Using the Johnson & Johnson vaccine as a booster for people initially immunized with the Pfizer/BioNTech vaccine produces a strong immune response and may do more to elicit protection against severe disease, researchers reported Sunday.Their small study of 65 volunteers who all initially got two doses of Pfizer/BioNTech's vaccine showed that using the J&J Janssen vaccine as a booster produced a slower but more sustained antibody response against the original strain of the virus, as well as the Delta and Beta variants, they said.The Pfizer/BioNTech booster produced a quicker and stronger immune response that dropped off faster, their study suggested."Both vaccines boost antibody titers very well. At week four, neutralizing antibody levels were comparable," Dr. Dan Barouch of Beth Israel Deaconess Medical Center and Harvard Medical School, who led the study team, told CNN.But after four weeks, antibody levels began to drop off in people who got boosted with the Pfizer vaccine while they continued to increase in people who got J&J's vaccine. J&J's vaccine also increased the numbers of immune cells called CD8 T cells.Antibodies are a first line of immune protection that can stop a virus from ever infecting cells, while T cells come in later and destroy infected cells. This T-cell defense doesn't prevent mild infections, but can stop them from progressing to severe disease.While the study did not include the omicron variant, Barouch said the findings may be important for coming up with ways to fight the latest variant."For variants such as omicron that might partially evade antibody responses, CD8 T cell responses may be particularly relevant for protection," he said. "We think they're relevant in general but they may become particularly relevant if a variant emerges that can largely escape from antibodies.""Now we don't know that for sure yet about omicron, but as I'm sure you know, there's been a lot of concern or speculation that it might result in at least some degree, maybe a substantial degree, of escape from vaccine induced antibodies. For a boost, you do want a boost to increase both antibody and T-cell responses."Barouch said his team has submitted the findings to a peer-reviewed journal and in the meantime it has been posted online, without peer review, on the preprint server MedRxiv.