A two-shot course of Pfizer’s vaccine may have just 22.5% efficacy against symptomatic infection with the Omicron variant, but can thwart severe disease, according to laboratory experiments in South Africa.
Researchers at the Africa Health Research Institute in Durban issued additional data on a small study released earlier this week from which they made an estimate of the efficacy of the vaccine using modelling.
Bloomberg reports that the research considered blood plasma samples from 12 participants. Scientists found Omicron resulted in about a 41-fold reduction in levels of neutralising antibodies produced by people who had received two doses of the Pfizer-BioNTech SE shot, compared with the strain detected in China almost two years ago.
This is “essentially compromising the ability of the vaccine to protect against infection”, said the team of scientists led by laboratory head Alex Sigal in a preprint released last Friday (9 December). There probably would continue to be sufficient protection against severe disease, they added.
This week the team was the first to show that the variant, found by scientists in South Africa and Botswana and announced on 25 November, could largely, but not totally, escape the antibodies produced by Pfizerʼs vaccine. Still, they said a booster shot could increase immunity. Thatʼs been backed up by studies carried out by Pfizer itself.
Pre-print study details
SARS-CoV-2 Omicron has extensive but incomplete escape of Pfizer BNT162b2 elicited neutralisation and requires ACE2 for infection
Sandile Cele, Laurelle Jackson, Khadija Khan, David Khoury, Thandeka Moyo-Gwete, Houriiyah Tegally, Cathrine Scheepers, Daniel Amoako, Farina Karim, Mallory Bernstein, Gila Lustig, Derseree Archary, Muneerah Smith, Yashica Ganga, Zesuliwe Jule, Kajal Reedoy, James Emmanuel San, Shi-Hsia Hwa, Jennifer Giandhari, Jonathan Blackburn, Bernadett Gosnell, Salim Abdool Karim, Willem Hanekom, NGS-SA, COMMIT-KZN Team, Anne von Gottberg, Jinal Bhiman, Richard Lessells, Mahomed-Yunus Moosa, ProfileMiles Davenport, Tulio de Oliveira, Penny Moore, Alex Sigal.
Abstract
The emergence of the Omicron variant (1) of SARS-CoV-2 in November 2021 in South Africa has raised concerns that, based on the large number of mutations in the spike protein and elsewhere on the virus (https://covdb.stanford.edu/page/mutation-viewer/#sec_b-1-351), this variant will have considerable escape from vaccine elicited immunity. Furthermore, several mutations in the receptor binding domain and S2 are predicted to impact transmissibility and affinity for ACE-2.
Here we investigated whether Omicron escapes antibody neutralization elicited by the Pfizer BNT162b2 mRNA vaccine and whether the virus still requires binding to the ACE2 receptor to infect cells. We used an early passage of isolated and sequence confirmed live Omicron virus isolated in South Africa. We used a human lung cell line clone (H1299-ACE2) engineered to express the ACE2 receptor to both isolate the virus and test neutralization. We also tested growth in the parental H1299 which do not overexpress ACE2 and are not appreciably infectable with SARS-CoV-2. The H1299-ACE2 cells were similar to Vero-E6 in titer dependent focus formation, but were considerably more sensitive.
We observed that Omicron infected the ACE2-expressing cells in a concentration dependent manner but did not infect the parental H1299 cells, indicating that ACE2 is required for Omicron entry. We then tested the ability of plasma from BNT162b2 vaccinated study participants to neutralize Omicron versus ancestral D614G virus in a live virus neutralization assay. We tested 14 plasma samples from 12 participants, with 6 having no previous record of SARS-CoV-2 infection nor detectable nucleocapsid antibodies indicative of previous infection. For two of these participants, we used samples from two timepoints. The remaining 6 participants had a record of previous infection in the first SARS-CoV-2 infection wave in South Africa where infection was with ancestral D614G virus. Geometric mean titer (GMT) FRNT50 (inverse of the plasma dilution required for 50% reduction in infection foci number) was 1321 for D614G. These samples therefore had very strong neutralization of D614G virus, consistent with sampling soon after vaccination. GMT FRNT50 for the same samples was 32 for Omicron, a 41-fold decline. However, the escape was incomplete, with 5 of the participants, all previously infected, showing relatively high neutralization titers with Omicron.
Beta variant escape from BNT162b2 in a live virus neutralization assay has been reported to be substantial and our own data confirmed these results, with about 3-fold reduction in FRNT50. The results we present here with Omicron show much more extensive escape. However, escape was incomplete in participants with higher FRNT50 due to previous infection. Previous infection, followed by vaccination or booster is likely to increase the neutralisation level and likely confer protection from severe disease in Omicron infection.
Bloomberg article – Pfizer Course May Have 23% Efficacy Vs. Omicron: Study (Restricted access)
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Triple shot of Pfizer vaccination ‘neutralises Omicron variant
Omicron: Some simple steps to deal with the new variant
Mixing COVID-19 vaccinations gives better immune response — Oxford trial