what age can babies "fight" illness off? need some advice - Page 4

[mamakay]

Originally Posted by Dymanic

Another reason why this might be viewed as a false dichotomy is that antibody binding properties exhibit a bifurcated nature: they can decrease in fine increments up to a point, beyond which recognition suddenly ceases altogether.

Originally Posted by mahtob

I thought that that was what Mamakay was trying to say all along?

It is.

For example, suppose a child has gotten one dose of the Hib vax. It's not like they're still prone to get Hib ear infections, but not Hib meningitis.
Or if they get Hib meningitis, they're less likely to die from it compared to a totally unvaxed kid.
Each dose either works, or it doesn't.

[dymanic]

Originally Posted by mamakay

According to the evidence, those low levels of antibodies are usually completely ineffective at both preventing the disease and attenuating severity most of the time.

Well, wait. There are many potential "small effects on a cellular level" that will not directly manifest themselves as "levels of antibodies".

Could there be some small effect there that the epidemiology hasn't been sensitive enough to pick up on?

There are small effects that neither the epidemiology nor the serology can reveal. These are both maps; they are analogues to reality, useful in part because they offer a simplified view.

In biology, all kinds of things seem like they should work one way, but then they just don't.

Just as there are many things that appear to be working a certain way, which turn out not to be working that way at all when the observational frame is shifted -- and it is theoretical insights that often suggest new ways to frame, or obtain, the empirical observations.

Each dose either works, or it doesn't.

That's not what Dr. Sears says:

"As a general rule for shots that come in a series, the first dose provides approximately 50 percent immunity, the second dose bumps it up to about 75 percent, and the third dose gives around 90 percent immunity."
http://www.hachettebookgroupusa.com/...erpt25617.html

Originally Posted by Mahtob

in this conversation, we are talking about whether or not immunity is built up, or not.

I think that (whether we realize it or not) we are talking about several different things: specific immunity as a response to antigens in a vaccine, specific immunity as a response to exposure to wild pathogens, and overall immunity as it applies to infants.

But what you appear to be saying is that she is somehow mistaken because we do not know exactly what the threshold is (and perhaps could never know).

Of the three, that's the closest; but it's still not quite what I'm saying. We know what the threshold is, because we arbitrarily pre-defined it; what we don't know is what it means; that is inferred.

But can we assume that if an infant is immune to a disease, then he will not come down with it, and that there is no "partial immunity" that would help him to fight it off, though not completely?

My position is that we can't assume that. But as mamakay herself noted at the outset, this varies from one pathogen to another. For instance, those which require a T-cell independent B-cell response are more difficult for the immature immune system to counter, and with many pathogens, epidemiological patterns reflect a running battle between swarms of antigenic variants and populations of hosts with varying degrees of susceptibility -- degrees which themselves reflect a microcosm of the same battle, one which is not limited to secreted antibodies, and involves multiple lineages of B-cell and T-cell clones with varying degrees of binding affinities and specificities across a range of (frequently overlapping) epitopes, and is surely sensitive to influence by other factors; some genetic, some environmental. Our view of this action is like snapshots of a dimly lit room, taken through a keyhole.

[mamakay]

I don't really know how to respond to most of your post, dymanic. This is seeming increasingly like a game of semantics instead of a fact-based debate, so I'm sort of at a loss.

(I know there will be some crypic response to that, too.)

This:

That's not what Dr. Sears says:

"As a general rule for shots that come in a series, the first dose provides approximately 50 percent immunity, the second dose bumps it up to about 75 percent, and the third dose gives around 90 percent immunity."
http://www.hachettebookgroupusa.com/...erpt25617.html

Are you being serious, or is that your unique sense of humor showing up again?

[EdnaMarie]

I don't have Dr. Sears' book, though I've heard it's good. I'll have to get it from the library when I get to the United States.

Your analogy with the map is not very helpful because it seems like all you are telling us is that we don't know exactly what is going on since we are looking at a map and not reality. Well, duh. None of us understands the human body perfectly and I don't think that anyone is proposing that she can tell this woman exactly what is going on with her particular child at any given moment. However, that does not change the fact that there is or is not a threshold for any given child of a vaccine working due to the way the vaccines work.

Again, with this map analogy it appears that you are confusing what we know with what is actually going on. It is possible to have a theory of what is without being able to verify it. No athiest can prove his theory, but it doesn't mean that he is not correct. What proves he is correct (or not) is the fact of God's non-existence (or existence).

I think that (whether we realize it or not) we are talking about several different things: specific immunity as a response to antigens in a vaccine, specific immunity as a response to exposure to wild pathogens, and overall immunity as it applies to infants.

Well, I for one know what I am talking about. I am talking specifically about immunity as a response to antigens in a vaccine, i.e., how vaccines stimulate an immune response. Overall immunity is, for me, a different question. Not an unrelated one, but a different one. I addressed that in a different paragraph of my answer and I haven't seen that part referred to yet.

If you think that I am not talking about the relevant issues, then perhaps a simple, "The discussion of a threshold oversimplifies the issue because it implies that we can know whether a child is immune or not, and because in fact we are not sure how that threshold is established. However, we know neither of these things, and so we should be very cautious with discussions like this. Among infants, we do not know for sure what the threshold is, and whether they have the tools to use the antigens to fight off disease. So I'd be very careful with taking a little baby out." would do it. Is that what you are trying to say?

Quote:

But what you appear to be saying is that she is somehow mistaken because we do not know exactly what the threshold is (and perhaps could never know).

Of the three, that's the closest; but it's still not quite what I'm saying. We know what the threshold is, because we arbitrarily pre-defined it; what we don't know is what it means; that is inferred.

Let's try this again. Do we believe that there is a natural threshold, or not? Please do not talk about what we believe the threshold is. Do we believe that there is one (a natural one), or do we not? If so, why, and how did we determine what we thought the threshold was?

Our view of this action is like snapshots of a dimly lit room, taken through a keyhole.

Yeah, well, we know even less about Puff the Magic Dragon but most people can definitively say that he either exists or he doesn't. You can talk all you want about our understanding of dragon wings and having arbitrarily defined the difference between dragons and dinosaurs but the fact is, Puff or no Puff.

[mamakay]

Well, I for one know what I am talking about. I am talking specifically about immunity as a response to antigens in a vaccine, i.e., how vaccines stimulate an immune response. Overall immunity is, for me, a different question. Not an unrelated one, but a different one.

Sort of on topic...
Natural immunity does seem to be a spectrum for some of these diseases where the vaccine is an either/or thing.
Hib and Prevnar, in particular (and probably Menactra since it's a similarly engineered vaccine). With natural immunity to Hib and pneumococcus, at no point in life is carriage prevented totally, although as you get older, you carry it for progressively shorter periods of time. This implies a slow build-up of immunity of some kind. Your risk of invasive disease also goes down progressively over the years. (until you get "old" and it starts climbing back up again.)
Surprisingly little is known in terms of hard biology about how it all works, though.

With the vaccine, you don't asymptomatically carry these bacteria. At all. The people that invented the Hib conjugate vaccine were actually shocked by this finding, since that's an effectiveness that no one saw coming. The bacterial conjugate vaccines are really amazing in that regard. (arguments about replacement disease aside).

[EdnaMarie]

With natural immunity to Hib and pneumococcus, at no point in life is carriage prevented totally, although as you get older, you carry it for progressively shorter periods of time. This implies a slow build-up of immunity of some kind. Your risk of invasive disease also goes down progressively over the years. (until you get "old" and it starts climbing back up again.)

Very interesting.

With the vaccine, you don't asymptomatically carry these bacteria. At all. The people that invented the Hib conjugate vaccine were actually shocked by this finding, since that's an effectiveness that no one saw coming. The bacterial conjugate vaccines are really amazing in that regard. (arguments about replacement disease aside).

I'm still waiting for the giardia vaccine. I know that we are like, a million years away because so far even the disease itself does not confer immunity (like malaria) but anyway.