Pfizer and AstraZeneca’s COVID-19 vaccines are not as effective in fighting off the Omicron variant compared to other strains, according to a new study published Monday.

Researchers from the University of Oxford said in the pre-print paper that they had discovered a “substantial fall” in neutralizing antibodies when the Omicron variant was introduced to blood samples 28 days after participants received their second dose of either Pfizer or AstraZeneca’s vaccine.

The study, which has yet to be peer-reviewed, discovered that some of the participants “failed to neutralize [the virus] at all.”

Pfizer jabs protect 70% against hospitalization from omicron

A two-dose Pfizer/BioNTech vaccination provides just 33% protection against infection by the omicron variant of the coronavirus, but 70% protection against hospitalization, according to a large-scale analysis in South Africa released Tuesday.

The first large-scale analysis of vaccine effectiveness in the region where the new variant was discovered appears to support early indications that omicron is more easily transmissible and that the Pfizer shot isn’t as effective in protecting against infection as it was against the delta variant.

The analysis was based on more than 211,000 positive COVID-19 test results, 41% from adults who had received two doses of the Pfizer vaccine. About 78,000 of these positive COVID-19 test results between Nov. 15 and Dec. 7 were attributed to omicron infections. The study was carried out by Discovery Health, South Africa’s largest private health insurer, and the South African Medical Research Council.