The COVID-19 pandemic necessitated rapid scientific advancements to combat SARS-CoV-2. Vaccines became a powerful tool in controlling the virus and mitigating severe disease. Understanding their scientific principles helps demystify how they provide protection.
Established Vaccine Technologies
Many COVID-19 vaccines adapted well-established technologies to target SARS-CoV-2. Inactivated virus vaccines, like those from Sinovac and Sinopharm, contain whole SARS-CoV-2 particles chemically treated to prevent replication and disease. These inactivated viruses retain their antigenic properties, allowing the immune system to recognize them and develop antibodies against various viral components. Administering these vaccines prompts the body to develop antibodies.
Another established method adapted for COVID-19 was viral vector technology, used by AstraZeneca and Johnson & Johnson. These vaccines use a modified, harmless virus, such as an adenovirus, as a delivery system. The viral vector is engineered to carry genetic instructions for the SARS-CoV-2 spike protein into human cells. Once inside, the host cells use these instructions to produce the spike protein, which then triggers an immune response.
Messenger RNA Vaccine Approach
The messenger RNA (mRNA) approach is a significant advancement, prominently featured in Pfizer-BioNTech and Moderna COVID-19 vaccines. mRNA carries genetic instructions from DNA to the cell’s protein-making machinery. In mRNA vaccines, the mRNA provides instructions specifically for producing the SARS-CoV-2 spike protein.
Upon injection, the mRNA enters muscle cells. These cells then follow the mRNA instructions to synthesize harmless copies of the spike protein. The immune system recognizes these proteins as foreign and generates a protective response. The mRNA does not enter the cell’s nucleus, where human DNA is stored, and cannot alter a person’s genetic code. The mRNA molecules are also fragile and are quickly broken down by the body after delivering their instructions.
How Vaccines Trigger Immunity
All vaccines introduce an antigen to the body, which mimics an infection without causing disease. The immune system recognizes this antigen as foreign and begins a coordinated response. Special immune cells, called antigen-presenting cells (APCs), encounter the vaccine’s antigen, internalize it, and then display fragments of it on their surface.
These APCs then travel to lymph nodes, where they interact with T cells and B cells. Helper T cells become activated and, in turn, help to activate B cells. Activated B cells differentiate into plasma cells, which produce specific antibodies designed to neutralize the pathogen, and also form memory B cells. Additionally, cytotoxic T cells may be activated, which are capable of directly killing infected cells.
This orchestrated response trains the immune system to remember the specific antigen. If the vaccinated individual encounters the actual SARS-CoV-2 virus in the future, the pre-existing antibodies and memory cells can mount a much faster and more effective defense, preventing severe illness or infection.
Rapid Development and Safety Overview
The rapid development of COVID-19 vaccines was a result of several converging factors, rather than a compromise on safety. Decades of research on existing vaccine platforms, including mRNA and viral vector technologies, provided a strong scientific foundation. For instance, mRNA vaccines had been studied for other viruses like influenza, Zika, and rabies, and even in cancer research, before the pandemic.
Unprecedented global collaboration among scientists, governments, and pharmaceutical companies further accelerated the process. Regulatory agencies also streamlined their review processes, allowing for simultaneous phases of clinical trials and continuous data submission, without lowering safety standards. All COVID-19 vaccines underwent rigorous clinical trials involving tens of thousands of participants to assess their safety and efficacy. Post-authorization, extensive pharmacovigilance systems were implemented globally to continuously monitor for any potential adverse events, ensuring ongoing safety surveillance.