AstraZeneca among COVID-19 booster vaccines still effective vs. Omicron — study

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In the photo (L-R): Dr. Rontgene Solante, Vice President of the Philippine College of Physicians; Dr. Diana Payawal, President of the Philippine College of Physicians; and Dr. Anna Ong-Lim, Chief of the Infection and Tropical Disease Division of the UP Philippine General Hospital (UP PGH). Photo from the Philippine College of Physicians

Metro Manila (CNN Philippines) — If you haven't gotten your third dose, you might want to schedule your shots soon as a study confirms that all current vaccines, including AstraZeneca, are likewise effective against severe effects of the Omicron variant of COVID-19.

The review is based on the assessment of 22 independent infectious diseases experts using ViewHub, a database on vaccine use developed and maintained by the International Vaccine Access Center (IVAC) and the Johns Hopkins Bloomberg School of Public Health. It covers more than 50 real-world studies of vaccine effectiveness against COVID-19.

The effectiveness of COVID-19 vaccines in an Omicron world

Dr. Rontgene Solante, one of the review authors, stressed the high protection given by existing vaccines, including AstraZeneca, when used as a booster.

"Current vaccines are still effective in protecting the vulnerable populations. Instead of focusing our resources on getting variant-specific booster vaccines, it is important that all governments and all countries will focus on how to increase vaccination coverage and how to increase uptake of booster vaccination in the population," Solante said during a forum organized by the Philippine College of Physicians.

The review shows that boosting with AstraZeneca's vaccine and mRNA COVID-19 vaccines provide equally high protection against Omicron-related severe outcomes, including hospitalization and death, even as new subvariants of the virus emerge.

It adds that any three-dose schedule, including the AstraZeneca vaccine, is highly effective at protecting against severe Omicron outcomes. A homologous three-dose of AstraZeneca recorded 84.8% vaccine effectiveness. Mixed three-dose schedules also showed equivalent effectiveness of 86.7% (AstraZeneca as primary vaccine + Pfizer as a booster) and 89.2% (AstraZeneca as primary vaccine + Moderna as a booster) (1).

Dr. Anna Ong-Lim, Chief of the Infection and Tropical Disease Division of the UP Philippine General Hospital (UP PGH). Photo from the Philippine College of Physicians

The reviewed data also showed that other vaccines used as boosters perform well against Omicron, but appeared slightly less effective than AstraZeneca's vaccine and the mRNA COVID19 vaccines.

This can be attributed to AstraZeneca being a viral vector vaccine, which means a version of a virus that cannot cause disease is used as part of the vaccine. If the body is exposed to the real virus later, it can fight it. This vaccine technology has been used by scientists over the past 40 years to fight other infectious diseases such as the flu, Zika, Ebola, and HIV.

4th dose effectiveness vs. Omicron-related severe effects

Dr. Christopher Lee, Hospital Sungai Buloh (Malaysia). Photo from the Philippine College of Physicians

A real-world study from Thailand shows a fourth dose booster is likely to add a significant level of additional protection.

Presented by Dr. Suwat Chariyalertsak of Chiang Mai University, the study shows that people who were vaccinated with a fourth dose of either the AstraZeneca vaccine or an mRNA COVID-19 vaccine from February to April 2022 did not experience severe effects of Omicron (2). The research, however, is yet to be peer-reviewed.

"Vaccine coverage, rather than vaccine type — either mixed or homologous — may be a much stronger predictor of protection against severe outcomes (of Omicron)," Chariyalertsak said.

The infectious diseases experts emphasized the importance of vaccine coverage in the ongoing effort to save lives amid emerging variants of COVID-19.

Photo from the Philippine College of Physicians

For its part, AstraZeneca and its global partners have released over three billion vaccine doses to more than 180 countries, and approximately two-thirds of these doses have been delivered to low and lower-middle-income countries. The vaccine is estimated to have helped save over six million lives during the first 12 months of use since December 2020, according to data from leading health analytics firm Airfinity.

*This non-promotional, informational material is provided as service to patients. There is no intent to replace the advice of a healthcare professional. Always consult your doctor*


1. Solante R, Alvarez-Moreno C, Burhan E et al. Expert Review of Global Real-World Data on COVID-19 Vaccine Booster Effectiveness & Safety during the Omicron-dominant phase of the pandemic. 6 September 2022, REPRINT (Version 1) available at Research Square. Accessed September 2022.

2. Intawong K, et al. Heterologous third and fourth dose vaccine to reduce severity and mortality in COVID-19 patients during delta and omicron predominance: A cohort study in Chiang Mai, Thailand. Research Square 2022. Preprint published online, not peer reviewed, Accessed August 2022.