From the Guidelines
Live, killed, and attenuated vaccines differ significantly in their composition and how they work in the body, with live/attenuated vaccines providing stronger immunity but carrying risks for immunocompromised individuals, while killed vaccines are safer but may offer less robust protection. The key differences between these vaccine types are:
- Live vaccines contain weakened (attenuated) forms of the pathogen that can replicate but don't typically cause disease, examples include MMR (measles, mumps, rubella), varicella (chickenpox), and oral polio vaccines 1.
- Killed (inactivated) vaccines contain pathogens that have been killed through heat or chemicals and cannot replicate or cause disease, examples include inactivated polio vaccine (IPV), hepatitis A, and most influenza vaccines 1.
- Attenuated vaccines are a type of live vaccine where the pathogen has been weakened in a laboratory setting so it can replicate but has lost its disease-causing ability, and the distinction between live and attenuated is sometimes used interchangeably, though technically all attenuated vaccines are live vaccines 1. Some important considerations for vaccine administration include:
- Live vaccines can pose a risk of uncontrolled infection from the vaccine strain in patients with weakened immune systems and are therefore avoided in these populations 1.
- Killed vaccines are safer for immunocompromised individuals but may require multiple doses to maintain immunity and may provide less robust protection compared to live/attenuated vaccines 1.
- The use of live-attenuated vaccines is generally contraindicated in immunocompromised patient populations due to the risk of uncontrolled viral replication 1.
From the Research
Types of Vaccines
The main difference between live, killed, and attenuated vaccines lies in their composition and the immune response they elicit.
- Live vaccines contain a weakened or attenuated form of the virus, which causes a mild infection and stimulates a strong immune response 2, 3, 4.
- Killed vaccines, on the other hand, contain an inactivated form of the virus, which cannot cause an infection but still stimulates an immune response 2, 3, 5.
- Attenuated vaccines are similar to live vaccines but have been weakened to the point where they do not cause significant disease 2, 4, 6.
Immune Response
The immune response elicited by these vaccines also differs.
- Live and attenuated vaccines tend to induce a stronger immune response, with both systemic and mucosal immunity 3, 4.
- Killed vaccines, while still effective, may not induce as strong of an immune response, particularly at mucosal surfaces 3, 5.
Safety and Efficacy
The safety and efficacy of these vaccines also vary.