Vaccine effectiveness similar across all vaccines studied
AstraZeneca’s Vaxzevria (ChAdOx1-S [Recombinant]) was effective at preventing COVID-19 infections due to Omicron when used as a fourth dose booster, according to new data from Thailand’s Chiang Mai University.1
In the real-world evidence study, Vaxzevria showed vaccine effectiveness (VE) of 73% (95% Confidence Interval [CI] 48-89%) against the highly transmissible Omicron variant when a fourth dose was given on top of any previous primary or booster vaccine.1 According to the study authors, these are the first known data assessing the effectiveness of a mixed (heterologous) four-dose COVID-19 vaccine schedule.1
The findings were published as a preprint in Research Square .
The data showed that a fourth dose of any of the COVID-19 vaccines studied, including Vaxzevria, were 75% effective in preventing Omicron infection (VE 75%, 95% CI 71-80%). The VE of 73% for Vaxzevria was similar to that seen with mRNA vaccines which showed VE of 71% (VE 71%, 95% CI 59-79%). VE was adjusted for age, gender, calendar time and preceding vaccine series type.1
Lead author Emeritus Professor Suwat Chariyalertsak, MD, Dr.PH, Faculty of Public Health, Chiang Mai University, Thailand, said: “This study provides much-needed data showing a fourth dose of any COVID-19 vaccine can help prevent infection due to the highly contagious Omicron variant. Providing continuous protection with boosting is especially important for at-risk groups such as the elderly and those living with chronic health conditions. The data also support the effectiveness of heterologous, or ‘mix and match’, vaccination schedules which may help ongoing efforts to increase population coverage of booster doses.”
John Perez, Senior Vice President, Head of Late Development, Vaccines & Immune Therapies, AstraZeneca, added: “These new data further add to our understanding of the importance of booster doses to protect against COVID-19 infection in an evolving variant landscape. Building on Vaxzevria’s effectiveness in preventing severe disease and death, we now know that Vaxzevria can help prevent Omicron-related infections when given as a fourth dose, with greater protection against infection than was seen following a third dose.”
Additionally, a preliminary analysis of hospital data reports VE against severe COVID-19 (requiring invasive mechanical ventilation), and death during the Omicron wave in February and March of 2022. Across all age groups studied, a three-dose mixed schedule provided 98% protection against severe infection or COVID-19-related death. Following a fourth dose booster, the authors observed only a single death, in a person with comorbidities, suggesting very high effectiveness. Analysis of this dataset is ongoing and will be reported at a later date.1
The study reported real-world VE of Vaxzevria, CoronaVac and mRNA vaccines utilising an active surveillance network which enabled comparisons of the same patient profiles across both Delta-predominant and Omicron-predominant periods.1
To date, over 3 billion doses of Vaxzevria have been released, which based on model outcomes is estimated to have helped save over 6 million lives between 08 December 2020 and 08 December 2021.2
Notes
About the study1
The study is a test-negative, case-controlled analysis of data for the province of Chiang Mai, Northern Thailand, from the Ministry of Public Health Immunization Centre (MOPH IC) database, designed to estimate VE against SARS-CoV-2 infection (COVID-19) of various heterologous (mixed) vaccination schedules.
The study analysed data for the Delta-predominant period in Thailand (1 October to 31 December 2021), and the Omicron-predominant period (1 Feb to 10 Apr 2022), and aimed to evaluate the effectiveness of heterologous three dose COVID-19 vaccine schedules during the Delta period, and heterologous three and four dose schedules during the Omicron period.
Analysis for the Delta period included 27,301 participants (2,130 test-positive and 25,171 test-negative), and for the Omicron period there were 36,170 participants (14,682 test-positive and 21, 488 test-negative.)
A preliminary evaluation of a separate hospital patient management system provides a descriptive analysis of the impact of third and fourth dose boosters against severe COVID-19 and mortality.
Vaxzevria (ChAdOx1-S [Recombinant], formerly AZD1222)
AstraZeneca COVID-19 vaccine was invented by the University of Oxford. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.
Vaxzevria is a ‘viral vector’ vaccine, which means a version of a virus that cannot cause disease is used as part of the vaccine, leaving the body knowing how to fight it if it is exposed to the real virus later. 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.3
Vaxzevria has an acceptable safety profile, according to clinical studies and real-world evidence from tens of millions of people globally.4-10 Based on the millions of people vaccinated with Vaxzevria, very common adverse reactions reported included: headache, nausea, myalgia, arthralgia, injection site tenderness/pain/warmth/pruritus, fatigue, malaise, pyrexia, chills.11 The majority of adverse reactions were mild to moderate in severity and usually resolved within a few days of vaccination.11
The vaccine has been granted a conditional marketing authorisation or emergency use in more than 125 countries. It also has Emergency Use Listing from the World Health Organization, which accelerates the pathway to access in up to 144 countries through the COVAX Facility.
Under a sub-license agreement with AstraZeneca, the vaccine is manufactured and supplied by the Serum Institute of India under the name COVISHIELD.
AstraZeneca
AstraZeneca (LSE/STO/Nasdaq: AZN) is a global, science-led biopharmaceutical company that focuses on the discovery, development, and commercialisation of prescription medicines in Oncology, Rare Diseases, and BioPharmaceuticals, including Cardiovascular, Renal & Metabolism, and Respiratory & Immunology. Based in Cambridge, UK, AstraZeneca operates in over 100 countries and its innovative medicines are used by millions of patients worldwide. Please visit astrazeneca.com and follow the Company on Twitter @AstraZeneca.
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References
1. Chariyalertsak S, et al. Effectiveness of heterologous 3rd and 4th dose COVID-19 vaccine schedules for SARS-CoV-2 infection during delta and omicron predominance in Thailand. Available at: Effectiveness of heterologous 3rd and 4th dose COVID-19 vaccine schedules for SARS-CoV-2 infection during delta and omicron predominance in Thailand. | Research Square. Accessed June 2022
2. Data estimates based on model outcomes from separate analyses conducted by Airfinity and Imperial College, United Kingdom. AstraZeneca Data on File. REF-156573, 11 July 2022
3. Centers For Disease Control and Prevention. Understanding Viral Vector COVID-19 Vaccines. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/viralvector.html?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fvaccines%2Fcovid-19%2Fhcp%2Fviral-vector-vaccine-basics.html Last accessed July 2022.
4. Burn, E et al, Thrombosis and thrombocytopenia after vaccination against and infection with SARS-CoV-2: a population-based cohort analysis. Available at: https://www.medrxiv.org/content/10.1101/2021.07.29.21261348v1.full. Accessed March 2022 Last accessed July 2022.
5. Burn, E et al, Thromboembolic Events and Thrombosis With Thrombocytopenia After COVID-19 Infection and Vaccination in Catalonia, Spain. Available at SSRN: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3886421 Last accessed July 2022.
6. P. Bhuyan et al. Very rare thrombosis with thrombocytopenia after second AZD1222 dose: a global safety database analysis. Lancet. Available at: https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(21)01693-7.pdf Last accessed July 2022.
7. Laporte JR et al. Vaccines against Covid-19, venous thromboembolism, and thrombocytopenia. A population-based retrospective cohort study. Available at https://www.medrxiv.org/content/10.1101/2021.07.23.21261036v1 Last accessed July 2022.
8. Voysey M, et al. Single-dose administration and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine: a pooled analysis of four randomised trials. The Lancet 2021; 397: 881-91. Last accessed July 2022.
9. Falsey A, et al. Phase 3 safety and efficacy of AZD1222 (ChAdOx1nCoV-19 Vaccine. NEJM. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa2105290?query=featured_coronavirus Last accessed July 2022.
10. Flaxman A, et al. Reactogenicity and immunogenicity after a late second dose or a third dose of ChAdOx1 nCoV-19 (AZ2021D1222) in the UK: a substudy of two randomized controlled trials (COV001 and COV002). The Lancet 2021; 398: 981-90. Last accessed July 2022.
11. WHO Summary of Product Characteristics. COVID-19 Vaccine AstraZeneca. December, 2021; https://www.covax.azcovid-19.com/content/dam/azcovid/pdf/covax/who-clean-smpc-azd1222-en.pdf Last accessed July 2022