Summarised by Centrist
A review in Vaccine journal suggests, beyond preventing a specific disease, non-live vaccines (like COVID-19 mRNA, influenza, hepatitis B, DTaP) have long-lasting nonspecific effects (NSE) affecting mortality and disease susceptibility.
A live vaccine contains a weakened version of the virus or bacteria that can still replicate in the body, imitating a real infection. Non-live vaccines, on the other hand, use parts of the virus or bacteria or their genetic material that cannot replicate to stimulate the immune system without causing an actual infection.
Live vaccines (e.g., oral polio, BCG) are known to generally have more positive NSEs. It is notable that research suggests the order of vaccination matters; giving live vaccines after non-live ones can neutralise negative NSEs.
Despite these findings, health authorities are slow to acknowledge them, and how to measure and understand vaccine NSEs is contentious. Live vaccines are also challenging to produce and may be harmful to severely immunodeficient individuals. COVID-19 vaccines avoid live options due to worries that if someone who got the vaccine came into contact with the actual virus, there might be a risk of creating new virus mutations that could be more dangerous.