Covid pill works against all variants including Delta, manufacturer says

But Merck & Co says its experimental oral Covid-19 antiviral drug is most effective when given early in course of infection

File photo: Merck says molnupiravir is effective against all strains of the coronavirus, including the dominant Delta variant (AP)

Drugmaker Merck & Co’s experimental oral Covid-19 antiviral drug is effective against all known variants of the virus, the company said on Wednesday.

Laboratory studies have shown that molnupiravir is effective against all strains of the coronavirus, including the dominant Delta variant, Merck said. But it added that the drug is most effective when given early in the course of infection.

“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 targets the viral polymerase, an enzyme needed for the virus to make copies of itself, the company said. It is designed to work by introducing errors into the genetic code of the virus, Merck said.

Merck tested its antiviral drug against nasal swab samples taken from patients who were in the early stages of drug trials.

The latest data analysis was presented during Infectious Disease Week, the annual meeting of all infectious disease organisations in America.

Merck said earlier this year that a small, mid-stage trial found that after five days of molnupiravir treatment, none of the patients taking various doses of the drug tested positive for the virus, while 24 per cent of placebo patients had detectable levels of the virus.

Merck is currently conducting two Phase III trials of the antiviral it is developing with Ridgeback Biotherapeutics — one to treat Covid-19 and another to prevent it.

The trial enrolled non-hospitalised Covid-19 patients who have had symptoms for no more than five days and are at risk for severe disease. The Phase III treatment study is expected to finish in early November, Mr Grobler said.

“Oral antivirals have the potential to not only curtail the duration of one’s Covid-19 syndrome but also have the potential to limit transmission to people in your household if you are sick,” Timothy Sheahan, a virologist at the University of North Carolina-Chapel Hill, told NBC News.

Carl Dieffenbach, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases, said that at least three “promising” antivirals for Covid-19 were currently being tested, and the results of these are expected in the winter. While one is Merck’s molnupiravir, the two others are manufactured by Roche and Atea Pharmaceuticals, and Pfizer, he said.