Darnell writes:

Hi Daniel/Vincent,

I was wondering if you could share your thoughts about the mRNA dose for Moderna vs Pfizer for 5 and under.  I believe the Pfizer trials used 1 microgram for 6 months to 2 years and 3 micrograms for 2-5, whereas Moderna used 25 micrograms for this age group.  With the Moderna dosage being even stronger than what Pfizer uses for 5-11 and closer to Pfizer’s dosage for 12-17, I’m wondering if there’s a concern for safety and risk of side effects such as myocarditis.  If there was a choice between a 2 dose regimen of the much stronger Moderna vs 3 doses of Pfizer, what would be your preference?

Thank you,


Ottawa, ON, Canada

Sarah writes:

Hi Daniel,

Thank you so much for these informative and, dare I say, scientific sessions during this pandemic!

I was wondering if you had any information regarding when we might expect a third or “booster” dose of the Pfizer vaccine for the 5-11 year age range. (Especially in light of news of a possible fourth dose for adults, as well as the delay in an EUA for children under 5 years to study a three dose series over only two.)

Thank you!


Sarah E. Greer, MD MPH

Hanover, NH

Gwen writes:

Hello! Thank you so much for the service you provide with these clinical updates!

I am a family physician-turned-brand-new-medical director of a local health department. I was recently asked this question:

“I received 2 doses of Covid vaccine, and then due to complications it was recommended I should not get the booster. Fortunately, I was eligible for Evusheld and have now received 2 doses of that; so my question is, am I considered fully vaccinated and boosted when looking at the Covid flowcharts for exposure; or do I need to follow the guidelines for unvaccinated?”

Our state guidance for quarantine has changed, and is now based on type of exposure rather than vaccination status, so the quarantine question is mostly moot at this point, but the question about how this person should view their vaccination status is a perplexing one. The person stated that they even called Astra Zeneca, but haven’t been able to get a good answer. How should this person view their vaccination status, and what, if anything, would that change in practical terms?

Thank you so much!

Gwen Unzicker MD

Medical Director

Ottawa County Department of Public Health

Victoria writes:

I’m a PA in Gastroenterology, prescribing both immune modulators like Azathioprine and also Biologic agents like Infliximab. Are there any studies on how much these agents increase risk of Covid infection, severity, and long Covid. How about the degree of response to vaccination?

Thanks for your help