Pfizer's COVID-19 vaccine stimulates lower antibody response against B.1.351 strain

Preliminary findings from an in vitro study published Wednesday in the NEJM showed that Pfizer and BioNTech's COVID-19 vaccine BNT162b2 elicited roughly two-thirds lower levels of neutralising antibodies against a highly transmissible SARS-CoV-2 variant that was first spotted in South Africa. However, the authors said it remains "unclear" what such a reduction in neutralisation would have on BNT162b2-induced protection from infections caused by the B.1.351 lineage of the virus.

Last month, Pfizer and BioNTech reported results from another laboratory study in which BNT162b2 appeared effective against the so-called UK strain known as B.1.1.7. For the latest work, researchers produced three genetically engineered recombinant viruses, with one having the full set of spike glycoprotein mutations found in the South African variant (B.1.351-spike), while the other two had subsets of these mutations. They tested the viruses using 20 serum samples obtained from 15 people who had been immunised with BNT162b2 as part of the pivotal Phase III trial of the mRNA-based vaccine.

'No clinical evidence' of viral escape

The authors reported that when compared to a relatively early isolate of SARS-CoV-2, neutralisation of the B.1.351-spike virus was weaker by approximately two thirds. Specifically, geometric mean neutralising titers against the early strain and the South African variant were 501 and 184, respectively. However, "the onset of protection after one dose of BNT162b2 precedes the development of high neutralising titers, and BNT162b2 immunisation also elicits CD8+ T-cell responses," the researchers wrote, "thus, it is unclear what effect a reduction in neutralisation by approximately two thirds would have on BNT162b2-elicited protection from COVID-19 caused by the B.1.351 lineage."

In a statement, Pfizer and BioNTech said "there is no clinical evidence to date that the South African variant virus escapes BNT162b2-elicited protection from COVID-19 in vaccinated people." Still, the companies indicated that they are "taking the necessary steps…to be in a position to develop and seek authorisation for an updated mRNA vaccine or booster once a strain that significantly reduces the protection from the vaccine is identified."

Testing against Brazil variant

Further, Pfizer and BioNTech said they are evaluating the ability of BNT162b2 to protect against spike mutations of the P.1 variant first detected in Brazil, as well as mutations from other emerging SARS-CoV-2 strains. "The flexibility of BioNTech's proprietary mRNA vaccine platform is well suited to develop new vaccine variants if required," they added.

Also published in the NEJM on Wednesday were previously reported data from a laboratory study showing that Moderna's coronavirus vaccine mRNA-1273 triggered roughly six times fewer neutralising antibody titres against B.1.351 relative to prior variants, although there was "no significant effect" on its ability to neutralise B.1.1.7 mutations. "Protection against the B.1.351 variant conferred by the mRNA-1273 vaccine remains to be determined," the authors said in the NEJM preliminary report.

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