Fwiw, the CDC recommends boosters at least 2 months after the primary series, but Canada and the UK both recommend you wait longer.
From Canada
(Which, i notice, publishes much more detailed and nuanced information than the US CDC.)
NACI continues to recommend that COVID-19 booster doses given as part of the fall program may be offered at an interval of 6 months after a previous COVID-19 vaccine dose or SARS-CoV-2 infection. However, a shorter interval of at least 3 months may be considered particularly in the context of heightened epidemiologic risk, evolving SARS-COV-2 epidemiology, as well as operational considerations for the efficient deployment of the fall vaccine program. Based on what is known at this time about the virus and vaccines, it is not expected that a booster dose will be routinely provided every 3 months.
I read this as "wait at least 6 months for the booster if you don’t think you’ll be at especially high risk, but you can get it after as little as 3 months if you are worried about the likely fall/winter surge in cases. (Or if you are immune compromised, or otherwise at heightened risk.)
The UK is recommending you wait 3 months for your first booster shot, and are only making additional “seasonal” boosters available to those over 50 or at higher risk (either personally, or of spreading covid to those at high risk). They don’t recommend any boosters for kids under 16 unless they have specific health concerns.
If you’re aged 16 or over you can get a 1st booster dose if you:
- have completed your primary COVID-19 vaccination course (1st and 2nd dose, plus an additional primary dose if you have a severely weakened immune system)
- had your previous dose of the COVID-19 vaccine at least 3 months ago
When to get your seasonal booster
If your NHS record shows you’re at high risk from COVID-19, you should be invited for a seasonal booster (autumn booster).
You can have your seasonal booster if it’s been at least 3 months since you had your previous dose.
So, personally, if i had a 12 twelve year old who’d had their second dose less than 3 months ago, i would not be racing to get the booster. I’d wait for at least 3 months to pass.
(Everyone in my household waited more than 3 months after their last booster to get the bivalent booster. But we see a lot of likely risk this fall, and didn’t wait 6 months. We are also older, 2 over 50 and one about 30. )