In a study published in the journal Clinical Infectious Diseases, a Johns Hopkins Medicine research team reports that for XBB.1.5, there is good news for solid organ transplant recipients (SOTRs) and other immunocompromised people who receive regular booster doses of a messenger RNA (mRNA) bivalent vaccine (a vaccine designed to enhance immunity to a variety of SARS-CoV-2 strains).
The researchers studied 76 SOTRs who had received a minimum of three doses of a primary monovalent (active against just the original SARS-CoV-2 strain) mRNA vaccine, reported receiving either one or two bivalent mRNA vaccine boosters (containing both the original strain and the omicron BA.5 variant), and provided two or more blood samples that were obtained pre- and post-bivalent booster in one of three groups: 59 paired samples taken before and after the first booster, 31 paired samples taken before and after the second booster, and 14 paired samples taken before and after both boosters.
The study participants were generally middle age, more than five years post-transplant, and were kidney and/or liver transplant recipients. Fourteen had evidence of COVID-19 before the first booster, while 16 developed COVID-19 between the first booster and one month past the second.
The researchers found that the amount of circulating antibody and, in turn, virus neutralization, significantly increased by one month after the first bivalent booster for both the BA.5 and XBB.1.5 strains of SARS-CoV-2. However, this dropped sharply to nearly the pre-booster levels at three months, and even more so at six months.
Following a second bivalent booster, many SOTRs regained the ability to neutralize both virus strains; yet 42% did not have any detectable immunity to XBB.1.5. The researchers found that those SOTRs were more likely to be receiving corticosteroids as part of a three-drug immunosuppression regimen. They also discovered that, at nearly all times post-vaccinations (monovalent plus bivalent boosters), SOTRs with no prior SARS-CoV-2 infection showed poor XBB.1.5 neutralization, and at levels far below those who had hybrid (infection and vaccination) immunity.
