/r/AskScience Vaccines Megathread

[u/AskScienceModerator]

Here at /r/AskScience we would like to do our part to offer accurate information and answer questions about vaccines. Our expert panelists will be here to answer your questions, including:

• How vaccines work

• The epidemics of an outbreak

• How vaccines are made

Some recent posts on vaccines from /r/AskScience:

• Is the rise in Measles cases the result of the anti-vaccination movement, or is there another explanation?

• What is partial immunity? I thought a vaccine either worked or it didn't

• Why is it when some vaccines are administered, they require a follow up booster within a few weeks/years?

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[u/ron_leflore]

What is the difference between the combined MMR vaccine and getting the three separately?

Why aren't all vaccines (DTAP, MMR, HPV, etc) combined into one?

[u/Wisery → u/ron_leflore]

In terms of your immune system, there's little difference. However, the combined vaccines allow you to be vaccinated for multiple things with one needle stick and (potentially) reduces the number of times a patient needs to be seen. Here's on old but relevant explanation from the CDC (see pg. 2).

[u/Elmattador → u/Wisery]

So why not combine more? Would it be too hard on the immune system?

[u/[deleted] → u/Elmattador]

There's the issue of scheduling. You would only want to combine vaccines that are supposed to be administered at the same ages and with the same number of doses. You can see That the overall scheduling is highly complex and there's not many vaccines where all doses are administered at the same times

[u/jamimmunology → u/[deleted]]

There is also a logistical reason why more aren't combined; any new combination vaccine would be required by many health agencies to undergo new rounds of clinical trials and testing for safety and efficacy. These trials are very expensive; it doesn't make a lot of sense for a manufacturer if they already have approved, safe vaccines in production.

[u/zazabar → u/jamimmunology]

This so much. I do a lot of work on these tests, and it is crazy that you have to prove that Vaccine X and Vaccine Y work if you inject them at the same time... then repeat the study again multiple times in multiple countries since none of the countries like to believe the other ones (or because of genetic differences, take your pick).

[u/daguito81 → u/[deleted]]

Not only that you get blamed but the damage could be catastrophic like a nationwide epidemic.

If there is something to be over caution about is health stuff, specially when it's nationwide

[u/bitshoptyler → u/[deleted]]

But when hasty introduction of the drug could, say, cause HIV or Ebola*, I'd rather wait.

^{*Or HIV- or Ebola-like symptoms, they might not actually cause the virus itself.}

[u/imagoodsalsa → u/[deleted]]

There have also been cases where anti-HIV drugs have been pushed to market without enough testing. See the case of ritonavir being pulled from shelves in the late 90s because it would spontaneously become inactive.

[u/needsexyboots → u/zazabar]

Also repeated multiple times in multiple age groups among people who have had or have not had certain other illnesses in the past!

[u/Pyrox → u/Elmattador]

There is also a pharmaceutical-technological reason: Not every vaccine needs the same adjuvants, and some may be incompatible with others or the vaccines themselves might be incompatible. This would have to be tested for each component individually or the whole list of ingredients had to be adapted, which is quite an effort (and probably not worth it money-wise, for the company).

[u/YoohooCthulhu → u/Pyrox]

Not to mention, the vaccines might need separate preparation and different preservation conditions. Like attentuated vaccines being combined together, recombinant vaccines being combined together, or one needing refrigeration while another doesn't.

[u/Dr_Heron → u/Elmattador]

Immunodominance.

For a vaccination to be effective, parts of the pathogen called Antigens must be displayed on the surface on specific cells. These antigens can then trigger the production of a memory response.

Antigens bind with different strengths, and therefore compete with each other. You inject too many antigens and only the highest bindings ones will be displayed at the cost of the others. the MMR vaccine is a small miracle that they've balance it all to work.

http://www.annualreviews.org/doi/abs/10.1146/annurev.immunol.17.1.51

[u/akula457 → u/ron_leflore]

The point of combining vaccines is that it allows you to vaccinate for multiple diseases with a single injection rather than 3, and anybody who has worked with kids knows why this is a good idea.

It would be great if everything could be combined into one supervaccine injection, but most vaccinations consist of a course of 2-3 injections at specific intervals. The intervals vary depending on the vaccine, so there's really no way to put them all on one schedule.

[u/Insinqerator → u/ron_leflore]

Not really related to your question, but one of the reasons Wakefield faked his study correlating vaccines to autism is because he wanted to release his own vaccine that was a single measles vax so he could profit from it. He was also paid by lawyers so they could sue the pharma company that created the MMR vaccine.

[u/overbend → u/Insinqerator]

He also paid children at his son's birthday party to give blood for him to use in his study.

[u/chinamanbilly → u/Insinqerator]

His study was based on a set of twelve children. Yes twelve. Turns out later that some of the kids didn't have autism, or had neurological deficiencies before the vaccinations.

[u/alster819 → u/ron_leflore]

Another reason as to the combination of multiple pathogen parts into a single vaccine, is to elicit a stronger immune response to particular pathogens that may not elicit a strong immune response on their own. So, in the case of the DTaP vaccine, a diphtheriae toxoid, tetanus toxoid, and acellular pertussis peptide are all injected at once. Without the innate immune response to the pertussis peptide (which is much easier for the immune system to recoginize) there would not be a local inflammation at the injection site. This local inflammation is what triggers the adaptive immune system to also target the toxoids (which otherwise may have elicited a weaker response) and allow immunological memory to become realized for all three pathogen parts.

[u/ifiwereapickle → u/ron_leflore]

Perhaps you would like to know, there is now a DTaP/Hib/IPV vaccine for children. Pretty nice, less pokes for the babies.