Live vs. Inactivated Vaccines
Live vaccines contain a weakened or attenuated form of a virus or bacteria. They are altered so that they can't cause disease.
The other main type of vaccine is made of the inactivated virus or bacteria (whole vaccine) or just parts of the virus or bacteria (fractional vaccine).
Live vaccines are thought to better simulate natural infections and usually provide lifelong protection with one or two doses. A second dose, like for the MMR vaccine, is given because some people don't respond to the first -- not as a booster dose. Most inactivated vaccines require multiple primary doses and boosters to get the same type of immunity.
Children have been getting live vaccines for some time. In fact, one of the very first vaccines, the smallpox vaccine, was a live-virus vaccine.
Live vaccines include:
- MMR - the combination measles, mumps, and rubella vaccine
- Vavivax - the varicella or chicken pox vaccine
- Proquad - a combination of MMR and Varivax
- rotavirus vaccines - including two oral vaccines, RotaTeq and Rotarix
- Flumist - the nasal spray flu vaccine
- yellow fever vaccine - an attenuated, live-virus vaccine recommended for travelers to high risk areas
- adenovirus vaccine - a live-virus vaccine that protects against type 4 and type 7 adenovirus but which is only approved for military personnel
- typhoid vaccine - the oral typhoid vaccine is made with a live-attenuated strain of Salmonella typhi. An inactivated, injectable version of the vaccine is also available. Either typhoid vaccine would only be given to travelers to high risk areas.
- BCG - the bacille Calmette-Guerin tuberculosis vaccine, which is not routinely used in the United States because it mainly prevents severe TB, which isn't at all common in the United States.
- smallpox vaccine - has not been routinely used since 1972, but is available from stockpiles if it is needed
- oral polio vaccine - the original OPV (Sabin vaccine), which has been replaced in the United States by the inactivated polio vaccine (Salk vaccine)
Although live vaccines don't cause disease in the people who get them because they are made with weakened viruses and bacteria, there is always a concern that someone with a severely weakened immune system could get sick after getting a live vaccine. That is why live vaccines are not given to people who are getting chemotherapy or who have severe HIV, among other conditions.
Whether or not to give a live vaccine to someone who has a problem with their immune system depends greatly on exactly what condition they have and the degree of their immunosuppression, though. For example, it is now recommended that children with HIV get the MMR, Varivax, and rotavirus vaccines, depending on their CD4+ T-lymphocyte counts.
Another concern for parents is whether healthy children should get live vaccines if they will be exposed to someone else who has a problem with their immune system. Fortunately, except for OPV and the smallpox vaccine, which aren't typically used, children who live with someone who has an immunologic deficiency can get most vaccines in the routine childhood immunization schedule, such as MMR, Varivax, and the rotavirus vaccines. That's because it would be rare for someone to contract one of these viruses from someone who got the vaccine. A much bigger concern, actually, would be that the unvaccinated child might get a natural infection with measles or chicken pox, etc., and pass that on to the person with an immune system problem.
Unless they will be in contact with someone who is severely immunosuppressed, such as getting a stem cell transplant and being in a protective environment, they can even get the live, nasal spray flu vaccine.
Viral Shedding and Live Vaccines
Viral shedding, in which someone becomes contagious and can pass a virus to someone else, is sometimes a concern when parents think about live vaccines.
Fortunately, viral shedding is not usually a problem because:
- the MMR vaccine doesn't cause shedding
- the chicken pox vaccine can rarely cause shedding if a child develops a vesicular rash after getting vaccinated, but can be avoided by avoiding direct contact with the rash
- the rotavirus vaccine only causes shedding in stool, so can be avoided with routine hygiene techniques, such as good hand washing, and if immunocompromised people avoid diaper changes, etc., for at least a week after a child gets a rotavirus vaccine
- transmission of the live, nasal spray flu vaccine has not been found in several settings, including people with HIV infection, children getting chemotherapy, and immunocompromised people in health-care settings
And of course, children shed viruses and are truly contagious if they aren't vaccinated and develop any of these vaccine preventable diseases.
What You Need To Know About Live Vaccines
- Although multiple live-virus vaccines can be given at the same time, if they aren't given at the same time, you should wait at least 4 weeks before getting another live-virus vaccines so that they don't interfere with each other.
- It is usually recommended that children who may get a solid organ transplant get up to date on their live-virus vaccines at least 4 weeks before the transplant.
- In addition to children getting chemotherapy, children who are getting daily steroids for 14 days or more should delay getting live vaccines for at least 3 months.
- Live vaccines are reportedly being developed to protect against West Nile virus, RSV, Parainfluenza virus, herpes simplex, CMV, and the Dengue virus.
If you have any concerns about your child getting a live vaccine, especially if your child or someone else at home has a problem with their immune system, be sure to talk to your pediatrician.
CDC. Smallpox Vaccine. http://www.bt.cdc.gov/agent/smallpox/vaccination/vaccine.asp. Accessed Jan 2012.
Encyclopedia of Microbiology (Third Edition), 2009.
Mandell: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 7th ed.;
Red Book. 2009 Report of the Committee on Infectious Disease. American Academy of Pediatrics. 29th Edition.
Tamma, P. MD. Vaccines in Immunocompromised Patients. Pediatrics in Review 2010;31;38.