Is the need to test different doses of the COVID-19 vaccine in kids versus adults related to differences in body size or weight?

Families/Kids Vaccines

A: No. Testing of different doses in younger kids, compared to teens and adults, is related to potential differences in how the immune system responds to vaccines across different age groups.

When we hear the word ‘dose’, we often think of medications. With medications, a certain level needs to be present in the blood for it to work properly. Those with larger body size tend to need higher doses to achieve the same effect. This is why different medication doses are often prescribed or recommended based on weight.

With vaccines, there isn’t the same dose-response relationship-a smaller dose of vaccine is not automatically needed in kids just because they are physically smaller. Instead, different doses are evaluated in younger age groups incrementally because younger kids tend to mount a stronger immune response compared to older kids and adults. This variation in immune response is due to differences in the composition and maturity of immune cells and not because of differences in size or weight.

Overall, the main goal of the trials ongoing in younger kids is to identify the dose needed to trigger an adequate immune response in each age group, while minimizing side effects and maximizing safety. The lack of connection between vaccine dose and physical size is also why your 9-year old that happens to be the same size (or larger) as your 12-year old, can’t just get the vaccine authorized for kids aged 12-15 years. Sorry younger sibs, hopefully soon!

As trial results become available for younger kids, including information on whether dosage might differ across age, we Nerdy Girls will provide more updates!

For thoughts on this topic from our Nerdy friend Dr. Alison Bernstein of Mommy, PhD skip to minute 4:00 on our FB live Q&A from this morning.

For more information on rationale for evaluating differences in vaccine doses in kids, see here:

Nature: COVID vaccines and kids: five questions as trials begin

Miami Herald: Will kids get the same Pfizer COVID vaccine dose as adults? Here’s what to know

Our latest post on vaccine trials in kids aged < 12 years

Link to original FB post