In early 2020, coronavirus, SARS-CoV-2, was identified as the cause of COVID-19. With the rapid spread of infections, the World Health Organization (WHO) declared the outbreak a Public Health Emergency of International Concern (PHEIC) on January 30, 2020. Despite the crucial role of vaccines in saving lives, acceptance of COVID-19 vaccines was initially low in some countries. This hesitancy was primarily due to concerns about vaccine safety and potential side effects.
The Pfizer-BioNTech mRNA vaccine received WHO emergency use listing on December 31, 2020, followed by the Oxford-AstraZeneca adenoviral vector vaccine (ChAdOx1 nCoV-19) on February 15, 2021. The Oxford-AstraZeneca vaccine, developed by the University of Oxford in collaboration with AstraZeneca, uses a modified chimpanzee adenovirus vector to induce immune responses by encoding the SARS-CoV-2 spike protein. Known by various names such as AZD1222, Covishield, and Vaxzevria, the vaccine demonstrated an efficacy of 70.4% with two doses and 64.1% after one dose. This led countries like the UK to authorize its emergency use for adults over 18.
In Iran, the AstraZeneca vaccine was approved for emergency use on February 17, 2021. Subsequent studies confirmed its good safety profile, with common side effects including pain at the injection site, headache, nausea, vomiting, and dizziness. However, rare serious adverse effects like blood clots and anaphylaxis were also reported. Psychological reactions such as Guillain-Barré syndrome, migraine headaches, and nervousness were noted.
A significant cohort study by the Global Vaccine Data Network involving 99 million vaccinated individuals across eight countries revealed important findings. The study confirmed rare safety signals, such as myocarditis and pericarditis after mRNA vaccines (Pfizer and Moderna), and Guillain-Barré syndrome and cerebral venous sinus thrombosis (CVST) following the AstraZeneca vaccine. Notably, there was a statistically significant increase in Guillain-Barré syndrome and CVST within 42 days after the first dose of AstraZeneca. Additionally, increased risks of myocarditis were observed with Pfizer and Moderna vaccines, and pericarditis with the Moderna vaccine and the third dose of AstraZeneca.
The researchers also identified potential safety signals for acute disseminated encephalomyelitis (ADEM) and transverse myelitis with both viral vector and mRNA vaccines.
Recently, AstraZeneca decided to withdraw its COVID-19 vaccine globally due to a surplus of newer, updated vaccines and declining demand for Vaxzevria and Covishield. According to Reuters, the company cited the availability of multiple variant-specific vaccines as the reason for this decision, leading to a halt in the manufacturing and supply of their COVID-19 vaccines.
This journey highlights the complex landscape of vaccine development, acceptance, and the ongoing efforts to ensure vaccine safety and efficacy amidst evolving challenges.