COVID-19 vaccines have been a major public health tool since their development in 2020-2021.
COVID-19 vaccines are immunizations designed to prevent infection and disease caused by SARS-CoV-2, the virus responsible for COVID-19.
The main vaccines that have been widely used include:
mRNA vaccines: Pfizer-BioNTech and Moderna (use mRNA technology to teach cells to make a protein that triggers an immune response)
Viral vector vaccines: Johnson & Johnson/Janssen, AstraZeneca (use a modified virus)
Protein subunit vaccines: Novavax (contains harmless pieces of the virus spike protein).
These vaccines work by training the immune system to recognize and respond to the virus, primarily by targeting the spike (S) protein that the virus uses to enter human cells.
Vaccination recommendations have evolved as the pandemic has progressed. Generally:
The vaccines are recommended for most people ages 6 months and older
Updated formulations are released periodically to match circulating variants – Recommendations vary by age, health status, and previous vaccination history
The vaccines have been shown to:
Significantly reduce risk of severe illness, hospitalization, and death from COVID-19
Provide some protection against infection, though this wanes over time and varies by variant.
Covid-19 vaccines have a strong safety profile, with serious side effects being rare.
Common mild side effects include arm soreness, fatigue, headache, and sometimes fever for a day or two after vaccination.
mRNA vaccines (Pfizer-BioNTech’s BNT162b2/Comirnaty and Moderna’s mRNA-1273/Spikevax): These contain messenger RNA encoding the SARS-CoV-2 spike protein, which is translated by cells to produce the antigen and trigger an immune response.
The mRNA degrades within approximately 10-20 days and does not modify human DNA.
Adenovirus vector-based vaccines (Johnson & Johnson’s Ad26.COV2.S/Janssen and AstraZeneca’s ChAdOx1) use a modified adenovirus that cannot replicate in humans to deliver the gene for the spike protein into cells.
The viral DNA enters the nucleus for transcription but is not integrated into the host genome.
Protein subunit vaccines (Novavax’s NVX-CoV2373/Nuvaxovid), contain purified spike protein fragments combined with adjuvants to stimulate immune responses.
Inactivated virus vaccines these contain killed whole virus particles that cannot cause infection but can trigger immunity.
High-certainty evidence demonstrates that most authorized vaccines significantly reduce symptomatic COVID-19 infection (vaccine efficacy ranging from 66-98%) and severe or critical disease (efficacy 76-100%).