Following BvB2, %ACE2 inhibition against XBB15 improved from 15% pre-boost to 28% post-boost, though achieving neutralizing inhibition remained a challenge for 42% of participants.
“We determined that for XBB15, neutralization levels waned by 3 months such that they were no different than before the bivalent boost. This was restored with a second boost, but did not improve the response beyond what was seen with the first boost,” explains Karaba.
3 Key Takeaways
- Initial bivalent mRNA vaccine boosters in SOTRs provided temporary neutralization against SARS-CoV-2 variants BA4/5 and XBB15, but these responses significantly declined by 3 months post-boost.
- 42% of participants did not achieve adequate neutralizing inhibition against the XBB15 variant, despite restoration of neutralization levels with subsequent boosters. This highlights the variability in vaccine response among different SARS-CoV-2 variants.
- Participants with hybrid immunity (before SARS-CoV-2 infection) exhibited higher overall neutralization of the XBB15 variant and maintained neutralization beyond 3 months post-bivalent boost, suggesting potential flexibility in booster timing based on infection history.
Participants received a minimum 3-dose primary monovalent vaccine series followed by bivalent mRNA vaccine boosters. Blood samples were collected at regular intervals post-boosts, and %ACE2 inhibition was assessed using MSD assays. Statistical analyses included Wilcoxon rank-sum, Fisher exact, and longitudinal modeling using R and Stata. This study was conducted between June 2022 and June 2023.
Hybrid immunity, facilitated by repeated boosters, enhanced both the peak level and duration of neutralizing antibodies against coronavirus variants. However, responses varied significantly between different variants, with notable differences observed in the efficacy against XBB.1.5 post-BvB1 and BvB2.
The study's limitations include the observational nature and relatively small sample size, limiting the generalizability of findings. Additionally, the study focused on humoral vaccine responses and did not evaluate T-cell responses or live virus-neutralizing antibodies.
Karaba continues, “Those with hybrid immunity (evidence of previous SARS-CoV-2 infection) had higher overall neutralization of XBB15. Furthermore, those with hybrid immunity-maintained neutralization beyond 3 months post-bivalent boost. So, while overall our findings suggest that frequent (every 3-6 months) may be necessary to maintain neutralizing antibody levels in transplant patients against emerging variants, those that had a relatively recent infection may be OK to get boosters closer to the 6-month part of that range, and getting a booster within 3 months of a recent infection is likely unnecessary.”
In conclusion, this study underscores SOTRs in maintaining robust immune responses against evolving SARS-CoV-2 variants post-vaccination. Regular boosting every 6 months should sustain effective neutralization, highlighting the ongoing need for tailored vaccination strategies in this high-risk population.
References
