On 11 August, the Russian Direct Investment Fund (RDIF), which markets the Russian vaccine abroad, proposed to US drugmaker Pfizer to start joint trials with Sputnik Light as a booster third shot.
"The move by the RDIF to propose Pfizer boosting with Sputnik Light is quite reasonable, those who are vaccinated with Pfizer could be better protected by a wide range of antibodies which they will generate after the boost," Gintsburg said.
Pfizer efficacy against the Delta variant is still unclear.
Sputnik V efficacy against the Delta variant was estimated by the Russian Health Ministry at 83.1%. Meanwhile, Pfizer efficacy against COVID-19 dropped in July when the Delta variant became dominant, according to a report, published on MedRxiv, a website server distributing e-prints in the health sciences still not reviewed by peers. It estimated the Moderna vaccine efficacy against the Delta strain at 76% and Pfizer at 42%.
The single-dose Sputnik Light vaccine was registered early in May in Russia, with its efficacy at 79.4%. Sputnik Light is the first Sputnik V component, with no severe side effects.