Pfizer-BioNTech’s bivalent COVID-19 vaccine may not protect cancer patients from the most common omicron subvariant in circulation now, according to research published in Cancer Cell.1

Researchers found that the bivalent vaccine increased virus-neutralizing capacity against the BQ.1.1 subvariant but not against the XBB.1 and XBB.1.5 subvariants.

XBB.1.5 is the most common variant circulating in the United States right now, according to data from the US Centers for Disease Control and Prevention.2 XBB.1.5 makes up 74.7% of reported cases, BQ.1.1 makes up 15.3%, and XBB.1 makes up 1.9%.

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For this study, researchers assessed antibody responses to Pfizer-BioNTech’s bivalent COVID-19 vaccine in 101 patients with hematologic cancers and 13 patients with solid tumors.1 All patients had insufficient responses after their second vaccination with Pfizer-BioNTech’s monovalent vaccine.

The researchers measured SARS-CoV-2 spike-specific IgG (anti-S) antibody levels and virus neutralization in these patients after their fourth dose of the monovalent vaccine and before and after administration of the bivalent vaccine.

Anti-S antibody levels and neutralizing capacity toward BQ.1.1 increased significantly after the bivalent vaccine, compared with after the fourth dose of the monovalent vaccine and before administration of the bivalent vaccine (P <.001).

Neutralizing capability toward BQ.1.1 was attained in 55% (24/44) of patients who did not have a protective response before receiving the bivalent vaccine. 

In a cohort of 19 evaluable patients, the proportion of patients with antibody levels below the neutralizing threshold after bivalent vaccination was 42% for XBB.1, 32% for XBB.1.5, and 10.5% for BQ.1.1.

A comparison of the estimated mean neutralization titer showed that responses toward XBB.1 and XBB.1.5 were “strikingly” low — 1:13 and 1:14, respectively — compared with 1:344 for the original strain of SARS-CoV-2, 1:83 for the BA.5 subvariant, and 1:39 for the BQ.1.1 subvariant.

The researchers concluded that Pfizer-BioNTech’s bivalent mRNA vaccine “largely fails to protect” against the XBB.1 and XBB.1.5 omicron subvariants in immune-deficient patients with cancer but does provide some protection against the BQ.1.1 subvariant. 

The researchers emphasized the need for updated vaccines and effective antiviral drugs for this vulnerable group of patients.

1. Ehmsen S, Pedersen RM, Bang LL, et al. BQ.1.1, XBB.1, and XBB.1.5 neutralization after bivalent mRNA COVID-19 booster in patients with cancer. Cancer Cell. Published online February 9, 2023. doi:10.1016/j.ccell.2023.02.003

2. Summary of variant surveillance. COVID Data Tracker. US Centers for Disease Control and Prevention. Accessed February 14, 2023.

This article originally appeared on Cancer Therapy Advisor