Two COVID-19 vaccines have prompted an antibody response in human study participants, an encouraging sign as clinical trials move forward, say observers.

Medical journal The Lancet on Monday published early results for the two candidates. One, a vaccine from AstraZeneca and the University of Oxford, triggered “strong” immune responses in a 1,000-participant study, according to the researchers. It also was determined to be safe, producing mild-to-moderate side effects in 60% of participants. Phase 3 trials are currently underway.

Likewise, a COVID-19 vaccine by Chinese drugmaker CanSino Biologics produced antibody responses without unsafe side effects in a phase 2 trial. 

The two vaccines use a harmless cold virus to carry genetic material from the novel coronavirus into the body, aiming to induce an immune response, according to Reuters.

“Overall, the results of both trials are broadly similar and promising,” wrote vaccine experts Naor Bar-Zeev, Ph.D., and William Moss, M.D., from Johns Hopkins Bloomberg School of Public Health, in a commentary accompanying the studies.

Meanwhile, Moderna and the National Institute of Allergy and Infectious Disease last week announced news of similarly promising vaccine trial results, and German firm BioNTech and vaccine development partner Pfizer have said they are confident their vaccines will be ready for federal approval by the end of this year. Pfizer had announced in May that the two companies already were scaling up production potential with an aim to rapidly make and distribute doses globally.