By Deena Beasley

(Reuters) – As Merck & Co and Pfizer Inc (NYSE:) prepare to report clinical trial results for experimental COVID-19 antiviral pills, rivals are lining up with what they hope will prove to be more potent and convenient oral treatments of their own.

Enanta Pharmaceuticals (NASDAQ:), Pardes Biosciences, Japan’s Shionogi & Co Ltd and Novartis AG said they have designed antivirals that specifically target the coronavirus while aiming to avoid potential shortcomings such as the need for multiple pills per day or known safety issues.

Experts in infectious diseases stressed the importance of preventing COVID-19 by wide-ranging vaccinations. They said that the disease will not go away and they need to find more effective treatments.

We need oral options to suppress this virus. “We have people getting sick from vaccines that aren’t working,” Dr. Robert Schooley said. He is an infectious diseases professor at UC San Diego School of Medicine.

Pfizer, Merck, and Atea Pharmaceuticals along with Roche AG and Roche AG said that they may be eligible for emergency approval to use their COVID-19 antiviral medication this year.

Rivals are currently at least one year behind. Pardes has started an early stage trial, Shionogi is planning to launch large-scale clinical studies by the end of this year, Enanta hopes to open human trials soon next year, and Novartis still tests its pills in animals.

Jay Luly, Enanta’s Chief Executive said it is possible to repurpose drugs that were originally made for other viral diseases. However, it’s not clear how powerful they will be in fighting COVID-19. It also isn’t known how they can reach lung tissue where the virus takes root.

Luly warned that “if it isn’t a big effort…you will end up losing your time.”

Because they target the virus once it has already replicated inside cells, antivirals can be difficult to create. They must not damage healthy cells. To be effective, they must be administered early.

For non-hospitalized COVID-19 sufferers, only intravenous or injected antibody treatments are currently approved.

An effective, convenient COVID-19 treatment could reach annual sales of over $10 billion, according to a recent Jefferies (NYSE:) & Co estimate. Merck signed a deal with the U.S. government for $700 per course of antiviral medication molnupiravir.

SEARCH FOR AN EASY TREATMENT

Several classes of antiviral drugs are being explored. Atea’s antiviral drug, a polymerase inhibitor originally developed to treat hepatitis C, is intended to block the coronavirus’ ability to create copies of its own. Pfizer’s Pill is a protease inhibitor that blocks an enzyme needed by the virus to grow earlier in its lifecycle.

Pardes’ CEO Uri Lopin stated that they are working to stop “the virus from setting up a replication facility”.

Merck’s molnupiravir was originally developed in collaboration with Ridgeback Therapeutics. It works by introducing mistakes into the virus’ genetic code.

Jay Grobler oversees Merck’s vaccines and infectious diseases. He said that molnupiravir has a broad range of activity against all RNA viruses.

Merck stated that data from the trial showed the drug was not capable of inducing any genetic changes in human cell cells. Men in it must either abstain heterosexually or consent to contraception.

Nicholas Kartsonis, Merck’s research executive said that until reproductive toxicology results have been published, it is not possible to determine if the drug has any effect on sperm.

Pfizer’s pills and molnupiravir are both taken once a day for five days. Pfizer’s pill must be taken with an older antiviral drug ritonavir. This increases the activity of protease inhibitors, but may cause side effects or interfere with other medication.

Schooley explained that adding a drug to a prescription is an inconvenience.

Pfizer stated that a lower dose of ritonavir would allow its protease inhibitor to remain longer in the body and at greater concentrations.

Enanta, which gets most of its revenue from a hepatitis C deal with AbbVie Inc (NYSE:), scanned its library of antiviral compounds early in 2020. Instead, it decided to create a protease inhibitor to target an enzyme that is vital for the coronavirus and all its variants to reproduce.

Luly indicated that this drug will only be used once per day and with no ritonavir-boosting.

Lopatin stated that Pardes will be evaluating once- or twice-a day dosing, and whether the drug should be mixed with ritonavir. His statement said, “We don’t anticipate that we would need to use booster.”

Pardes was funded by Gilead Sciences, NASDAQ:. The company has given up on the inhalation version of its intravenous polymerase inhibitor remdesivir.

Gilead continues to work on an oral version of remdesivir that was first created for hepatitis C. It is the current only approved antiviral for COVID-19.