One study published Monday by Stockholm’s Karolinska Institute finds that omicron does, indeed, appear to reduce the effectiveness of vaccines in some people, but also that the decrease in efficacy varies widely, with some people maintaining immunity at levels consistent with prior versions of the virus. On the one hand, some blood sera show a greatly resistant antibody response. “We find neutralizing antibody responses in pooled reference sera sampled shortly after infection or vaccination are substantially less potent against Omicron, with neutralizing antibody titers reduced by up to 45 fold compared to those for the pandemic founder,” write authors Daniel J. Sheward, Changil Kim, Roy A. Ehling, Alec Pankow, Xaquin Castro Dopico, Darren Martin, Sai Reddy, Joakim Dillner, Gunilla B. Karlsson Hedestam, Jan Albert, and Ben Murrell, in the paper “Variable loss of antibody potency against SARS-CoV-2 B.1.1.529 (Omicron),” posted Monday on the BioarXiv pre-print server. Despite that reduction in potency, the authors write, others showed an ability to generate neutralizing antibodies at nearly unreduced levels, with the difference being those individuals had had COVID-19 at some point and also had been vaccinated. “Sera from infected-then-vaccinated healthcare workers exhibited robust cross-neutralization of Omicron, with an average potency reduction of only 5-fold relative to the pandemic founder variant, and some donors showing no loss at all. The authors conclude the highly varied response shows “the extensive but incomplete evasion of neutralizing antibody responses by the Omicron variant.” They also conclude that it “suggests that increasing the magnitude of neutralizing antibody responses by boosting with unmodified vaccines may suffice to raise titers to levels that are protective,” meaning boosting the antibody generation in individuals. The paper is not yet peer-reviewed, and so its results should be viewed with caution. Since it appeared, Omicron has caused alarm because of how fast it spreads. The U.S. Centers for Disease Control on Monday announced that Omicron now makes up 73% of U.S. cases of SARS-CoV-2, up from 13%. That pace has outstripped the CDC’s expectations, according to The Financial Times’s Peter Wells and Kiran Stacey. The element of Omicron that has struck researchers is how much it has mutated versus the previous four strains of the virus. In particular, the spike protein, where the “receptor binding domain” dwells, has undergone more than thirty transformations from its form in prior variants. The RBD is the main target for antibodies that can block the virus’s activity, and so scientists are trying to determine to what extent the mutations are allowing the virus to escape antibodies’ neutralizing effects. The study is very small, which could render its finding less certain. The researchers studied blood sera from 17 “randomly selected seropositive recent blood donors” who were “anonymized and therefore unknown exposure and vaccination status,” as the first cohort. They also then studied 17 “recently-sampled hospital workers who were infected in May 2020, with varied subsequent vaccination histories.” The authors write that they noticed greater effectiveness in antibody activity in those health workers who had a double dose of the COVID vaccine made by Pfizer and BioNTech, “BNT162b2.” The authors conclude from the increased antibody effect in the vaccinated health workers that it is the repeated exposure to the virus that may “broaden” immune response, perhaps to the point where it can handle mutations of the spike protein and RBD. “This suggests that responses to SARS-CoV-2 spike broaden with increasing antigenic exposure,” they write. “This has been characterized against other variants in the context of both prior infections16 and three-dose vaccinations.”
