A small preliminary laboratory study has shown that levels of Omicron-neutralising antibodies of people vaccinated with Russia's Sputnik V vaccine did not decline as much as of those who had Pfizer shots.

The joint Russian-Italian study - funded by the Russian Direct Investment Fund, which markets Sputnik V abroad - compared the blood serum of people who had received the different vaccines.

The preliminary study was conducted by scientists from the Spallanzani Institute in Italy and Gamaleya Institute in Moscow, the developer of Sputnik V vaccine.

Researchers said samples taken three to six months...