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.

Gene writes, “I am fully vaccinated and am planning to donate blood. Do I lose COVID protection when I donate a pint of blood?”

Donating blood after you get vaccinated will not reduce your immunity to the virus. The amount of antibodies which would be removed with a pint of blood is small and shouldn’t have any meaningful impact. Plus, you have “memory” cells in your blood that can make more antibodies if you are exposed to the coronavirus.

Julia writes, “My daughter is in Nairobi and is scheduled to receive the AstraZeneca vaccine on May 26 and then travel to Boston. She is then thinking of getting the Pfizer vaccine. Is it all right for her to mix the vaccines and should she get one or both Pfizer shots after the AstraZeneca?”

There is a study currently underway in the U.K. looking at whether you can mix and match the AstraZeneca and Pfizer vaccines. Preliminary results show that having one then the other is safe, but people are more likely to have mild-moderate side effects with the second shot such as fever, body aches, and fatigue that resolve within a few days. I believe your daughter would only need one dose of the Pfizer vaccine after getting one dose of the AstraZeneca vaccine.

Cheryl asks, “Is it safe for fully vaccinated people from different households to ride in a car together without masks?”

It should be safe for you to ride in a car with other fully vaccinated people without masks on.

Cyndi writes, “I have two children under 16. I am looking forward to the time when they can get vaccinated. Can I register them on the Mass COVID registry in anticipation of their turn even before it is time for them?”

Yes, you can register your younger children at vaccinesignup.mass.gov even before it’s their turn. Kids 12 and up are now receiving notifications through the website that they can go ahead and schedule their appointments.

Sandra writes, “A close member of my family refuses to get vaccinated against COVID. Will he put all of us ‘vaccinated’ family members at risk when we gather during Thanksgiving and Christmas?”

If you’re fully vaccinated, the risk is much greater for him than for you. If any of you are carrying the virus unknowingly, he would be the one who is vulnerable. Maybe knowing that will convince him to get the vaccine.

Dr. Mallika Marshall