# How many different vaccines can be combined into one injection? **URL:** \ **Category:** Factual Questions\ **Created:** [May 4, 2020, 2:37pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126 "2020-05-04T14:37:26Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [May 4, 2020, 2:37pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/1 "2020-05-04T14:37:26Z")
Common vaccine shots include the MMR (measles + mumps + rubella) and TdaP (tetanus + diphtheria + pertussis,) which demonstrate that some vaccines can be combined into one big mixture. What prevents a lot of shots being combined, so you can have a MMR + TdaP + hepatitis + meningitis + polio + several other diseases folded into one single injection? Is it about volume (that each vaccine requires a certain amount of “critical mass” in order to be effective)? Or are they mutually chemical incompatible when mixed together? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 4, 2020, 2:50pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/2 "2020-05-04T14:50:05Z")
I think it’s mostly just that different vaccines are given on different schedules. Some provide short-lasting resistance and need to be re-administered as the resistance wears down, some provide long-term protection but only after a pair of shots given a month or some other interval apart, some work better when administered at certain ages, etc. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 4, 2020, 4:06pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/3 "2020-05-04T16:06:59Z")
And if someone has an allergic reaction to one component it’s more difficult to investigate. Single vaccine injections would need to be prepared for people who are unable to take the multi-shot; and the more vaccines you put in the multi-shot the more people who would be unable to take it. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 4, 2020, 4:10pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/4 "2020-05-04T16:10:50Z")
I had understood that allergic reactions weren’t usually to the payload of the vaccine, but to the various inactive ingredients which are shared between different vaccines. So one would expect all of the different vaccines in a shot to share the same potential allergens. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [May 4, 2020, 4:11pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/5 "2020-05-04T16:11:53Z")
Combination vaccines are more acceptable to parents who want to limit the number of shots their children get, and they’re also helpful in achieving greater compliance with proper scheduling due to less impact of missed appointments. However there are difficulties with coordinating optimal schedules the more vaccines you fold into one shot, and there are potential quality control issues, as discussed [here](http://nature.com/articles/nm0413-382). "_With clear advantages provided by these combination products, and little evidence of added safety risks, the question now being asked by some pediatricians and vaccine manufacturers is: how many diseases can you protect against in a single jab while still eliciting proper immune responses and maintaining adequate safety profiles? “The experience of developing five-fold or six-fold combinations has been that they’re not easy to make,” says Stanley Plotkin, former medical and scientific director of Pasteur-Mérieux-Connaught (now Sanofi Pasteur, based in Lyon, France), who runs a vaccine consultancy in Doylestown, Pennsylvania. “But from a theoretical point of view, there is not yet a limitation on the number of vaccines you could put together in the same syringe.”_ We current have combo vaccines in the U.S. that protect against 5 diseases i.e. Pediarix, which includes DTaP, polio and hepatitis B antigens. In the EU and elsewhere there are shots which cover six separate diseases. More info [here](http://immunize.org/askexperts/experts_combo.asp). ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 4, 2020, 10:17pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/6 "2020-05-04T22:17:47Z")
> [@Jackmannii](#): > > Combination vaccines are more acceptable to parents who want to limit the number of shots their children get, and they’re also helpful in achieving greater compliance with proper scheduling due to less impact of missed appointments. However there are difficulties with coordinating optimal schedules the more vaccines you fold into one shot, and there are potential quality control issues, as discussed [here](http://nature.com/articles/nm0413-382). > > "_With clear advantages provided by these combination products, and little evidence of added safety risks, the question now being asked by some pediatricians and vaccine manufacturers is: how many diseases can you protect against in a single jab while still eliciting proper immune responses and maintaining adequate safety profiles? “The experience of developing five-fold or six-fold combinations has been that they’re not easy to make,” says Stanley Plotkin, former medical and scientific director of Pasteur-Mérieux-Connaught (now Sanofi Pasteur, based in Lyon, France), who runs a vaccine consultancy in Doylestown, Pennsylvania. “But from a theoretical point of view, there is not yet a limitation on the number of vaccines you could put together in the same syringe.”_ > > We current have combo vaccines in the U.S. that protect against 5 diseases i.e. Pediarix, which includes DTaP, polio and hepatitis B antigens. In the EU and elsewhere there are shots which cover six separate diseases. > > More info [here](http://immunize.org/askexperts/experts_combo.asp). On the other hand there are parents who are dubious about vaccines at all and my DIL has convinced a few of her patients to allow half doses a month apart. She will do anything to keep unvaccinated children out of her waiting room. Ultimately, she will “fire” a patient. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [May 4, 2020, 11:05pm UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/7 "2020-05-04T23:05:38Z")
There’s a pneumococcal vaccine that uses 23 different strains, and others that use 13 or 14. > **[Use of 13-Valent Pneumococcal Conjugate Vaccine and 23-Valent...](https://www.cdc.gov/mmwr/volumes/68/wr/mm6846a5.htm)** > > Two pneumococcal vaccines are currently licensed for use in adults in the United States: a 13-valent pneumococcal conjugate vaccine (PCV13 \[Prevnar 13, Pfizer, Inc.\]) and a 23-valent pneumococcal... ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [May 5, 2020, 1:26am UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/8 "2020-05-05T01:26:03Z")
> [@Hari\_Seldon](#): > > On the other hand there are parents who are dubious about vaccines at all and my DIL has convinced a few of her patients to allow half doses a month apart. Is there evidence that a vaccine ‘‘half dose’’ given twice offers full protection? :dubious: Sounds like a really bad idea to me. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [May 6, 2020, 9:22am UTC](https://boards.straightdope.com/t/how-many-different-vaccines-can-be-combined-into-one-injection/853126/9 "2020-05-06T09:22:06Z")
You always get a low-grade immune reaction to a vaccine. That’s the point. It’s never clear how these reactions are going to interfere with each other: will this fever de-activate that other component before it’s effective? Will this element completely co-opt the immune system? Will having the two together make you very very very sick? Is the immunity going to last 5 years or 65? There was actually quite a lot of worry about those combined vaccines when they were first developed. I don’t know if a general theory was ever developed.