Corona vaccination: how much does the protection decrease? – The risk of infection for vaccinated people in Israel was around ten percent after five months –

Specific figures: A study with a good 80,000 people vaccinated in Israel provides a more detailed insight into how much the immune protection of an mRNA vaccination against SARS-CoV-2 decreases. Accordingly, the vaccination protection against Covid-19 remains largely stable in the first three months. Then the risk of infection gradually increases despite the vaccination. After five months, the rate of infected people was a good ten percent – but not all of them also contracted Covid-19.

The vaccination against the SARS-CoV-2 coronavirus has so far been our sharpest weapon against the corona pandemic. The mRNA vaccines in particular protect over 90 percent against severe courses of Covid-19 – at least initially. But it is now clear that the vaccine is waning. The number of vaccination breakthroughs – symptomatic Covid-19 cases in vaccinated people – is increasing worldwide.

One of the reasons for this is the more infectious delta variant, and another is the decreasing “vigilance” of our immune system: As less and less antibodies and T cells specific for SARS-CoV-2 circulate in our blood, it takes longer for the immune system to react . Especially for the rapidly increasing delta variant, this delay is then sufficient to gain a foothold in our body.

Israel as a model case

But how quickly and how strongly does this reduce the immune protection? This is now shown by a study from Israel, in which researchers working with Ariel Israel from the Leumit health insurance company evaluated the data of more than 80,000 vaccinated people. They compared how many of these participants were positive in a PCR test despite being vaccinated, and how this proportion changed as the time interval between their second vaccination dose increased.

“Israel was among the first countries to carry out a large-scale vaccination campaign,” the researchers explain. By using the mRNA vaccine from BioNTech / Pfizer, a very broad immunization of the population was achieved very early on. At the same time, Israel was also one of the first countries in which the corona numbers rose again despite vaccination – the incidences began to rise again as early as June 2021. The team therefore investigated how this was related to the declining immune protection.

Infections in vaccinated persons by age group and interval from the second vaccination dose. © Israel et al./ BMJ, CC-by-sa 4.0

First plateau, then steady decrease

The result: In the first three months after the second vaccination dose, the proportion of corona infections was around 1.3 percent. Because the participants were tested routinely in some cases, these positive cases also included many asymptomatic infections. “This confirms the excellent protective effect of the mRNA vaccine in the first few weeks after vaccination,” say the researchers.

In the fourth month, however, the infection rates began to increase measurably: The number of positive tests was now 2.4 percent – almost twice as high. In the fifth month, the rates rose to 4.6 percent. The vaccination protection then fell even more significantly from the fifth month: In the period from 150 to 179 days after the second vaccination dose, the infection rate was 10.3 percent, after more than 180 days it rose to 15.5 percent.

“Booster” advisable

These results confirm that the vaccination protection of the mRNA vaccination against SARS-CoV-2 decreases continuously from about the third month. After six months, the risk of infection despite the vaccination is a good 15 percent. However: The study only examined the infection rate, but not how severe the Covid 19 symptoms were in these re-infections or whether the participants had any at all.

According to the research team, however, these results underline that a booster vaccination makes sense from around the fifth month – if only to curb the further spread of the coronavirus. Because even if infected people do not become ill themselves despite being vaccinated, they can pass the virus on to others. Exactly this effect is considered – besides those who are still unvaccinated – as one of the drivers of the current fourth wave here in Germany. (British Medical Journal (BMJ), 2021; doi: 10.1136 / bmj-2021-067873)

What: BMJ

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