Laboratory studies show that Merck & Co's experimental oral Covid-19 antiviral drug, molnupiravir, is likely to be effective against known variants of the coronavirus, including the dominant, highly transmissible Delta, the company said.

Since molnupiravir does not target the spike protein of the virus — the target of all current Covid-19 vaccines — which defines the differences between the variants, the drug should be equally effective as the virus continues to evolve, said Jay Grobler, head of infectious disease and vaccines at Merck.

Molnupiravir instead targets the viral polymerase, an enzyme needed for the virus to make copies of itself. It is designed to work by introducing errors into the genetic code of the virus, Reuters reported.

Data show that the drug is most effective when given early in the course of infection, Merck said.