LONDON (REUTERS) - AstraZeneca is to start clinical trials to test a combination of its experimental Covid-19 vaccine with Russia's Sputnik V shot to see if this can boost the efficacy of the British drugmaker's vaccine, Russia's sovereign wealth fund said on Friday (Dec 11).

Trials will start by the end of the year and Russia wants to produce the new vaccine jointly if it is proven to be effective, said the RDIF wealth fund, which has funded Sputnik V.

AstraZeneca said it was considering how it could assess combinations of different vaccines, and would soon begin exploring with Russia's Gamaleya Institute, which developed Sputnik V, whether two vaccines based on a common-cold virus could be successfully combined.

It did not give further details. However, its Russian arm said it would start to enrol adults aged 18 and older for the trial.

The cooperation between one of Britain's most valuable listed companies and the state-backed Russian research institute highlights the pressure to develop an effective shot to fight the pandemic, which has killed over 1.5 million people.

The move is likely to be seen in Moscow as a long-awaited vote of confidence by a Western manufacturer in Sputnik V, which the Russian defence ministry alleged on Friday was the target of a foreign-backed smear campaign.

Sputnik's Russian developers say clinical trials, still under way, have shown it has an efficacy rate of over 90 per cent, higher than that of AstraZeneca's own vaccine and similar to those of US rivals Pfizer and Moderna.

Some Western scientists have raised concerns about the speed at which Russia has worked, giving the regulatory go-ahead for its vaccines and launching large-scale vaccinations before full trials to test Sputnik V's safety and efficacy have been completed. Russia says the criticism is unfounded.

AstraZeneca, once seen as a frontrunner in the vaccine race, is preparing further tests to confirm whether its shot could be 90 per cent effective, potentially slowing its rollout.

Its average efficacy rate was 70.4 per cent in interim late-stage data - which prompted the developers of Sputnik V to suggest trying to combine the two vaccines.

Two vaccines better than one?

RDIF head Kirill Dmitriev called AstraZeneca's acceptance of the proposal "an important step towards uniting efforts in the fight against the pandemic".

Kate Bingham, chair of Britain's vaccine task force, said this week that the UK would start trials next year, using combinations of different kinds of vaccine for the initial and booster vaccinations, in the hope that a "mix-and-match" approach might maximise the immune response.

Both projects are using harmless adenoviruses as vehicles, or vectors, to carry genetic instructions into the body to prompt cells to produce antibodies, an approach that has previously been used in an Ebola vaccine.

One challenge of such a method is that the immune system could attack the vector and, in particular, neutralise the second booster shot that is now an important feature of the leading Covid-19 vaccine candidates.

Using different viral vectors for the two shots is one approach that researchers, including at the Gamaleya Institute, have pursued. Combining vaccines from different developers could be another.

AstraZeneca did not mention immunity against the viral vector as an issue in its statement on Friday.

The firm and its partner Oxford University have used a harmless adenovirus found only in monkeys to ensure that people receiving the shot had not previously been exposed to the vector and developed an immune response against it.

Russian officials have not always been complimentary about the British vaccine.

When AstraZeneca paused a clinical trial in September due to the unexplained illness of a volunteer, Kremlin spokesman Dmitry Peskov told reporters that Sputnik V was more reliable because it was based on an adenovirus found in humans, whereas the British candidate was a "monkey vaccine".

The new partnership may draw scrutiny after Britain said in July that hackers backed by the Russian state were trying to steal Covid-19 vaccine and treatment research from academic and pharmaceutical institutions around the world. The Kremlin rejected the allegations.