain at the end of July - despite the easing towards summer. In some areas, up to 90 percent antibody immunity has been found on the island. So herd immunity already? Most experts are skeptical because immunity and the spread of the virus on the island are very different. The same applies to India: in many densely populated metropolises, the Delta is obviously still expanding.
The delta increases are not unexpected in some Asian countries, where Sars-CoV-2 has been kept under control for a long time - also in Australia.
There the vaccination progress was lame for a long time, the proportion of unvaccinated people is high, especially among the middle and young cohorts.
But what, so the experts wondered for the first time in mid-July, then happens in the vaccination model country Israel with a vaccination coverage rate of more than two thirds - and what also happens in Iceland and Malta, where the vaccination rate is a good 90 percent - where there are now even many Do vaccinated people get sick?
Are the vaccines no longer working?
In the elderly, immunity can wane after a few months
The protection against serious illnesses and death with the approved vaccines, there has been little doubt about this so far, is still extremely high, even with Delta. However, the vaccines are not perfect when it comes to contagion. Younger unvaccinated people, including children, are more likely to get the disease, as recent data from the United States show. Above all, however, it affects many of the fully vaccinated in Israel. Two thirds of the last 400 Israeli clinic patients in critical condition were vaccinated, one third were unvaccinated. This is by no means unexpected for immunologists. Israel had vaccinated nearly two million people at risk by the end of January, mostly old and very old people over 65 years of age. With these, however, and especially with those over eighty, this is now also clear from the data of German scientists,immunity can decrease significantly after a few months. The antibodies in the blood are broken down and there are fewer of the helpful T immune cells due to age.
The loss of immunity thesis is supported by new, but still provisional, data from the booster vaccinations for people at risk in Israel: Among the more than 600,000 citizens who have received a third dose of vaccine since the end of July, the delta wave measured in the number of cases has apparently broken - unlike the rest of the population. In fact, the proportion of seriously ill among those under sixty and over sixty is expected from the vaccination studies: a clear minority of those vaccinated fall ill.
According to the Israeli corona specialist Dvir Aran, the vaccine effectiveness against Delta of almost 90 percent is achieved in the younger age groups. But at least in some of them, the vaccination protection is already reduced to such an extent that the risk of infection is slightly increased. However, the rumors that emerged with the first delta analyzes that vaccinated people also infect others have not yet been clarified in previous studies.