A merger of drugmakers AstraZeneca and Gilead Sciences is unlikely, said analysts, after reports said the UK firm made a preliminary approach to its US peer last month.

Political opposition from both the UK and the US could derail any attempt at a deal, especially given the backdrop of the Covid-19 outbreak, Citigroup said.

“US government would likely try to block any acquisition of a major US biopharma company that is involved in pandemic therapeutic development. Even greater political opposition is seen from the UK government,” wrote Citigroup analyst Andrew Baum.

The timing is also questionable, as while Gilead is in the middle of a turnaround, AstraZeneca is well positioned and has a strong pipeline, analysts said. Yet there is potential for synergies, and Gilead could compliment AstraZeneca’s portfolio in the areas of virology and inflammatory treatment, according to RBC. AstraZeneca shares fell over 3 per cent in London, underperforming the Stoxx 600 Health Care Index. Gilead rose 4.6 per cent in premarket trading.

AstraZeneca, co-developer of one of the fastest-moving experimental coronavirus vaccines, has made a preliminary approach to Gilead Sciences, maker of the only US-approved treatment, according to people familiar with the matter. If they decided to pursue a merger, it would rank as the biggest deal ever in the sector.

The companies aren’t in formal discussions, according to the people, and some investors expressed scepticism about the strategic rationale. Still, the mere suggestion of a blockbuster pharma merger is a sign that the industry is getting back to something resembling business as usual. Successful Covid-19 treatments or vaccines are unlikely to be big moneymakers, meaning drugmakers face the return of old pressures to gain scale and boost innovation, or risk becoming targets.

AstraZeneca Chief Executive Officer Pascal Soriot learned that lesson six years ago when Pfizer launched an unsuccessful bid for the UK company that eventually reached $117 billion in value.

Now, Soriot can ponder a deal that would insulate the company against takeovers, making it one of the world’s biggest drugmakers.