This is what researchers say in a new study aimed at explaining the success of the delta variant.

In December 2020, a new variant of the coronavirus SARS-CoV-2 appeared in India. In the months that followed, the variant – referred to as the delta variant – spread rapidly. And in many countries – including the Netherlands – the lion’s share of infections is now caused by this variant.

The success of a corona variant explained

But how exactly can the rapid advance of this variant be explained? A new study – published in the magazine Nature – creates more clarity. “We show that the delta variant multiplies and spreads more easily than other widely observed variants,” said researcher Ravi Gupta, of the University of Cambridge. “There is also evidence that neutralizing antibodies resulting from a previous infection or vaccination are less able to stop this variant.”


Gupta and colleagues base their conclusions on laboratory experiments, among other things. Serum from people who had already had the coronavirus or had been vaccinated with the Astrazeneca or Pfizer vaccine were used for this. This serum contained antibodies produced in response to vaccination or previous infection. And the researchers examined the extent to which these antibodies were able to trap the delta variant. The experiments show that the delta variant was 5.7 times less sensitive to serum from people who had experienced a previous infection compared to the alpha variant (also called British variant). In addition, the delta variant – again compared to the alpha variant – turned out to be up to eight times less sensitive to serum from vaccinated people. In concrete terms, this means that 5.7 and 8 times more antibodies are required respectively to stop the delta variant.

In practice

The results of the laboratory study are supported by an analysis of 100 healthcare workers who work in three different hospitals in Delhi and – despite almost all of them being vaccinated – all became infected with the delta variant. The analysis shows that the delta variant spreads more easily among vaccinated personnel than the alpha variant did before.

Multiply and Spread

But the variant is not only less impressed with our antibodies obtained either from a previous infection or vaccination. The delta variant also multiplies and spreads more easily, experiments show. For these experiments, the scientists used mini-organs made up of cells from human airways. These mini-organs actually behave just like our airways. And by infecting them with the delta variant, the researchers were able to get a better picture of the behavior of the virus. The experiments show that the delta variant is better able to penetrate our cells and – once inside – can also multiply much more easily.

The key to dominance

According to the researchers, the study can help explain how the delta variant has become the dominant variant in a short time in many countries. “The delta variant has spread widely and has become the dominant variant globally because it spreads faster and is more capable than most of the other variants we’ve seen at infecting individuals,” said study researcher Partha Rakshit. “Also, (the variant, ed.) it is easier to bypass existing immunity – whether through previous exposure to the virus or vaccination – although the chance of moderate to severe disease is smaller in such cases.”

The research has important implications for our future fight against the coronavirus. Because that battle is not yet won. For example, the researchers point out that it is important to adapt existing vaccines in such a way that they are more effective against (new) variants. These more effective vaccines are particularly needed in hospitals and healthcare institutions, according to researcher Anurag Agrawal. “Infection of vaccinated healthcare workers by the delta variant is a major problem. Although they may only develop mild symptoms themselves, there is a chance that they infect individuals whose immune response after vaccination is not optimal due to underlying health problems. And those patients run the risk of becoming seriously ill. We urgently need to think about ways we can improve the vaccine-induced immune response among health professionals.” In addition, the research strongly points out that the corona measures aimed at limiting the spread of the coronavirus are not yet immediately superfluous in the light of this variant. this is how the researchers write.