The Romanian government, through CNCAV, has published the first information on how the AstraZeneca vaccine works, recently approved by the European Medicines Agency for use among the adult population.
"How does the newly licensed vaccine developed by AstraZeneca/Oxford work?
The vaccine developed by AstraZeneca/Oxford (ChAdOx1-S) is a non-replicating viral vector vaccine. There are other vaccines in development based on this technology against diseases caused by viruses such as HIV and Zika. An Ebola vaccine based on a non-replicating viral vector has already been authorized in the European Union.
These types of vaccines use another virus, in the case of the ChAdOx1-S vaccine an adenovirus, to carry a fragment of the genetic information of the SARS-CoV-2 virus into cells at the site of administration, which then synthesize the Spike protein of SARS-CoV- 2. This protein will be recognized by the immune system as foreign to the body and antibodies and cells will be produced to attack it. If later the vaccinated people encounter the SARS-CoV-2 virus, their body will recognize it and be prepared to defend itself.
The adenovirus used to develop AstraZeneca's vaccine does not normally infect humans, is isolated from chimpanzees, and is modified so that it loses its ability to multiply.
As with messenger RNA vaccines, one of the major advantages is the short time required for development and production.
How effective is it and what information is there about protection?
The effectiveness of the vaccine in people who received both doses is calculated at 59.5%, starting 15 days after the administration of the second dose. Protection begins approximately 3 weeks after the first dose of vaccine, but optimal protection may not be achieved until 15 days after the second dose. The duration of protection conferred by the vaccine is under evaluation.
Clinical studies did not allow to estimate the effectiveness in people over 55 years of age. Only 13% of the study participants were over 65 and only 2.8% over 75. The elderly were enrolled later and the small number of COVID-19 cases accumulated up to the time of authorization was not sufficient to allow the calculation of efficacy in this population with certainty. Additional results from ongoing clinical trials may clarify this situation in the future.
What side effects have been observed in clinical trials?
The most commonly reported side effects were:
- pain at the injection site
- Headache
- fatigue
- muscle and joint pain
- fever
- chills
- nausea
Most side effects are mild or moderate and disappear within a few days of vaccination. Compared to the first dose, side effects after the second were milder and less frequent.
What contraindications does it have?
The ChAdOx1-S vaccine is contraindicated for people with known hypersensitivity to one of the substances included in its composition. Also, if an anaphylactic reaction occurs at the first dose, the administration of the second dose is contraindicated. Vaccination is recommended to be postponed for people showing signs and symptoms of acute illness. After vaccination, monitoring for at least 15 minutes is recommended.
How is it administered?
The vaccine is administered intramuscularly and two doses are required for immunization, with the recommended interval between the two doses being 4-12 weeks.
How many doses does it have and how is it stored?
One dose is 0.5 mL and the vaccine will be formulated in vials with 8 or 10 doses, stored at a temperature of 2-8 degrees C, with a shelf life of 6 months."
