Currently approved viral vector-based and mRNA-based vaccine approaches against coronavirus disease 2019 (COVID-19) consider only homologous prime-boost vaccination. After reports of thromboembolic events, several European governments recommended using AstraZeneca’s ChAdOx1-nCov-19 (ChAd) only in individuals older than 60 years, leaving millions of already ChAd-primed individuals with the decision to receive either a second shot of ChAd or a heterologous boost with mRNA-based vaccines. However, such combinations have not been tested so far. We used Hannover Medical School’s COVID-19 Contact Study cohort of healthcare professionals to monitor ChAd-primed immune responses before and 3 weeks after booster with ChAd (n = 32) or BioNTech/Pfizer’s BNT162b2 (n = 55). Although both vaccines boosted prime-induced immunity, BNT162b2 induced significantly higher frequencies of spike-specific CD4⁺ and CD8⁺ T cells and, in particular, high titers of neutralizing antibodies against the B.1.1.7, B.1.351 and P.1 variants of concern of severe acute respiratory syndrome coronavirus 2.

Objectives: People living with HIV (PLWH) with low CD4 T‐cell counts may be at a higher risk for severe coronavirus disease 2019 (COVID‐19) outcomes and in need of efficient vaccination. The World Health Organization (WHO) now recommends prioritizing PLHIV for COVID‐19 vaccination. Data on immune responses after messenger RNA (mRNA) vaccination in PLHIV in relation to CD4 counts are scarce. We aimed at assessing the humoral immune response in PLHIV after mRNA vaccination against COVID‐19.Methods: We examined a cohort of PLHIV after prime (n = 88) and boost (n = 52) vaccination with BNT162b2. We assessed levels of anti‐severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) spike (S) protein‐specific immunoglobulin G (IgG)/IgA and circulating neutralizing antibodies in plasma and correlated results to the cellular immune status. BNT162b2‐vaccinated health care workers served as controls.Results: All PLWH had a viral load of ≤ 200 HIV‐1 RNA copies/mL and 96.5% had a viral load of < 50 copies/mL. Anti‐S IgG and neutralizing antibody responses after BNT162b2 priming were significantly lower in PLHIV having a CD4:CD8 T‐cell ratio of < 0.5. However, we observed robust humoral immunity in the majority of PLWH receiving antiretroviral therapy (ART) irrespective of CD4 T‐cell nadir, current CD4 count or CD4:CD8 ratio after full BNT162b2 vaccination. Nevertheless, HIV‐negative controls produced significantly higher mean anti‐S IgG concentrations with less variability.Conclusions: The majority of PLWH mounted robust responses after complete BNT162b2 vaccination but overall amounts of antibodies directed against the SARS‐CoV‐2 receptor‐binding domain were variable. The impact on clinical efficacy remains unclear.

Heterologous prime/boost vaccination with a vector-based approach (ChAdOx-1nCov-19, ChAd) followed by an mRNA vaccine (e.g. BNT162b2, BNT) has been reported to be superior in inducing protective immunity compared to repeated application of the same vaccine. However, data comparing immunity decline after homologous and heterologous vaccination as well as effects of a third vaccine application after heterologous ChAd/BNT vaccination are lacking. Here we show longitudinal monitoring of ChAd/ChAd (n = 41) and ChAd/BNT (n = 88) vaccinated individuals and the impact of a third vaccination with BNT. The third vaccination greatly augments waning anti-spike IgG but results in only moderate increase in spike-specific CD4 + and CD8 + T cell numbers in both groups, compared to cell frequencies already present after the second vaccination in the ChAd/BNT group. More importantly, the third vaccination efficiently restores neutralizing antibody responses against the Alpha, Beta, Gamma, and Delta variants of the virus, but neutralizing activity against the B.1.1.529 (Omicron) variant remains severely impaired. In summary, inferior SARS-CoV-2 specific immune responses following homologous ChAd/ChAd vaccination can be compensated by heterologous BNT vaccination, which might influence the choice of vaccine type for subsequent vaccination boosts.