The AstraZeneca Vaccine: Better than its reputation


published on 1 April 2021

Among scientists, the consensus is that only a vaccination against COVID-19 can efficiently end the pandemic in a reasonable timescale. A number of different vaccines are currently used in national vaccination campaigns. In particular, the ChAdOx1-vaccine by AstraZeneca was recently discussed to be less beneficial and less safe than expected. In this article, we summarise some of the recent scientific findings and explain why the AstraZeneca vaccine is both highly efficient and absolutely necessary in the fight against SARS-CoV-2.


The purpose of the vaccines against COVID-19 is to end the pandemic. In practical terms, they have multiple benefits: they can avoid a severe course of the disease and hospitalisation, reduce the transmission of the virus or provide protection against current variants. Here, we highlight the most important things you need to know about the AstraZeneca vaccine:

1. No severe side effects have been reported for the AstraZeneca vaccine

During its approval process by the European Medicines Agency (EMA), also the vaccination effects of the AstraZeneca vaccine have been examined thoroughly. Apart from the common effects of vaccines such as temporary pain at the injection site, headache and fatigue, no unusual side effects have been found. These effects are completely normal and show that immune system is active and responds to the vaccine. However, as other COVID-19 vaccines also the AstraZeneca vaccine shows a higher reactogenicity than classical vaccines. Recently, scattered cases of a specific type of thrombosis have been reported in several countries which were suspected to be linked to the vaccination. Such an occurrence of blood clots was reviewed in 25 cases out of 20 million vaccinated people, according to the EMA. Moreover, in a recent study by AstraZeneca no elevated risk for thrombosis cold be detected compared to the incidence in the unvaccinated general public. Both the EMA and the WHO come to the conclusion that up to now no causality has been shown and thus the benefits of the AstraZeneca vaccine outweigh its side effects. Therefore, they recommend its further use in the fight against the pandemic. Some countries have nevertheless adapted the age range in which people will receive the AstraZeneca vaccine. Luxembourg follows the advice of EMA (status 31 March 2021). 

2. The AstraZeneca vaccine can benefit also people over 65 years of age

Initially, several countries had decided to only apply the AstraZeneca vaccine for people below 65 years of age after it was approved by the European Medicines Agency (EMA) at the end of January 2021. The reason for this was not a lack of safety of efficacy of the vaccine, but rather a lack of data for this particular age group. The design of clinical trials to test vaccines defines the conditions under which it can be approved and administered later on. The clinical trials of the AstraZeneca vaccine primarily assessed people below 65 years, hence the vaccine was limited to use in that age group in several countries. A lack of data does however not imply any concern about safety (the same also holds true for pregnant and breastfeeding women). 

In fact, a recent study from Scotland on 5.4 million vaccinated people showed that the AstraZeneca ChAsOx1-vaccine prevents hospitalisations by 94% within four weeks after vaccination. Apart from the UK, other countries also started to recommend that vaccine can also be used for people over 65 years, among them Germany and France.

3. The AstraZeneca vaccine is very effective.

A factor often used to rate the quality of vaccines is their efficacy. For the AstraZeneca vaccine an efficacy of 76% against a symptomatic infection was reported after the first injection and this can be increased to 82% upon the second injection. Another study reports an efficacy of 84% against the initial and still 75% protection against the UK-variant of the virus, showing that the vaccine also offers substantial protection against this more transmissible variant. In contrast, the efficacy of the Pfizer/BioNTech and Moderna mRNA vaccines is reported in clinical studies to be 95% and 94%, respectively. However, all of the abovementioned efficacy reports reflect the proportion of people which show any type of COVID-19 symptoms, including also light courses. If one compares how well the vaccines protect against severe courses of COVID-19 (which challenge the health system and eventually may cause death), the protection by the AstraZeneca vaccine is reported to be 100%, similar to the mRNA vaccines.

In other words: After being vaccinated with ChADOx1, slightly more people might experience mild and temporary symptoms following a COVID-19 infection, but the protection against a severe and deadly course of the disease is as good as for any other COVID-19 vaccine currently on the market.

Finally, compared to vaccines against other diseases, all COVID-19 vaccines perform extremely well: For example the effectiveness of the influenza vaccination against the seasonal flu was reported to be 21% in 2018/2019 and only 15% in 2017/2018 in Germany. Generally, not more than 60% effectiveness is achieved by seasonal vaccinations against influenza.

4. Transmission of the virus is significantly reduced

The AstraZeneca vaccine was the first that was reported to reduce the transmission of COVID-19 by as much as 67%, slowing down the spread of the virus. In addition to reducing symptoms and avoiding a severe course of COVID-19, the vaccination can tremendously contribute to stop the spread of the disease. It is known that a large proportion of people infected with SARS-CoV-2 show only minor or no symptoms, yet they still can transmit the virus and infect others.

In reducing this transmission, getting vaccinated with the AstraZeneca vaccine will contribute herd immunity, as the SARS-CoV-2 virus is expected to become endemic.

5. The AstraZeneca vaccine is less effective against light disease courses of the South African SARS-CoV-2 variant

Another general concern is the effectiveness of the different vaccines against other strains, such as the B.1.351 SARS-CoV-2 variant from South Africa. This strain of the virus acquired a change in the composition of the spike protein, which is the major target for most of the current COVID-19 vaccines.

Specific studies with the South African mutants showed a reduced effectiveness of 22% in preventing light courses upon infection with this mutated variant. As a consequence,  the administration of the AstraZeneca vaccine was suspended in South Africa. However, the underlying study did not assess protection against severe courses of the disease as only young adults were included. In addition, only the antibody response was assessed, although this constitutes only a part of the immune response. In contrast, the impact of the B.1.351 SARS-CoV-2 variant on the T cell immune response is negligible. T cells generally provide an efficient long-term immune memory against SARS-CoV-2.

Experts thus expect that the AstraZeneca vaccine will still protect against severe courses, also against the South-African B.1.351 mutation. Therefore, the WHO still recommends the utilization of the AstraZeneca vaccine even if mutated forms of the virus are reported in the country. Notably, the effectiveness against the South-African variant of SARS-CoV-2 was also lower for the vaccines from Pfizer/BioNTech and Moderna.

Currently, the South African variant still only plays a minor role in the over infection events in Luxembourg and the rest of Europe, whereas the British variant B.117 is currently becoming predominant.

6. AstraZeneca vaccines requires much simpler logistics.

The AstraZeneca vaccine can tremendously facilitate the logistics of distribution: In contrast to the mRNA vaccines by Pfizer/BioNTech and Moderna, it can be stored in the fridge for up to half a year. In practical terms, this could mean that also treating physicians will be able to administer the vaccine and could be soon supporting the vaccination centres. This could significantly speed up the roll-out of the vaccine.

Recently, the phase 5a of the national vaccination campaign was started which includes all Luxembourg residents from the age of 55 upwards. This also includes using the AstraZeneca vaccines which has proven essential in the fight against the pandemic and meets the same safety criteria as any other vaccine on the market. For a country to vaccinate a significant proportion of its people in a short amount of time while still coping with shortages in overall vaccine supply, it is important that all good options are exploited efficiently. It is of utmost importance to protect against severe courses of disease and hence death as soon as possible. If hence many people turn down a very performant AstraZeneca vaccine just because it might be slightly less effective in preventing mild courses of disease or because of misinformation, this could significantly prolong the fight against the pandemic with all its consequences on public health and economy.


This article is based on current scientific findings published in internationally renowned journals. More information on the AstraZeneca vaccine can also be found on the websites of the WHO or the EMA.



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