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Vaccination against Sars-CoV-2 in Israel
Photo: Ammar Awad / REUTERS
When the new virus variant report from the Robert Koch Institute appears again this Wednesday, many can already imagine what will be read there: The spread of the worrying delta variant has also continued to increase in Germany.
Most recently, it had already caused at least half of all new infections.
There is little doubt that the mutant, first discovered in India, will sooner or later largely displace all others.
With the spread of Delta, the focus inevitably falls on regions in which it is already the predominant variant of Sars-CoV-2.
And news comes from there that has the potential to spoil the summer for Germans with the low incidences and only a few hundred new corona cases every day.
From Israel it is said that the effectiveness of the Biontech vaccine against Delta could be less than previously assumed.
The nation, admired for its rapid vaccination campaign, has already double-vaccinated the majority of adults and accordingly has extensive experience with the vaccine.
In addition, a lot of data from Israel was incorporated into studies.
Of the approximately 9.3 million inhabitants, 5.7 million people received the first vaccination, of which 5.2 million are fully vaccinated.
This corresponds to 56 percent of the population - but the country is still a long way from herd immunity, which according to estimates for the delta variant is around 85 percent.
According to the Israeli Ministry of Health, an increasing number of new corona infections have been observed across the country in the past two weeks.
At the end of last week, there were 334 cases in one day, the most that had not tested positive within 24 hours since April.
In addition, the increased increase goes hand in hand with the spread of the delta variant in Israel.
Their share is already more than 90 percent.
What does "only 64 percent" mean?
With regard to the effectiveness of the vaccinations, this means: Comirnaty, the agent from Biontech and its US partner Pfizer, probably only prevents infection and illness by 64 percent, hospital stays and severe courses to 93 percent.
For comparison: In February, the Ministry of Health in Israel had announced that the vaccine from Pfizer / Biontech prevented corona disease by 95.8 percent.
Typical symptoms such as fever and breathing difficulties would be prevented by 98 percent, hospital stays, serious illnesses and consequences of death by around 99 percent.
The decisive points for the evaluation of the vaccination protection are those for the prevention of symptomatic as well as severe courses.
The data from Israel are still preliminary and should be viewed with appropriate caution.
But what does a value of 64 percent mean in terms of effectiveness?
At least not that 64 out of a hundred vaccinated remain healthy and the other 36 percent get sick.
The figures relate to the individual risk - this is reduced by 64 percent.
But the individual risk is very different, because not everyone gets Covid-19 who is infected with the virus - courses without symptoms are also known.
For studies on the effectiveness of the vaccines, the researchers determined what is known as the relative risk reduction. The meaning becomes clearer with a look at the registration studies for the vaccines. The subjects were divided into two groups. One received two doses of the vaccine, the other an ineffective placebo each. Then it was looked at how many cases of Covid-19 occurred. For example, if a vaccine were to have no effect at all, there would have to be roughly the same number of cases in both groups. But so far, the studies have shown clear differences - there were far fewer Covid 19 cases in the drug groups.
Statisticians then calculate the effectiveness value by dividing the proportion of Covid-19 cases in the vaccination group by the proportion of Covid-19 cases in the control group.
In percent, the value indicates how much the vaccination lowers the risk of developing Covid-19.
It does not refer to the group of those who have been vaccinated, but to that of the infected (read more about this here).
Relative instead of absolute risk reduction
For example, if you achieve an effectiveness of 90 percent, that does not mean that nine out of ten people will be protected by a vaccination, or that with a vaccination rate of 100 percent in a country, 90 percent of the population will stay healthy and ten percent will get sick.
In order to find this value, which shows the absolute risk of infection, one would have to carry out studies in which one can be sure that the subjects would definitely get sick if they had not received a vaccination.
Such studies exist, they are called human challenge studies.
Although they are controversial due to their risks, they were also carried out during the research into Sars-CoV-2.
In the UK, for example, scientists wanted to re-infect young people who had already had the coronavirus in a targeted manner in order to find out what viral loads are required and how the immune system reacts.
Ultimately, an effectiveness of 64 percent would still be a good value.
For comparison: the vaccine from Johnson & Johnson comes up with similar, somewhat higher values;
Despite the risk of very rare cases of blood clots, the EU Medicines Agency Ema rates the benefits of the US vaccine as greater than the risks.
Many experts also see no cause for concern about the research results from Israel.
Even the chairman of the Israeli panel of experts on Covid-19, Ran Balicer, thinks it is too early to make precise statements about the effectiveness of the vaccine against the Delta variant.
Charité researcher Leif Erik Sander sees it similarly.
“You have to be careful with these numbers.
It is methodologically difficult to determine the exact effectiveness of the vaccination in such a setting as in Israel with low incidences and local outbreaks, ”says the virologist.
The virologist Alexander Kekulé judged that one shouldn't panic.
Because it is completely clear that the vaccines against new variants do not achieve the same effectiveness as against original variants.
Even with a lower level of vaccination protection, the immune system is in a better starting position than without vaccination.
There are also data that contradict those from Israel.
Results from the UK suggested that Delta's vaccination protection was only marginally reduced shortly after the second dose.
Accordingly, the vaccine from Biontech still achieved an effectiveness of 88 percent and that of AstraZeneca 67 percent.
However, Sander fears that the delta variant can lead to so-called breakthrough infections more frequently.
Experts speak of this when people who have been vaccinated twice fall ill.
The effect has already been observed in Great Britain, where people who had already received full immune protection also died.
Such observations can in part also be explained by statistics: the more people are vaccinated, the more often it will be noticed that the vaccines are not perfect. And deaths are also to be expected. However, the preliminary figures from Israel give cause for hope on this point, as 93 percent of the vaccine still ward off serious illnesses and hospital stays. The study from Great Britain had shown something similar. The data expert Eran Segal from the Israeli Weizmann Institute of Science in Rechovot does not expect as many difficult courses and hospital stays in the future as there were at the peak of the pandemic because of the vaccinations.
The data from Israel may also show that vaccination protection is already waning in some parts of the population, says US expert Andy Slavitt on Twitter.
Older people in particular are suspected here.
After all, the vaccinations for older Israelis were a long time ago compared to other countries.
A third vaccination in autumn, the so-called booster vaccination, could help here.
It will probably not be necessary for the entire population, but in the opinion of most experts it could make sense for vulnerable groups.
with material from dpa