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International group of researchers call Russian COVID-19 vaccine data into question

Sep 9, 2020 | 1:28 AM GMT

As researchers cast doubt on the Phase I/II data backing Russian COVID-19 vaccine Sputnik V, the degree to which preexisting antivector immunity dampens vaccine-induced immune responses remains an open question.

Sputnik V comprises an adenovirus serotype 5 (Ad5) vector and an adenovirus serotype 26 (Ad26) vector, each encoding the full-length SARS-CoV-2 spike and each delivered once in separate immunizations.

N.F. Gamaleya Scientific Research Institute of Epidemiology and Microbiology, which is run by the Russian Ministry of Health, published in The Lancet on Friday readouts from two Phase I/II trials that had been the basis of Russia’s Aug. 11 approval of Sputnik V. The vaccine is in a Russian Phase III trial enrolling 40,000 subjects (see “Russia Readies Phase III Study of ‘Sputnik’”; “Russian COVID-19 Vaccine Induces T Cell Responses, Antibodies”).

On Monday, 20 scientists from 19 institutions across the globe published an open letter questioning the reliability of the reported Phase I/II immunogenicity data. They cited “apparent duplications” — mostly in data from the Phase I participants — in depicting humoral and cellular immune responses, and called for the disclosure of the underlying numerical and cell sorting data to aid evaluation.

Gamaleya’s two-vector approach had been designed to avoid potential issues from amplifying antivector immunity, including suppression of boost-induced responses. The Gamaleya team had reported no significant correlation between preexisting antivector neutralizing antibody titers and vaccine-induced neutralizing titers against SARS-CoV-2 across individuals receiving only one Sputnik V component in the Phase I portions of the studies, or both components in Phase II. 

Those findings countered concerns raised in May by Phase I data from CanSino Biologics Inc. (HKEX:6185; Shanghai:688185) suggesting that high levels of preexisting antivector immunity dampens immunogenicity.

CanSino had reported in The Lancet a significant correlation between preexisting high anti-Ad5 titers and low anti-SARS-CoV-2 neutralization titers induced by Ad5-nCov, an Ad5 vector vaccine. Whether and the degree to which the lower titers indicate less protection remains unknown.

At least one other group has a human adenoviral vector COVID-19 vaccine in the clinic: Johnson & Johnson (NYSE:JNJ), which has yet to report human data. The pharma’s Ad26.COV2.S is an Ad26 vector vaccine.

J&J and CanSino are both are testing single and prime-boost regimens of their vaccines.

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