Vaccines less able to neutralize Delta In the second study, published yesterday in Cell, a team led by University of Oxford researchers evaluated whether vaccines, monoclonal antibodies, or antibodies derived from COVID-19 survivors could neutralize the Delta variant's B1617.1 and B1617.2 sublineages. They exposed the Delta variants to neutralizing antibodies from vaccinated participants, convalescent sera from UK COVID-19 patients from early in the pandemic, and monoclonal antibodies. They also looked at the affinity of the variants' receptor-binding domains for angiotensin-converting enzyme 2 (ACE-2), which allows the virus to enter human cells. The researchers found substantial reductions in the ability of the AstraZeneca/Oxford and Pfizer/BioNTech vaccines to inactivate the Delta variant, although the viruses weren't broadly able to escape neutralization. The ability of the Pfizer vaccine to neutralize the Delta variant dropped 1.34-fold between 4 and 10 weeks after the first dose, at which time the ability was nearly lost. "Recently in the UK some reduction in Pfizer-BioNTech effectiveness has been detected at 10 weeks, presumably as a result of waning immunity, leading to the recommendation that the second vaccine dose interval should be reduced from 12 to 8 weeks in those over age 50," the authors said. The researchers noted previous studies that found lower vaccine effectiveness against mild to moderate COVID-19 in countries in which Beta (B1351) was dominant, as well as against the Alpha (B117) variant first seen in England, although protection against severe illness was maintained. Overall, convalescent sera was 4-fold less effective against B1617.1 and 2.7-fold less effective against B1617.2 than against an early strain from Wuhan, China. Still, convalescent sera containing antibodies against the Beta variant first seen in South Africa and the Gamma (P1) variant first identified in Brazil were the least able to inactivate Delta. Data showed that the Delta variant's affinity for ACE-2 was slightly enhanced compared with that of the Wuhan strain as well. "Individuals previously infected by these variants may be more susceptible to reinfection by B.1.617.2," the authors wrote. "This observation provides important new insight for immunization policy with future variant vaccines in non-immune populations." Continued emergence of new variants The authors said that the true number of SARS-CoV-2 variants probably has been underestimated and that more variants of concern will continue to emerge. "Early in the pandemic SARS-CoV-2 was under selective pressure to adapt to its new host, to evade the innate immune system, to efficiently bind to and infect target cells and to transmit to the next host," they wrote. "As the population develops immunity, by either natural infection or vaccination, pressure is mounting to select mutations that allow the virus to more effectively find an infectible host through increased transmissibility, or to evade the acquired immune response and cause reinfection." The authors called for more epidemiological data on how often breakthrough infections occur after escape mutations and whether they will cause severe disease and hospitalization. "If this escape from the neutralising capacity of vaccines continues with evolution of new variants in vaccinated populations, and leads to a substantial reduction in effectiveness against hospitalisation, there will be a significant impact on attempts to alter the course of the pandemic through immunisation and an urgent need to revise immunogens," they concluded.
more