The Delta and Delta Plus COVID-19 variants were less well neutralised by antibodies from infected and vaccinated individuals as compared to the original virus, making them more dangerous and contributing to its rapid global spread, according to a study.

The Delta variant (B.1.617.2) first emerged in India during 2020 and subsequently spread globally within a short time period. In addition to Delta, Delta Plus sub-variants have been observed which carry additional mutations that may make them more dangerous. In the study published in the journal Cell Reports, the researchers showed that both Delta and Delta Plus infect lung cells with higher efficiency than the original virus (the virus that circulated during the early phase of the pandemic).

The Delta COVID variant was found to be better at entering lung cells compared to the original virus and also at fusing infected lung cells with uninfected cells. This enabled the variant to spread widely and infect more people.

"It is conceivable that by fusing cells in the respiratory tract, the Delta variant may spread more efficiently and induce more damage. This could contribute to a more severe course of COVID-19," said Arora Prerna, Scientist at the German Primate Center -- Leibniz Institute for Primate Research in Gottingen, Germany.

Moreover, one of four antibodies (bamlanivimab) used to treat COVID-19 was not effective against Delta, and Delta Plus was even resistant against two therapeutic antibodies (bamlanivimab and etesevimab). Similarly, antibodies generated upon vaccination with the BioNTech-Pfizer and Oxford-AstraZeneca vaccines were also less effective against Delta and Delta Plus compared to the original virus.

"Our results are consistent with the observation that vaccination efficiently protects against the development of severe disease after infection with the Delta variant, but frequently fails to completely suppress infection. In light of the efficient protection against severe disease, the goal continues to be a high vaccination rate. This can prevent the healthcare system from being overwhelmed in case of increased spread of Delta and closely related viruses during the winter months, "said Stefan Pohlmann from the German Primate Center.