DEAR DR. ROACH: If a person has a titanium hip as a result of hip replacement surgery and that person later falls, is it possible that their hip would break? – A.W.

ANSWER: A hip replacement, or total hip arthroplasty, replaces the head and neck of the femur with a prosthesis, which will go into a cup in the hip. Modern materials, such as titanium, are exceptionally light and strong, and it would be extremely unusual to break the prosthesis. However, a fall can still do damage to the hip, such as dislocating the hip, or loosening the prosthesis in the person’s femur. They can also certainly damage or even break the other side, or even the same side in the shaft of the femur. Consequently, it is critically important after a total hip surgery to strengthen the muscles to reduce the likelihood of a fall. Balance exercises provide additional benefit in reducing the chance of a fall. My experience, after decades of taking care of patients before and after hip surgery, is that those patients who put in the extra effort after surgery with physical therapy are those who do the best long term.

DEAR DR. ROACH: I really appreciated your recent explanation of how vaccinations work. However, if the mRNA “tells” the body to start the process that protects against the virus, why don’t they know if people can still get the virus but not get sick and then carry it? – R.Y.

ANSWER: As of the time of this writing, there is much stronger evidence that the mRNA vaccines do prevent people from having an asymptomatic case of COVID-19, which is potentially transmissible. While the data is not conclusive, several lines of study suggest there is a 90% reduction in asymptomatic COVID infections among vaccinated individuals. This is very good news, and with enough people vaccinated, the ongoing community transmission of the virus could stop entirely.

Many people have written me about my advice to get the vaccine for people who have had a case of COVID. One person was so angry, they vowed to destroy my reputation! There is certainly conflicting evidence, with a new study showing high levels of antibodies in (most) people after infection with COVID-19, even after eight months. However, real-world evidence did show that those with a history of COVID-19, and who had positive antibodies, became re-infected with COVID-19 at about the same rate as those who never had a history of the disease. This suggests even survivors of the infection would benefit from getting the vaccine.

Further, public health officials continue to worry about new variants. Epidemiological evidence from Brazil showed far higher levels of re-infection than was thought to be possible after introduction of a new variant into the city of Menaus. Until the transmission rate for COVID-19 is much lower across North America and the rest of the world than it is the day I write this, we still need to continue wearing masks and social distancing in high-risk situations as vaccinations continue to be given to the population.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.