Single-Dose Treatment of Covid-19 with Pegylated Interferon Lambda

The February 9th issue of The New England Journal of Medicine includes an article on a randomized controlled trial of a new antiviral treatment for Covid-19.1 Interferon lambda (IL-28 and -29) is an antiviral protein that has a protective effect at epithelial surfaces.2 It has been studied for antiviral activity against SARS-CoV-2 and in two phase 2 trials in patients with Covid-19, but it is not available commercially in the US.

This trial was conducted in Brazil and Canada in mostly (83%) vaccinated patients with a positive rapid antigen test within 7 days after the onset of Covid-19 symptoms. The patients received a single injection of 180 micrograms of pegylated interferon lambda or an appropriate placebo.

The primary outcome, Covid-related hospitalization or an emergency-room visit of at least 6 hours within 28 days after randomization, occurred in 25 of 931 patients (2.7%) who received interferon lambda and 57 of 1018 (5.6%) who received placebo, a 51% decrease. Treatment benefits occurred across all variants, but the greatest risk reduction appeared to be with the Omicron variant. There were 4 Covid-related deaths with placebo and none with interferon lambda. There was no substantial difference in adverse events.

Among the patients who received interferon lambda or placebo within 3 days after the onset of symptoms, the decrease in the primary endpoint with interferon lambda was 58%. Among unvaccinated patients who were treated within 3 days, the risk reduction was 89%.

When, if ever, pegylated interferon lambda will become available in the US is unclear. Paxlovid remains the drug of choice here for antiviral treatment of Covid-19.

  1. G Reis et al. Early treatment with pegylated interferon lambda for COVID-19. N Engl J Med 2023; 388:518. doi:10.1056/NEJMoa2209760
  2. HM Lazear et al. Interferon-λ: immune functions at barrier surfaces and beyond. Immunity 2015; 43:15. doi:10.1016/j.immuni.2015.07.001

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