By Dr. Mallika Marshall

BOSTON (CBS) — Dr. Mallika Marshall is answering your coronavirus vaccine-related medical questions. If you have a question, email her or message her on Facebook or Twitter.

Dr. Mallika is offering her best advice, but as always, consult your personal doctor before making any decisions about your personal health.

Benjamin writes, “Is the booster shot the same as the first shots we got, or is it prepared differently?”

The Pfizer booster is the same formulation and dose as the original shots. The Moderna booster is the same formulation as the original shots but half the dose (50 mcg vs. 100 mcg). You should be able to find either booster right now.

Ralph wants to know, “Is it true that Moderna and other vaccines lose 50 percent of their efficacy in six months?”

It is true that the vaccines lose efficacy over time when it comes to preventing infection, but remain quite effective at preventing hospitalization and death. The Moderna vaccine does seem to be more durable than the others. That said, people over 65 should consider getting a booster after six months for added protection.

Irene asks, “How long does one have to wait for a booster covid shot after getting the flu shot?”

You do not need to wait any time between getting a COVID-19 booster and getting a flu shot.

Ernest says, “I tested positive for COVID and received an antibody transfusion. I am scheduled for a Moderna booster. Should I get it or wait a while?”

You should wait a while. It’s generally recommended that you wait at least 90 days between getting monoclonal antibodies and getting a COVID-19 vaccine. You hopefully got a nice little bump in your immunity from developing a breakthrough infection but you should probably get a booster at some point down the road.

An anonymous viewer writes, “My friend got fully vaccinated then got COVID but she’s telling me she is not contagious and can’t give it to anyone. I am fully vaccinated but am scared.”

Anyone who tests positive for the coronavirus can pass it on to others, even if they’re fully vaccinated. However, after her 10 days of isolation, she should no longer be contagious.

Dr. Mallika Marshall