--- title: Pfizer Vaccine Has 23% Efficacy Vs. Omicron Variant: Study description: A two-shot course of Pfizer’s vaccine has just 22.5% efficacy against symptomatic infection with the omicron variant, but can thwart severe disease, according to laboratory experiments. canonical: https://time.com/6127710/omicron-pfizer/ author: TIME article:opinion: false article:content_tier: free article:published_time: 2021-12-11T17:58:51.000Z article:modified_time: 2023-12-12T00:11:29.000Z article:section: Health og:title: Pfizer Vaccine Has 23% Efficacy Vs. Omicron in South African Lab Study og:description: The research considered blood plasma samples from 12 participants. og:url: https://time.com/6127710/omicron-pfizer/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt05f41a3931c38803/698a208e16d8842385c3a22e/Pfizer.jpg?branch=production&width=2400&quality=75&auto=webp&crop=16:9 og:image:width: 1200 og:image:height: 675 og:image:alt: SAFRICA-HEALTH-VIRUS-VACCINATION og:type: article twitter:card: summary_large_image twitter:title: Pfizer Vaccine Has 23% Efficacy Vs. Omicron in South African Lab Study twitter:description: The research considered blood plasma samples from 12 participants. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt05f41a3931c38803/698a208e16d8842385c3a22e/Pfizer.jpg?branch=production&width=2400&quality=75&auto=webp&crop=16:9 ---  # Pfizer Vaccine Has 23% Efficacy Vs. Omicron in South African Lab Study by [Antony Sguazzin/Bloomberg](https://time.com/author/bloomberg/) ## Antony Sguazzin/Bloomberg Contributor Updated: Dec 12, 2023 12:11 AM UTCPublished: Dec 11, 2021 5:58 PM UTC  A member of the Western Cape Metro EMS(Emergency Medical Services) prepares Pfizer vaccines from an ambulance which has been converted to facilitate vaccinations at a COVID 19 vaccination event in Manenberg, which is part of the Vaxi-Taxi mobile vaccination drive in Cape Town, SA, on n December 08, 2021. A member of the Western Cape Metro EMS(Emergency Medical Services) prepares Pfizer vaccines from an ambulance which has been converted to facilitate vaccinations at a COVID 19 vaccination event in Manenberg, which is part of the Vaxi-Taxi mobile vaccination drive in Cape Town, SA, on n December 08, 2021.RODGER BOSCH—AFP/Getty Images by [Antony Sguazzin/Bloomberg](https://time.com/author/bloomberg/) ## Antony Sguazzin/Bloomberg Contributor Updated: Dec 12, 2023 12:11 AM UTCPublished: Dec 11, 2021 5:58 PM UTC A two-shot course of Pfizer Inc.’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 modeling. The research considered blood plasma samples from 12 participants. Scientists found omicron resulted in about a 41-fold reduction in levels of neutralizing 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](https://secureservercdn.net/50.62.198.70/1mx.c5c.myftpupload.com/wp-content/uploads/2021/12/MEDRXIV-2021-267417v2-Sigal.pdf) released on Friday. There most likely continues to be sufficient protection against severe disease, they said. The team this week was the [first](https://www.bloomberg.com/news/articles/2021-12-07/omicron-doesn-t-escape-pfizer-vaccine-completely-lab-head-says) to show that the variant, found by scientists in South Africa and Botswana and announced on Nov. 25, could largely, but not totally, escape the antibodies produced by Pfizer’s vaccine. Still, they said a booster shot could increase immunity. That’s been backed up by studies carried out by Pfizer itself. Preliminary U.K. data released on Friday showed that boosters from AstraZeneca Plc and Pfizer/BioNTech SE improve protection against the omicron variant to as much as 75% in the early days after the shot. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/6127710/omicron-pfizer/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/6127710/omicron-pfizer/"},"headline":"Pfizer Vaccine Has 23% Efficacy Vs. 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