The results of four clinical trials conducted in the United Kingdom (UK), Brazil and South Africa showed that the Vaxzevria vaccine safely and effectively prevented the spread of COVID-19 disease among people over 18 years of age. Approximately 24,000 people were involved in these clinical trials. Half of them received the "Vaxzevria" vaccine and the other half received a vaccine to prevent diseases other than COVID-19. People did not know if they were given a "Vaxzevria" vaccine or an injection of another vaccine.
The safety of the vaccine has been demonstrated in four clinical trials. The Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) supported the calculations on the effectiveness of the vaccine from COV002 study (conducted in the UK) and COV003 study (conducted in Brazil). In the other two studies, fewer than 6 cases of COVID-19 disease were detected, so the number was too low to calculate the effectiveness of the vaccine to prevent disease. Also, as the vaccine should be administered twice and the second dose should be administered 4-12 weeks after the first one, the EMA CHMP focused on data from subjects who were vaccinated according to this standard vaccination scheme.
Studies showed that 59.6% of patients receiving the vaccine did not experience symptomatic COVID-19 disease (68 out of 5494 subjects had symptomatic COVID-19 disease in the "Vaxzevria" vaccine group compared to those receiving another medicine — 164 out of 5438 subjects who had symptomatic COVID-19 disease). This means that the effectiveness of the vaccine as measured in clinical trials is approximately 60%. You can find the latest information about the studies here.
Most of the participants in the above clinical trials were between the ages of 18 and 55. So far, there are not enough results yet to allow EMA to accurately assess the effectiveness of the vaccine in the elderly population. However, in view of the fact that an immune response is observed in the older population, and based on experience with other vaccines, the vaccine is expected to be effective in this population as well. There is also reliable information about the safety of this vaccine in this patient population, which is why EMA experts have decided that the vaccine can also be used to treat the elderly. More information is expected to be obtained in the near future from ongoing clinical trials involving more elderly individuals.