As booster campaigns against COVID-19 across the world are ramped up to combat a new wave of Delta variant and the threat of the new Omicron variant, data is trickling in on the effectiveness of a mix-and-match approach.
Johnson & Johnson (J&J) has released preliminary results from a small phase 2 study that show a booster shot of its COVID-19 vaccine, Ad26.COV2.S, not only elicits a ‘substantial increase in antibody and T-cell responses’ but that the protection may be greater than a booster with Pfizer/BioNTech’s Comirnaty.
In the study, conducted at the Beth Israel Deaconess Medical Center (BIDMC) in Boston, 65 people who had previously received Comirnaty were given either a third, booster shot of Pfizer/BioNTech’s vaccine or a shot of J&J’s vaccine six months after the primary regimen.
“There is early evidence to suggest that a mix-and-match boosting approach may provide individuals with different immune responses against COVID-19 than a homologous boosting approach,” said Dr Dan Barouch, director of the Center for Virology and Vaccine Research at BIDMC.
“In this preliminary study… there was a comparable increase of antibody responses at week four following the boost and a greater increase of CD8+ T-cell responses with Ad26.COV2.S compared with BNT162b2,” he said.
These phase 2 data align with preliminary results from the UK’s COV-BOOST study published in The Lancet last week which found that ‘all study vaccines boosted antibody and neutralising responses’ following an initial course of the Oxford/AstraZeneca vaccine, sold under the name Covishield or Vaxzevria.
However, the authors noted that “substantial differences in humoral and cellular responses” would “influence policy choices for booster vaccination”.
In the J&J-funded study in Boston, humoral (antibody) responses for a booster of Ad26.COV2.S led to a similar level of neutralising and binding antibodies against the original SARS-CoV-2 strain and both the Delta and Beta variants four weeks following the boost.
However, with a J&J booster dose, antibodies continued to increase for at least four weeks whereas antibodies declined from week two to week four following a booster with Comirnaty.
With cellular (T-cell) responses, its vaccine “appears to lead to a greater increase in CD8+ T-cell responses than boosting with BNT162b2”, said J&J.
“These T-cell response data suggest differences between immune responses following homologous boosting with BNT162b2 and mix-and-match boosting with the Johnson & Johnson COVID-19 vaccine following a primary regimen of BNT162b2,” J&J added.