According to a study posted online Friday, Johnson & Johnson’s experimental Covid-19 vaccine-induced immune responses in most people who received the shot in a small early-stage trial also displayed an acceptable safety profile.

The findings added more detail to J&J’s announcement earlier this week that the results from the Phase 1/2 trial were positive, and mean the vaccine, one of the leading candidates in development, has taken another step toward proving whether it works safely.

According to the company, the results supported J&J’s decision to start a larger late-stage study of up to 60,000 people that will provide more definitive evidence of whether the vaccine safely protects people from Covid-19.

The large Phase 3 study could yield initial results by the end of the year or early 2021. If they are positive, the company said it would seek government authorization of emergency use.

J&J, of New Brunswick, N.J., started the first human study of its vaccine, code-named Ad26. COV2. S, in July in Belgium and the U.S., with a target of enrolling more than 1,000 adults.

Various dose levels and dosing regimens were tested on the study subjects.

Detailed interim results from the study were posted on the online preprint server medRxiv. The site publishes medical manuscripts before they are vetted by peer reviewers and published in medical journals.

Among the vast majority of specific subgroups of trial subjects, the study said, a single dose of the vaccine-induced so-called neutralizing antibodies to the coronavirus when measured in blood samples about four weeks after vaccination.

Neutralizing antibodies are agents of the immune system that researchers believe can block the virus and ward off Covid-19.

The concentrations of neutralizing antibodies induced by the vaccine were comparable to levels seen in the blood of people who had recovered from Covid-19, the study said. The neutralizing antibody responses among those vaccinated were comparable between younger adults and older adults, it said.

The early-stage study didn’t, however, show whether these immune responses prevented Covid-19. That will be tested in the new, larger study.