COVID-19: J&J’s Vaccine Candidate Registers Strong Immune Response in Early Trials

by Eduardo Longoria
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By Eduardo Longoria

Johnson & Johnson’s lead COVID-19 vaccine candidate, Janssen COVID-19 (JNJ-78436735), is a viral vector vaccine constructed from a modified adenovirus that carries the genetic instructions for SARS-CoV-2’s spike protein. Last week, the company published a preliminary analysis of the Phase 1/2a clinical trials on the medRxiv prepress server. The multicenter, randomized, double-blind, placebo-controlled study tested the safety, responsiveness, and immunogenicity (ability to induce an immune response) of the vaccine in two doses administered intramuscularly to healthy adults aged 18-55 and over 65 years in 8-week intervals.

Data showed that a dose of JNJ-78436735 induced an antibody neutralization response in almost all participants 18 years and older and is generally well tolerated across age groups, including the elderly. Seroconversion (development of detectable antibodies) was observed in 99% of participants aged 18-55. Immunogenicity data from 15 participants over the age of 65 also showed strong humoral and cellular immune responses observed in all older participants who were given a dose.

Preliminary safety data obtained during the study indicates that most of the adverse effects were mild to moderate (grades 1 and 2) in severity and usually happened on the day of vaccination with symptoms usually resolved within a day or two. Two unusual events were reported, the first of which was caused by hypotension, which the examiner considered unrelated to the vaccine. The second was a participant hospitalized as a result of fever with suspected COVID-19 but recovered in less than 12 hours. No unwanted 4th grade (life-threatening) events were reported, and none of the participants stopped the study. The analysis showed that there was a tendency to be more reactive to a higher dose of the vaccine in younger people as well as those who received higher doses. In clinical trials for vaccines, it is commonly understood that local and systemic side effects are common and temporary.

The interim analysis has also shown that a single dose of vaccine is sufficient to induce a reliable immune response. This data is consistent with preclinical studies published in the scientific journal Nature, which indicates that a single dose successfully prevents subsequent infection by the virus and provides full protection in the lungs of non-human primates. Based on these findings, the one-dose regimen was selected for further evaluation in ENSEMBLE Phase 3 clinical trials.

The ENSEMBLE Phase 3 trial intends to evaluate the safety and efficacy of the single-dose versus placebo in up to 60,000 adults over 18 years. The trial will include subjects with and without comorbidities associated with an increased risk for progression to severe COVID-19. It will aim to enroll participants throughout Latin America as well as South Africa and the United States. Depending on the outcome of the ENSEMBLE trial, the vaccine is predicted to be ready by the end of 2021 via an emergency use authorization (EUA) from the FDA.

Editor: Rajaneesh K. Gopinath, Ph.D.

Related Article: FDA Halts Another Coronavirus Vaccine Trial



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