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.

READ MORE: Coronavirus In Massachusetts: Today's Developments

Mary writes, “I am 74 and had the J&J vaccine. I feel fine, but I’m concerned about this problem with the vaccine. Should I be worried?”

No. Please don’t be worried. The rare blood clot disorder associated with the J&J vaccine is exceptionally rare and seen in younger adults. If you develop severe headache, chest pain, shortness of breath, or leg pain/swelling, contact your doctor. But don’t worry!

Cynthia in Allston is planning to go to the U.K. in September and is worried that the effects of the Pfizer vaccine will wear off before she travels. She wonders if she should get a third dose now as a precaution.

You do not need to get a third dose yet. Booster doses may be better tailored to some of the newer variants than the original vaccine formulations. Immunity from the Pfizer and Moderna vaccines lasts at least 6 months and probably longer, but time will tell if and when a booster shot is needed.

READ MORE: Brookline To Lift Outdoor Mask Mandate On May 21

Rebeca writes, “I am scheduled to have my second vaccine shot on May 3. I plan to travel that weekend so I need to have a COVID test on May 6. What are the chances of having a false-positive given the fact that I would have had the vaccine three days earlier?”

Getting vaccinated will not cause a standard COVID test to turn falsely positive. The tests look specifically for the presence of the virus, not for antibodies.

Erin says, “I have heard that if someone tests positive for COVID-19 but has been fully vaccinated, they do not have to quarantine/isolate. Can you explain why it is considered safe to be around others in this scenario?”

If you test positive for COVID-19, you still need to isolate for 10 days, even if you are fully vaccinated. And you’re right, we still don’t know whether someone who is fully vaccinated could carry the virus and pass it on to others, though the data so far is reassuring.

Charlie writes, “I am a 73-year-old grandfather. I’ve been fully vaccinated for a month. I just learned my 18-year-old granddaughter tested positive today. How soon will I be able to see her?”

MORE NEWS: Moderna Says Vaccine Booster Effective Against South African, Brazil COVID Variants

You’re now well protected against COVID-19 but you should wait until your granddaughter has completed her 10-day period of isolation and is feeling better.

Dr. Mallika Marshall