As doctors scramble to contain the fast-spreading coronavirus, a potent brew of anti-retroviral and flu drugs has emerged as a possible defence against the disease that has killed hundreds.

But the science is inconclusive on whether they are actually effective, and experts say a specific treatment could take years to develop.

Here is what we know — and don’t know — about the drugs deployed against the SARS-like virus. Patients diagnosed with the common flu are often prescribed an antiviral drug widely known as Tamiflu. But seasonal flu is “very different from the Chinese coronavirus”, said Sylvie van der Werf at the Paris-based Pasteur Institute.

So far the new coronavirus has infected tens of thousands worldwide and killed more than 420 people, mostly in mainland China.

Two weeks ago Chinese doctors confirmed they had been giving anti-HIV drugs to coronavirus patients in Beijing, based on a 2004 study published after the outbreak of Severe Acute Respiratory Syndrome (SARS) that showed “favourable” responses.

Used together, lopinavir and ritonavir decrease the amount of HIV cells in a patient’s blood, stripping back the virus’s ability to reproduce and attack the immune system.

Doctors have also combined the treatment with another anti-flu drug called oseltamivir, hoping the creative cocktail can sap the new coronavirus of its strength. In Thailand, where there are now 25 confirmed cases, a 71-year-old Chinese patient returned a negative test within 48 hours of being given the three drugs. But Thai doctors urged caution, saying the medicine needed to be given under supervision due to possible side effects. In short, we don’t know for sure.

The 2004 study showed anti-retrovirals used on patients with SARS had “substantial clinical benefits”, experts in China said. But random trials on 41 coronavirus patients had “limitations”, according to research published in The Lancet on January 24.

Meanwhile, the World Health Organisation said on Tuesday that the outbreak of coronavirus does not yet constitute a “pandemic”.