Vaccines offer the best way to stop Covid-19, but they aren’t an option for people with weak immune systems or an intolerance to the components of these shots. The FDA has granted emergency authorization to a long-acting AstraZeneca drug that can give these patients a protective measure.
The AstraZeneca drug is an antibody therapy, and it joins a growing list of antibody drugs that have cleared the FDA bar for emergency use. But the drug, Evusheld, does mark one new first for antibody treatments: It’s the first authorized for use as a way to prevent the disease before an individual has been exposed to the virus. The other antibody drugs whose authorizations include Covid-19 prevention may only be used to treat those who have already been exposed to someone with the virus.
Evusheld’s authorization covers use of the drug in adults, as well as children who are 12 and older who weigh at least 40 kilograms (about 88 pounds). Those individuals must have weakened immune systems due to a medical condition or immunosuppressive medications. The drug may also be used by patients who have a history of bad reactions to components of Covid-19 vaccines.
AstraZeneca tested its drug in a placebo-controlled Phase 3 study enrolling nearly 5,200 adults 59 and older. Those trial participants had medical condition that made them likely to be poor responders to vaccines or otherwise intolerant of them. Also, trial participants did not have a history of prior SARS-CoV-2 infection, nor did they test positive for infection at the start of the study.
The main goal of the pivotal study was to see whether participants developed Covid-19 after receiving the study drug or a placebo. In August, AstraZeneca reported a primary analysis showing that those given Evusheld had a 77% reduced risk of developing Covid-19 compared to those who received a placebo.
Evusheld is a combination of two monoclonal antibodies, tixagevimab and cilgavimab. Those antibodies, derived from B cells of patients recovering from SARS-CoV-2 infection, were discovered by scientists at Vanderbilt University. AstraZeneca licensed the rights to them last year. Evusheld is given as two separate intramuscular injections given one after the other. Like other Covid-19 antibody drugs, Evusheld is designed to target the spike protein of SARS-CoV-2, blocking its ability to attach to and enter into human cells. Also, like other antibody combination treatments, the two antibodies that comprise Evusheld bind to different sites of the spike protein, reducing the chance that a mutation makes the virus resistant to the therapy.
One key differentiator of Evusheld could be its durability. AstraZeneca applied proprietary technology to the two Vanderbilt antibodies that extends their half-lives, enabling them to last for potentially as long as one year. In the clinical trial results so far, the 77% reduction in the risk of developing Covid-19 was maintained in the Evusheld group through six months. AstraZeneca said additional follow-up is needed to assess how long the drug’s benefit lasts.
The list of FDA authorized antibody treatments include drugs from Eli Lilly, Regeneron Pharmaceuticals, and partners Vir Biotechnology and GlaxoSmithKline. The antibody combination drugs from Lilly and Regeneron have authorizations for treating mild-to-moderate Covid-19 cases, as well as for prevention of disease in patients who have been exposed to the virus. Prophylactic use of both antibody drugs covers those who are not fully vaccinated or whose weakened immune systems are not likely to generate an adequate response. Last week, the FDA expanded emergency use of Lilly’s antibody combination to include children younger than 12, including infants, making it the first authorized Covid-19 therapy for this younger age group.
AstraZeneca is still running tests to assess how the new omicron variant affects Evusheld. The company said that in animal testing so far, none of the viral changes have been associated with the ability of the virus to escape neutralization by Evusheld. In lab tests, AstraZeneca said its drug is able to neutralize other variants, including the delta and mu variants.
Evusheld is being developed with support from the U.S. government. AstraZeneca has agreed to supply the government with 700,000 doses for distribution to all U.S. states and territories. The company said it expects the first doses of its new Covid-19 drug will become available “very soon.”
Photo by AstraZeneca