But antibody therapies have drawbacks. They are expensive and must be given by infusion or injection. This makes them poor choices for many low- and middle-income countries. And they may not perform well against some of the traded variables. In fact, on June 25, the Food and Drug Administration halted the nationwide distribution of a nighttime cocktail of antibodies across the country due to the increasing prevalence of two different types of anxiety that do not appear to respond to the drugs.
When it comes to antiviral drugs, which hamper the virus’s ability to multiply, fewer options are available. Remdesivir is the only drug approved to treat Covid-19, in large part because it was one of the few candidates tested for safety in humans when the pandemic spread, so it had a head start. But how successful it will be is still an open question. Some studies have found that it shortens the duration of illness, while others suggest it has little effect. The World Health Organization does not recommend its use.
The development of antivirals has been delayed for several reasons. Until COVID-19, companies didn’t have much financial incentive to produce these drugs. Existing antivirals target only 10 viruses, and half of them treat HIV. Chronic infections require longer treatments and therefore you earn more money. “If there is no clear market for a curative treatment, they are not going to invest in those types of treatments,” says John Bamforth, interim executive director of READDI, a public-private partnership at the University of the North. Carolina at Chapel Hill was founded to develop new antivirals.
There are also a number of scientific hurdles. To prevent replication, the drug binds to some essential viral protein or enzyme and blocks its activity without harming the host cell. But unlike bacteria, viruses rely on the machinery inside the cells they live in to copy themselves, so they have very few proteins of their own. And even when researchers come across a potent compound, its efficacy tends to be short-lived because viruses are constantly evolving.
Some researchers, including those at READDI, are working on drugs that target cellular proteins essential for virus replication. Most antiviruses only work on one virus. We hope these compounds will be effective against entire families. They may also be less likely to lead a resistance.
But new treatments take longer to develop. That’s why the quickest way to get drugs off the shelves is to reuse compounds that have already been approved. They’ve been tested for safety, and there are fewer regulatory hurdles to getting new approval for an existing drug. DNDi is testing a variety of compounds found in a clinical trial called ANTI-COV. The most recent study is looking at the antiparasitic drug nitazoxanide with an inhaled steroid. “The consensus that is starting to emerge is that you will need a strong antiviral or a combination of antivirals with different mechanisms of action, along with some type of anti-inflammatories,” Cohen says.