COVID-19 vaccines provide acquired immunity against SARS-CoV-2, the virus responsible for coronavirus disease 2019. They help the body recognize and fight off the virus, reducing the risk of severe illness, hospitalization, and death. These vaccines play a significant role in public health by mitigating the impact of the global pandemic.
How COVID-19 Vaccines Work
COVID-19 vaccines function by introducing a harmless component of the SARS-CoV-2 virus to the immune system. This component is typically the spike protein, a structure found on the surface of the virus that it uses to enter human cells. The vaccine “trains” the immune system to recognize this spike protein as foreign.
Upon recognizing the spike protein, the body begins to produce antibodies and specialized white blood cells, such as T-lymphocytes and B-lymphocytes. These immune cells are then prepared to quickly identify and neutralize the actual virus if a person is exposed to it. This process allows the body to build protection without experiencing the severe symptoms of a natural infection.
Types of COVID-19 Vaccines
Different COVID-19 vaccines utilize various scientific approaches to achieve immune protection. Messenger RNA (mRNA) vaccines, like those from Pfizer-BioNTech and Moderna, deliver genetic instructions to human cells. These instructions tell the cells to produce the SARS-CoV-2 spike protein, prompting an immune response. The mRNA does not enter the cell’s nucleus or alter DNA, and it is quickly broken down by the body after delivering its instructions.
Viral vector vaccines, such as those from Johnson & Johnson/Janssen and AstraZeneca, use a modified, harmless virus to deliver genetic material from SARS-CoV-2 into human cells. This genetic material then instructs the cells to make the spike protein, triggering an immune response.
Protein subunit vaccines, exemplified by Novavax, contain harmless pieces of the spike protein itself, rather than genetic instructions to make it. These protein pieces, along with an adjuvant to enhance the immune response, are introduced to the body. The immune system then learns to recognize these proteins and generates protective antibodies.
Safety and Common Reactions
COVID-19 vaccines undergo rigorous testing and approval processes to ensure their safety and effectiveness. Their safety continues to be monitored by health agencies. While the development process was accelerated, these vaccines met established safety standards.
Common side effects are generally mild to moderate and typically resolve within a few days. These can include soreness at the injection site, fatigue, headache, muscle aches, and a mild fever. These reactions are a normal indication that the immune system is actively building protection.
More severe adverse events are rare. For instance, anaphylaxis, a severe allergic reaction, occurs at a rate of approximately 5 cases per one million vaccine doses. Myocarditis, inflammation of the heart muscle, and pericarditis, inflammation of the outer lining of the heart, have been reported in rare cases, primarily in male adolescents and young adults after mRNA vaccines, but most individuals recover with rest and simple treatments. Thrombosis with thrombocytopenia syndrome (TTS) was a rare but serious adverse event associated with the Johnson & Johnson vaccine.
Protection Against COVID-19
COVID-19 vaccines provide protection by training the immune system to respond to the SARS-CoV-2 virus. Their primary benefit lies in preventing severe illness, hospitalization, and death from COVID-19. Studies show that vaccinated individuals are substantially less likely to experience these severe outcomes compared to unvaccinated individuals. For example, updated vaccines have reduced the risk of urgent care and emergency department visits.
Vaccination also contributes to reducing the risk of infection and transmission, though the main focus remains on preventing severe disease. Protection from vaccination, like natural immunity, can decrease over time. The virus that causes COVID-19 continuously evolves, leading to new variants that may partially evade previous immunity. This waning immunity and emergence of variants necessitate updates to vaccines to maintain broad protection.
Booster Doses
Booster doses are recommended to enhance and prolong protection against COVID-19. Their purpose is to restore immunity that may have waned since the initial vaccination series or previous infection. Updated vaccines target newer circulating variants, offering broader protection.
The timing for receiving booster doses can vary. Delaying a booster after a recent infection by several months can optimize the immune response. Recommendations for who should receive boosters and their timing are periodically updated based on evolving scientific data and circulating variants.