By Jim Williams

CHICAGO (CBS) — More than 100, Chicagoans have already rolled up their sleeves for the Johnson & Johnson one dose vaccine.

But Chicago researchers are injecting some people with two shots of the J & J vaccine for a clinical trial. CBS 2’s Jim Williams reports on whether this will me the end of the single shot vaccine.

READ MORE: Opening Statements Begin In Jussie Smollett Trial

In January, Jack Sheehan got a text from a friend. Perhaps he’d like to participate in a COVID vaccine clinical trial in the North Side’s Andersonville community.

It sounded appealing.

“Because in our age, we knew it wouldn’t be until May.”

Better to get the shot sooner rather later, he thought. And so Sheehan agreed to help test the Johnson & Johnson vaccine. In this trial, Sheehan would get two shots of the Johnson & Johnson vaccine.

“I knew from the onset I would be getting two shots.”

READ MORE: Officials Seek To Quell Fears Over New Omicron COVID-19 Variant As Concerns And Questions Grow; 'There Is No Reason For Panicking'

It might sound confusing, because the Johnson & Johnson vaccine is only a single shot, unlike the Pfizer and Moderna vaccines which require two shots.

Researchers are testing whether a second shot of the Johnson & Johnson offers even more protection against COVID. Clinical trials showed the Johnson & Johnson one-shot vaccine was 72 effective in the United States

It’s given 43 to 57 days after first Johnson & Johnson shot. The second Pfizer and Moderna doses are administered 21 days apart. What was Jack Sheehan told about the time gap?

“They told this one wouldn’t be like Pfizer and Moderna because this one is a booster.”

Sheehan had his second Johnson & Johnson shot in March. He said he was a bit lethargic after each shot, but he feels good now and even took a vacation out of town. Sheehan was pleased he participated in the trial.

“I hope good comes of it,” Sheehan said. “And the immunity will last longer and we can get over this sooner than later.”

MORE NEWS: 17-Year-Old Boy Killed, 4 Injured In Evanston Shooting; Police Believe Shooting Was Targeted

Jack Sheehan said he was told the trial will take two years and he uses an app on his phone to provide updates on his health.