Even as the coronavirus disease 2019 (COVID-19) pandemic remains a threat to public health, researchers continue to detect new variants of the causative virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
The SARS-CoV-2 Omicron variant continues to spread rapidly and evades immunity, even in those vaccinated against the virus.
Study
The scientists used the widely detected Omicron BA5.2 strain as a control and compared it with both XBB.1 and XBB.3 variants by live virus neutralization test. The two XBB variants differ by a single mutation in the spike gene protein, where valine is substituted for glycine at position 252 (Gly252Val).
Serum samples from 30 recipients of the Pfizer mRNA or CoronaVac vaccines who had received two to four vaccine doses were used for the analysis. Of these 30 individuals, 25% had received two vaccine doses and were previously infected with BA.2.
Another 25% of the study cohort had received three doses and were previously infected with BA.2. About 30% of the study participants were infection-naïve and had received three vaccine doses, while the remaining participants had no infection history and had received four doses.
Antibody titers, which were measured as the geometric mean titer (GMT) of half-maximal neutralizing titer (NT50) (NT50GMT), were lower for both XBB strains. More specifically, NT50GMT values were 19 and 26 for XBB.1 and XBB.3, respectively, whereas the ancestral strain was associated with an exponentially higher titer of 436. Thus, the ancestral strain was associated with about 17- and 23-fold higher neutralizing titers than the XBB strains.
Neutralizing titers were comparably higher at three- and 4.5-fold against the ancestral strain than the BA.5.2 Omicron strain. There was a uniform reduction in the GMT against XBB strains in all vaccine recipient groups and those with a history of prior infection compared to titers against the ancestral strains.
In one patient with a prior BA.5.2 infection, the GMT was higher against the ancestral and BA.5.2 strains by 16-fold in convalescent serum compared to acute-phase serum. Interestingly, there was no rise in anti-XBB neutralizing titer in either type of serum sample.
Another patient with prior XBB.1 infection exhibited an increase in neutralizing titers against the ancestral strain by eight-fold; however, their titers were 20- and 30-fold greater against BA.5.2 and both XBB strains, respectively. Finally, the same trends, albeit much weaker, were observed in a third patient with a previous XBB.3 infection.
Conclusion
The results of the current study demonstrate that both XBB strains can evade protective immune antibodies much more efficiently than the ancestral or BA.5.2 strains, irrespective of whether the antibodies were elicited by prior infection or vaccination with either the Pfizer or CoronaVac vaccines.
The BA.5.2 lineage does not appear to induce neutralizing antibodies against XBB subvariants. Thus, the risk of reinfection or breakthrough infection is much higher in patients with a history of infection with BA.5.2 or who have received a bivalent vaccine that consists of both the ancestral and Omicron early spike proteins as compared with those infected with the ancestral variant.
Source:
https://www.news-medical.net/news/20221212/XBB-Omicron-variant-evades-vaccine-induced-immunity.aspx