Delta variant shows 8-fold sensitivity to vaccine elicited antibodies: Study

The Delta variant of Covid-19 virus shows eight-fold approximately reduced sensitivity to vaccine elicited antibodies compared to the Wuhan strain, revealed a recent study on the B.1.617.2 Delta variant on over 100 healthcare workers (HCWs) across three centres in Delhi, including Sir Ganga Ram Hospital.

As per the study, the variant is less sensitive to neutralising antibodies from recovered individuals, with higher replication efficiency as compared to the Alpha variant. The study is available online as a non-peer reviewed preprint version in Research Square, an expanded set of services and tools for expert research assistance.

It is a collaborative study involving scientists from the Cambridge Institute of Therapeutic Immunology and Infectious Disease.

In an analysis of vaccine breakthrough in over 100 HCWs, a statement issued by Sir Ganga Ram Hospital based on the outcome of the study said that across three centers in India, the B.1.617.2 Delta variant not only dominates vaccine-breakthrough infections with higher respiratory viral loads compared to non-Delta infections (Ct value of 16.5 versus19), but also generates greater transmission between fully vaccinated HCWs as compared to the other variants B.1.1.7 or B.1.617.1

The Delta variant, first detected in India, is now being reported in nearly 100 countries, which is “likely an underestimate” and the highly transmissible strain is expected to rapidly outcompete other variants and become dominant globally over the coming months, the WHO had said last week.

According to Chand Wattal, Chairperson, Institute of Clinical Microbiology and Immunology, Sir Ganga Ram Hospital, “From this study it appears that we have to go miles before we sleep in case of the Covid-19 pandemic. These mutations are bound to happen if we lower our guard and allow ourselves to fall prey to this virus, giving it an opportunity to multiply and achieve better fitness with our Covid inappropriate behaviour. This is a straight eye opener for the fully vaccinated people that you cannot lower your guard in the name of vaccination. The virus is still looking of its prey.”

Wattal said the mutant has come back with enhanced spike proteins for attachment to the lung epithelial cells which has provided it much higher capacity to infect many more people than the Wuhan strain.

“These combined epidemiological and in vitro data indicate that the dominance of the Delta variant in India has been most likely driven by a combination of evasion of neutralising antibodies in previously infected individuals and increased virus infectivity resulting in the second wave.

“While severe disease in fully vaccinated HCWs was rare, breakthrough transmission clusters in hospitals associated with the Delta variant are concerning and indicate that infection control measures need to continue in the post-vaccination era.

“The B.1.167.2 Delta variant appears more transmissible than B.1.1.7 in the UK based on recent data and the dominance of new infections by this variant,” Wattal said.

In the absence of published data on the transmissibility of the Delta variant, the study predicts that this variant will have a transmission advantage relative to Wuhan-1 with ‘D614G’ in individuals with pre-existing immunity from vaccine and natural infection as well as in settings where there is low vaccine coverage and low prior exposure.

Lower protection against B.1.351, the variant with least sensitivity to neutralising antibodies, has been demonstrated for at least three vaccines. However, progression to severe disease and death was low in all the studies.

Therefore, extensive vaccination will likely protect against moderate to severe disease and will reduce hospitalisation due to the Delta variant.