olddrummerdude
New member
@aussiewife I would say the same reason a 90 pound woman and a 500 pound man can both get the same flu shot and it be just as effective.
Looking for reassurance. Can anyone explain why a 40 pound 4-year-old can get the same covid vaccine as a 15 pound 6-month-old?
- Thread starter aussiewife
- Start date
@aussiewife If you haven't already, this article is super informative, particularly about the concern between pfizer and Moderna and side effects. (Honestly I've been following this epidemiologist the whole pandemic, she has been an amazing science based resource).
In terms of your 6 month and 5 year old scenario. Our bodies immune systems develop as we age, weight has nothing to do with it. (For example, a baby is a preemie and underdeveloped due to their gestational age, but you can have a preemie baby that's a larger weight than a normal baby). You dose per weight for most drugs because volume of distribution (ie, drugs moving to different compartments in the body, like fat vs muscle vs interstitial fluid vs protein bound) had to be considered to get enough drug hitting enough of the right receptors. Vaccines are different in that they just trigger your bodies natural immune response to a virus, so we just have enough "dose" injected into a muscle, the immune cells recognize it right away and start doing their thing. We dont have to worry about the vaccine moving into fat or being metabolized by the liver, etc. Like another commenter said, adults all get the same dose regardless of size. I will add that elderly sometimes get different doses of vaccines because again, your age changes your bodies immune response. The only different thing we might consider for a person's weight is needle size to ensure it reaches the muscle.
In terms of your 6 month and 5 year old scenario. Our bodies immune systems develop as we age, weight has nothing to do with it. (For example, a baby is a preemie and underdeveloped due to their gestational age, but you can have a preemie baby that's a larger weight than a normal baby). You dose per weight for most drugs because volume of distribution (ie, drugs moving to different compartments in the body, like fat vs muscle vs interstitial fluid vs protein bound) had to be considered to get enough drug hitting enough of the right receptors. Vaccines are different in that they just trigger your bodies natural immune response to a virus, so we just have enough "dose" injected into a muscle, the immune cells recognize it right away and start doing their thing. We dont have to worry about the vaccine moving into fat or being metabolized by the liver, etc. Like another commenter said, adults all get the same dose regardless of size. I will add that elderly sometimes get different doses of vaccines because again, your age changes your bodies immune response. The only different thing we might consider for a person's weight is needle size to ensure it reaches the muscle.
katrina2017
New member
@sharrylee
Slightly tangentially, but preemies get their vaccines based on actual age and not gestational age. You can have very small preemies getting their first vaccines before leaving NICU and technically before they are 0 days old by gestational age. This would be the same vaccine dose given to other babies. It's been a while, but I recall the reasoning being that they begin getting exposed to environmental antigens the moment they are born, so immune system development starts from that time, not gestational age.
Slightly tangentially, but preemies get their vaccines based on actual age and not gestational age. You can have very small preemies getting their first vaccines before leaving NICU and technically before they are 0 days old by gestational age. This would be the same vaccine dose given to other babies. It's been a while, but I recall the reasoning being that they begin getting exposed to environmental antigens the moment they are born, so immune system development starts from that time, not gestational age.
@katrina2017 Good to know! That's cool and totally makes sense! I was mostly just using preemies as an example of weight not being an indication of body/life stage.
heismerciful
New member
@sharrylee Just came to say that I love YLE and she too has been an abundance of information for me as well ! I actually will share her work more sometimes than even the CDC because I think her posts are more accessible for patients.
@heismerciful Agreed! She explains and translates the information so well and so quickly! I would reccomend her to patients all the time.
beeman2014
New member
@sharrylee +1 for YLE!! I am not a parent but stumbled across this sub and saw this top question so I blurted "it's because of the maturity of the immune system!" which I learned from following Dr. Jetelina. 
From the 5-11 vaccine post, but same concept:
From the 5-11 vaccine post, but same concept:
@aussiewife My toddlers got the moderna vaccine at 1 and 3 yo and we had no idea if they got placebo or real vaccine until we were unblinded just two days ago since they had 0 side effects.
@aussiewife Others have touched on your main question, but for the point about infection, the vaccine wouldn’t cause a nasal test to come up positive so you could do that if you get worried about a coincidental infection. Technically the test isn’t valid for
@sabresong From what I have read, no side effects at all is actually not the most likely scenario, at least with moderna. But your point #2 is spot on, iirc something like 60% had a sore arm. About 25% had a low grade fever. This actually might be lower frequency than adults have. I consider this a fully acceptable trade off for my kid.
Less than 1% of participants developed a fever higher than 104F, if you’re concerned about having to rush to the hospital.
Less than 1% of participants developed a fever higher than 104F, if you’re concerned about having to rush to the hospital.
@aussiewife I asked my child’s doctor the same question . The reason is because of how developed the immune system is by a certain age. The weight of the child doesn’t matter, it’s just how the immune system works at different ages. This is why they had to test different age groups. A child is not just a mini adult. The immune system is not fully developed yet. They broke the trials down to smaller groups because the immune system changes as we age.
The adult vaccine is the same vaccine whether your 400lbs or 120lbs. Vaccines aren’t dependent on weight.
Edit to add anecdote for your final question… I got Covid 2 days after my booster shot. It was very mild and just a cough for a few days. It seems unlikely that your baby will catch it right after getting the shot and if they do I don’t think it matters.
The adult vaccine is the same vaccine whether your 400lbs or 120lbs. Vaccines aren’t dependent on weight.
Edit to add anecdote for your final question… I got Covid 2 days after my booster shot. It was very mild and just a cough for a few days. It seems unlikely that your baby will catch it right after getting the shot and if they do I don’t think it matters.
@aussiewife Drugs are dosed by weight because the drug itself has the therapeutic benefit. Vaccines are just a trigger to get your immune system to create its own therapeutic benefits, and your immune system (and your daughter’s) is the right size for your/her body. You don’t need a bigger trigger for a bigger body at the same developmental stage.
sarahsknight
New member
@aussiewife I’m 120 lb, my husband is 230 lb, and we have gotten all the same exact COVID vaccines… and also haven’t gotten COVID (knock on wood).
It’s the same with other vaccines we’ve both had to get at the same time - flu shots, Tdap… the vaccine dosage isn’t dependent on our weight or size.
It’s the same with other vaccines we’ve both had to get at the same time - flu shots, Tdap… the vaccine dosage isn’t dependent on our weight or size.
iowakid8401
New member
@aussiewife I just want to speak to the fever issue, but obviously this is purely anecdotal.
My son is in the Moderna trial. He turned 1 the day after his first dose, and was 13 months for his second dose. For the trial, we had to take his temperature and record info about his demeanor every day for a week after each dose, plus check in periodically about any doctor visits or illnesses. We do check-ins 6 months later, and are just waiting for info on the booster trial. Just found out he got the real thing, not the placebo. He did get a low grade fever after dose 2, but it stopped out at 99.5 degrees, and we only even caught it because we had to take his temp so often. He was a bit cranky the next day, but not much worse than a day he takes a crappy nap. Every trial parent I have spoken to has had either a super similar experience, or their kid had no symptoms at all.
My son is in the Moderna trial. He turned 1 the day after his first dose, and was 13 months for his second dose. For the trial, we had to take his temperature and record info about his demeanor every day for a week after each dose, plus check in periodically about any doctor visits or illnesses. We do check-ins 6 months later, and are just waiting for info on the booster trial. Just found out he got the real thing, not the placebo. He did get a low grade fever after dose 2, but it stopped out at 99.5 degrees, and we only even caught it because we had to take his temp so often. He was a bit cranky the next day, but not much worse than a day he takes a crappy nap. Every trial parent I have spoken to has had either a super similar experience, or their kid had no symptoms at all.
@iowakid8401 Medical perspective, we don’t consider low grade fevers a thing. We consider a fever to start at 100.4f or 38c (am an ED nurse)
@msrathore I’m sure in the ER a low grade fever isn’t noteworthy but for clinical research all data should be considered. The temperature isn’t problematic in and of itself but does indicate an immunological response.
@prepper72 Well you should expect an immune response to a vaccine. But you have to draw the line somewhere and if you're looking for adverse effects, you should probably wait until its actually an adverse effect before counting it.
aussiewife
New member
@iowakid8401 Thank you! That is comforting