What Is The Difference Between Astrazeneca And Pfizer

The emergence of COVID-19 has necessitated the rapid development and distribution of vaccines worldwide, with AstraZeneca and Pfizer leading the charge. Each vaccine has its unique origin, components, and technology, contributing differently to the global fight against the pandemic. This divergence raises important considerations regarding efficacy, side effects, and accessibility.

The primary difference between the AstraZeneca and Pfizer vaccines lies in their technological foundations and resultant efficacy. AstraZeneca uses a viral vector approach, while Pfizer employs mRNA technology. This leads to varying degrees of effectiveness against different strains of the virus and differences in storage requirements, impacting their global distribution and usage strategies.

As countries roll out these vaccines, the decision of which vaccine to administer depends on various factors including logistical capabilities, population needs, and existing healthcare infrastructure. The nuanced distinctions between the two vaccines play a crucial role in shaping public health strategies and individual choices across diverse global contexts.

Vaccine Overview

AstraZeneca Basics

Origin and Development

The AstraZeneca COVID-19 vaccine, known as AZD1222, was developed through a collaboration between AstraZeneca, a global biopharmaceutical company, and Oxford University. The development phase began in January 2020, with the aim of finding a viable vaccine to counter the rapidly spreading SARS-CoV-2 virus. By November 2020, AstraZeneca announced that its vaccine had shown high efficacy in interim analysis from clinical trials, paving the way for emergency use approval across various countries.

Key Components

The AstraZeneca vaccine is characterized by its use of a viral vector technology. It employs a harmless virus, a chimpanzee adenovirus, modified to carry the genetic material that codes for the spike protein of the novel coronavirus. Once administered, this vector induces cells in the body to produce the viral protein, which in turn stimulates the immune system to recognize and fight the coronavirus without exposing the recipient to the disease itself.

Pfizer Basics

Origin and Development

The Pfizer-BioNTech COVID-19 vaccine, branded as Comirnaty, represents a landmark in medical technology as it is one of the first widely used vaccines developed using mRNA technology. The development started in early 2020 in partnership between Pfizer, a U.S. pharmaceutical giant, and BioNTech, a German biotechnology company. The vaccine was found to have an efficacy rate of over 90% in preventing COVID-19 infections in its phase 3 clinical trial, leading to emergency authorization in various countries by December 2020.

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Key Components

Pfizer’s vaccine utilizes messenger RNA (mRNA) to combat COVID-19. This mRNA carries genetic instructions that help cells in the human body create the SARS-CoV-2 spike protein autonomously. This presence of the spike protein triggers an immune response without causing the disease, training the immune system to recognize and combat the actual virus if it enters the body.

Efficacy Comparison

AstraZeneca Performance

Clinical Trial Results

In its extensive phase 3 clinical trials, the AstraZeneca vaccine demonstrated an average efficacy of 70% in preventing COVID-19 infection. This efficacy varied slightly depending on the dosage regimen used, with a half dose followed by a full dose reaching up to 90% efficacy.

Effectiveness Against Variants

The AstraZeneca vaccine has shown mixed effectiveness against various coronavirus variants. It retains significant efficacy against the Alpha variant but has reduced efficacy against the Beta and Delta variants. Ongoing studies and modifications are being evaluated to enhance its efficacy against new strains.

Pfizer Performance

Clinical Trial Results

The phase 3 clinical trials for the Pfizer vaccine showed an efficacy of approximately 95% in preventing COVID-19 infections. This high efficacy rate was consistent across different age groups, genders, and ethnicities, demonstrating robust protection against the disease.

Effectiveness Against Variants

Pfizer’s vaccine is also effective against several variants of the coronavirus, including Alpha and Delta. Studies suggest that while efficacy against some variants like Beta may be slightly reduced, the vaccine still provides substantial protection against severe disease and hospitalization.

Side Effects

AstraZeneca Reactions

Common Side Effects

Individuals receiving the AstraZeneca vaccine have reported common side effects such as:

  • Pain at the injection site
  • Fatigue
  • Headache
  • Fever and chills

These side effects generally resolve within a few days of receiving the vaccine.

Serious Side Effects

While rare, some serious side effects have been noted, including cases of blood clots combined with low levels of blood platelets, primarily among younger women. These instances are extremely rare but have influenced public health recommendations in some countries regarding vaccine use.

Pfizer Reactions

Common Side Effects

Common side effects for the Pfizer vaccine include:

  • Injection site reactions
  • Fatigue
  • Headache
  • Fever
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These reactions are typically mild to moderate and resolve within a few days.

Serious Side Effects

Serious reactions to the Pfizer vaccine are rare but can include severe allergic reactions like anaphylaxis. Monitoring and emergency treatments are standard protocols during vaccination sessions to manage any severe reactions immediately.

Global Use

AstraZeneca Accessibility

Distribution in Low-Income Countries

AstraZeneca’s vaccine has been pivotal in global efforts to combat COVID-19, especially in low-income countries. Due to its less stringent storage requirements (standard refrigeration at 2-8 degrees Celsius) compared to mRNA vaccines, it has been easier to distribute in regions with less developed healthcare infrastructure. Organizations like COVAX, which aim to provide equitable access to COVID-19 vaccines, have heavily relied on AstraZeneca due to these logistics.

Cost Considerations

One of the most compelling advantages of the AstraZeneca vaccine is its cost-effectiveness. Produced on a not-for-profit basis during the pandemic, it is priced at approximately $2-3 per dose, which is significantly lower than mRNA vaccines. This affordability has enabled widespread distribution and administration in developing countries, helping to mitigate the global spread of the virus.

Pfizer Accessibility

Distribution in Low-Income Countries

The distribution of Pfizer’s vaccine in low-income countries has faced challenges, primarily due to its ultra-low temperature storage requirements (-70 degrees Celsius). This requirement necessitates specialized equipment and logistics, which are often not available in less developed regions. However, Pfizer has pledged doses to COVAX and is working on formulations that might be easier to store and distribute.

Cost Considerations

Pfizer’s vaccine is more expensive than AstraZeneca’s, with prices ranging from $15 to $20 per dose. This higher cost has made it less accessible in many low-income countries without substantial financial aid or donations from wealthier nations or international organizations.

Immunization Schemes

AstraZeneca Schedule

Recommended Dosage and Intervals

The AstraZeneca vaccine is typically administered in two doses. The recommended interval between the first and second dose has varied, with suggestions ranging from 4 to 12 weeks. Extending the interval to 12 weeks has been shown to potentially enhance the efficacy of the vaccine.

Pfizer Schedule

Recommended Dosage and Intervals

The Pfizer vaccine also requires two doses for full effectiveness. The recommended interval between doses is 21 days. Adhering to this schedule is crucial for achieving the high efficacy rates reported in clinical trials.

Public Perception

AstraZeneca Views

Public Trust and Hesitancy

Public trust in the AstraZeneca vaccine has experienced fluctuations, particularly in Europe, where reports of rare blood clots led some countries to temporarily pause its use. However, regulatory agencies like the WHO and the EMA have affirmed its safety, emphasizing that its benefits far outweigh the risks.

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Pfizer Views

Public Trust and Hesitancy

The Pfizer vaccine has generally enjoyed high levels of public trust, particularly in Western countries, due to its high efficacy rates and robust safety data. However, hesitancy still exists, driven by concerns over the new mRNA technology and rapid development timeline.

Future Outlook

AstraZeneca Developments

Upcoming Trials and Updates

AstraZeneca continues to conduct trials to extend its vaccine’s approval for use in children and to study its effectiveness as a booster against emerging variants. The company is also exploring a modified version of the vaccine to specifically target variants of concern.

Pfizer Developments

Upcoming Trials and Updates

Pfizer is also actively researching the use of its vaccine in younger age groups, booster doses, and its efficacy against new variants. Recent developments include the approval of booster shots in many countries, intended to enhance immunity as the virus evolves.

Frequently Asked Questions

What is the AstraZeneca vaccine?

The AstraZeneca vaccine, developed in collaboration with Oxford University, utilizes a modified version of a common cold virus (adenovirus) from chimpanzees. It introduces the spike protein of the SARS-CoV-2 virus to the immune system, preparing it to recognize and combat the virus without causing the disease.

How does the Pfizer vaccine work?

The Pfizer vaccine, developed by Pfizer and BioNTech, uses messenger RNA (mRNA) to instruct cells to produce a protein that triggers an immune response. This response prepares the immune system to attack the SARS-CoV-2 virus if the body is exposed to it in the future.

What are the storage requirements for these vaccines?

Pfizer’s vaccine requires storage at ultra-low temperatures, around -70 degrees Celsius, making its distribution more challenging, especially in regions with limited infrastructure. In contrast, the AstraZeneca vaccine can be stored at standard refrigeration temperatures, facilitating easier and broader distribution.

Are there any severe side effects associated with these vaccines?

Both vaccines have shown high safety profiles with typical side effects similar to other vaccines, including pain at the injection site, fatigue, and fever. Serious side effects are rare but have been documented and are continuously monitored by health authorities worldwide.


The choice between AstraZeneca and Pfizer vaccines extends beyond basic efficacy and side effects to consider global accessibility and logistic viability. As the world continues to combat COVID-19, the role of vaccines in ending the pandemic is undeniable, yet each vaccine’s characteristics must be aligned with specific regional needs and capabilities.

Understanding the differences between these vaccines is more than an academic exercise; it is a critical component of global health strategy and personal health decisions. As new variants of the virus emerge and new data becomes available, ongoing research and adaptation will be crucial in the collective journey towards a post-pandemic world.

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