The way I understand vaccines work is that they give the recipient a modified version of a disease which encourages the body to produce antibodies which your body can use in future to fight the real disease should you contract it.
Presumably then, the more vaccinations you get, the more different types of antibodies your body learns/stores. It therefore seems logical that there must be a physical limit to the number of antibodies your body can store in sufficient numbers to be effective. Is this the case? And if so what sort of limit are we talking about? Is it an absurdly high number?
Or have I fundamentally misunderstood how the whole thing works? I admit this might be very possible - I’m a total layman when it comes to this stuff.
No, I don’t think there is a practical limit. People who live in the third world with poor sanitation conditions have immunity to maybe hundreds of pathogens that are not present in a sterile environment in a modern country, which is why travelers so readily get sick when exposed to a new destination. Specific localized antibodies are mostly inherited from the pre-birth womb environment, and new ones are acquired as soon as they are in the outside world.
For example, I am immune to Hepatitis A, which I got as an adult in Ecuador. But Ecuadorenas are all immune to it, because they all had it as a very mild and possibly unnoticed childhood disease, which confers lifetime immunity.
(IANAD, just blowing off a combination of experience and common sense.)
It’s in the millions, so there really isn’t a practical limit. Antibodies have what is called a hypervariable region that allows for a huge number of combinations.
For a trip to a remote area of Peru I once was required to get vaccines or boosters against yellow fever, hepatitis-A, hepatitis-B, influenza, measles, mumps, rubella, tetanus, typhoid, rabies, diphtheria, and polio. (Most were in case we encountered uncontacted tribes who lacked resistance to most diseases.) My upper arms hurt for several days. I also had to take malaria prophylaxis.
Yes I’ve just had a similar number of injections for a trip to Sumatra I’m making next month. Just to point out, I wasn’t asking about a practical limit, although that’s interesting to know of course.
You’ve encountered and gained immunity to more natural antigens than you’ll ever be exposed to in vaccines. I doubt that there’s a practical limit.
I guess the number of needle sticks you could get in a lifetime would be a limit. How many can you get in a day? How many days are in a life? Again, there’s probably not a practical limit.
There seem to be only about 22 different diseases with licensed vaccines in the US (although there may be several versions of vaccines for each one). There are certainly other vaccines that have been tested but not yet approved. But the total number of available vaccines isn’t that great.
Why is the child vaccine schedule so spaced out? I see Hep B at birth and 1 month, then a cluster at 2 mo., influenza at 6 mo., MCV at 9 mo., and another cluster at 1 year. I didn’t include most of the boosters.
When I received a bunch of vaccinations on the same day, I felt feverish for the next day and my arms hurt. I don’t think you would want to do that to a baby.
One reason is that the some diseases you can safely wait until you are a little older. Other diseases might kill you dead before you get old enough if they waited longer. But you want to wait, because (I think?) vaccines are more effective longer if you are a little older.
Another reason is that the fever you get from some vaccinations interfere with the response to some other vaccinations.
The main reason is that a baby’s immune system is immature, and while it can react properly to some vaccines, it cannot to others. The MMR, for example, is given at one year, because that is the age at which enough children become immune from the vaccine to produce herd immunity. There are still a few children who do not become immune at 1 year, but they are few enough, that the 95% necessary for the highly contagious measles and rubella herd immunity is achieved. By the time the booster is given, the response will be very close to 100%, albeit, some people will never have a response, and will always depend on herd immunity. Why this is, is not fully understood, although these people are rare.
If we gave 6-month-olds the MMR, the response might only be 40%, or even lower. If would be a waste of a resource, and a lot of parents would have a false sense of security, and might not be careful about exposing babies to potentially infectious situations, assuming they were protected.
Basically, each vaccine has been studied to see what the heard immunity threshold is for that disease, and then to see at what age giving it to large groups of children produces that threshold immunity. That’s the magic number. The threshold for Hep B may be 80% (I can’t remember, and I made that up-- I just remember that it’s lower than the threshold for measles). Giving it to babies at birth produces either 80% or possibly better herd immunity. Now, some vaccine thresholds may be at 2 months, 3 weeks, and others at 3 months, 12 days, but they are all given at 3 months, because they can be given as a single shot, and the baby has less trauma, parents are more likely to comply if they have fewer visits, and the “12 days” may represent 1/2 a percentage point.
It has nothing to do with a baby “handling” a certain number of pathogens, as a baby breathes in more pathogens in a day than in all vaccines combined.
When I was in the Army, on about the third day of basic training, we all got shots. Because it was possible some people had missed boosters, or never been vaccinated at all, we all got full rounds of the childhood vaccines, plus a couple of others, all within about 2 hours. No one got sick, or even had mild side effects (no one had egg allergies, I guess). No one became autistic. We all had immune systems that could hold titers. People who got stationed overseas got boosters again, plus smallpox, TB, and yellow fever vaccines. All at the same time. Also pneumococcus, a vaccine that didn’t exist yet when I was inducted. They probably also get chicken pox now, as well.
If your body could not handle every vaccine in existence all at once, you could not handle breathing air.
A distinguished vaccine expert, Dr. Paul Offit has noted that a baby’s immune system has the theoretical capacity to handle at least 10,000 vaccines at once. This may sound bizarre, but there’s a sound scientific basis to it. Seeing that infants are bombarded with bacterial, viral, fungal and tons of other antigens from birth, it’s a good thing their immune systems have such a huge capacity.
Antivaxers (who are fond of the bogus “too many too soon” meme), naturally seized on Offit’s remarks to claim that he favored 10,000 (or 100,000) shots for babies, which of course is ludicrous.
The immune system is a parallel system. The B cells involved work independently from one another, which is why the “10,000” limit is a reasonable estimate.
It’s not quite this simple, though. There’s a variety of signalling molecules produced when the immune system is reacting to an antigen such a vaccine. (vaccines may contain pathogens able to replicate but the immune system cannot tell the difference at the molecular level)
Some of these signalling molecules such as cytokines cause the inflammation, fever, etc you get when you are sick. That’s why you can get the same sore throat/fever/headache from even one vaccine shot as you might get from a mild cold. 10,000 doses at once, well, you would expect a proportionally greater response. Too many vaccines at once could cause an immune reaction sufficient to be lethal.
your body is constantly fighting off pathogens, and constantly adapting to fight new ones. we vaccinate against pathogens that cause diseases which are contagious and particularly debilitating or deadly.
it’s only “logical” if you assume the human body is a digital computer which has a fixed dynamic range based on the number of “bits” it can work with. In reality, we are not binary computers, and aren’t constrained to some upper bound.
in many cases, vaccines using killed or weakened pathogens are simply “training” your immune system to identify said pathogens which means later on it’ll get off its ass at the start of infection, rather than letting said pathogen knock you on your ass for a while before walking in and cleaning up the mess.
yes, sometimes a vaccine can provoke mild symptoms which sort of resemble those of the disease they’re supposed to help prevent (witness the people who claim the flu vaccine gave them the flu.) many viral infections- even ones from dead virions in a vaccine- provoke the immune system in an unpleasant way. Rhinoviruses (the ones which cause the common cold) are mostly harmless. The virus doesn’t do much but camp out for a little bit. The nasty symptoms of a cold are due to your immune system going batshit insane.
While in the military, I was on world wide alert/travel status, which meant that I had to be pre-vaccinated for every vaccine that the military had for those regions.
So for some time I would get a bunch of shots every 3 months. As I recall the highest number I received in any one segment was 12 different shots. The only one that really bothered me was the bubonic vaccinations - I would get big lumps in my armpits that lasted for several days and they not only hurt, but were tender and hot.
I am estimating that I had at least 50 vaccinations, but remembering what happened in detail 45 years ago is difficult.
Thanks for replies and insights. I find the herd immunity threshold stuff particularly interesting. It helps reframe the MMR jab debate that happened in the UK recently.
Apparently not. And I say that as a person who’s travel shots book got so full they filled the back cover, when that got full they simply stapled another book to it and carried on merrily.
(Colour me disappointed! I was pretty sure once I’d filled the first book I’d be ‘full up’, as it were, but no such luck!)
There are several things to consider when constructing the pediatric vaccination schedule, but herd immunity is among the least important.
The main consideration is the ability of an infant to respond to the vaccine. For some vaccines, this is greatly influenced by maternal antibodies. If you give the vaccine too early, maternal antibodies might prevent induction of an immune response. If you wait too long for the concentration of maternal antibodies to drop, the infant will be susceptible. One strategy to deal with this problem is to give the same vaccine several times over the course of several months. Another consideration is the risk to the child of the disease. For example, the first measles, mumps, rubella shot is recommended routinely for children aged 12-15 months in the United States (where measles is uncommon), but if the child will travel overseas, vaccination is recommended as early as age 6 months. Another consideration in developing the pediatric immunization schedule is convenience–there is an effort to bunch the immunizations to some extent so that the parent doesn’t have to take the child to the clnic more often than necessary.
