South Africa has experienced two waves of infection with the virus, the first peaking in July 2020, caused mainly by the D614G variant. The second is, of course, almost entirely caused by the 501Y.V2 variant, with peak levels in January 2021. Several earlier studies have shown that the latter variant is resistant to polyclonal antibodies induced by vaccination or natural infection with other variants, though the extent of resistance varies with the strain. In clinical trials with the Novavax NVX-CoV2373 subunit vaccine, the efficacy dropped from 89% to 49%, while there was no difference in infection rates between those who were seropositive and seronegative. In other words, earlier viral lineages did not protect against infection with the above VOC (variant of concern).
Again, with the Johnson and Johnson adenovirus vectored vaccine, the efficacy following a single dose was 75% in the US but only 57% in South Africa. The Oxford/Astra-Zeneca adenoviral vectored virus also showed only 10% efficacy against this VOC vs. 75% for the earlier variants. A study used a live virus neutralization assay (LVNA) to compare the neutralization achieved by infection with this VOC compared to earlier variants. Using the PRNT50 values, they found that the first-wave plasma cross-neutralization of this second-wave variant was markedly reduced to 41, indicating a drop by 3 to 42-fold.
Overall, the PRNT50 was 344 for homologous first-wave CP and first-wave variants, while with second-wave CP and second-wave variant, the PRNT50 was 620. The findings show that 501Y.V2 is equipped to escape antibody neutralization by antibodies produced against other variants of SARS-CoV-2. On the other hand, antibodies elicited by 501Y.V2 effectively neutralize both this variant and earlier lineage.
The cross-neutralization range was within the lower half of the range of neutralization elicited by the Pfizer mRNA vaccine. Given the high PRNT50 of second-wave plasma, this variant appears to be more immunogenic.
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