Dear Doctor: I don’t think I’m the only one wondering how the new coronavirus vaccines got developed so fast when other vaccines in the past took so much longer. Can you please explain?

Dear Reader: When the quest for a safe and effective coronavirus vaccine began, early in 2020, we had only previous vaccine development to guide our expectations. And you’re correct, those vaccines -- against diseases such as polio, measles, smallpox and chickenpox -- took years, or even decades, to develop.

Until now, the fastest timeline was the four years it took to develop the mumps vaccine. Yet less than a year into the current effort, two highly effective preparations have received emergency-use approval from the Food and Drug Administration. This is due to multiple factors. A crucial one is international cooperation, which resulted in the immediate sharing of the genetic sequence of this never-before-seen virus. Additionally, the global health crisis prompted abundant funding.

But perhaps most important was the nature of the virus itself. Coronaviruses get their name from the distinctive “crown” of club-shaped spike proteins on their outer surface. Thanks to years of previous research, we know that the virus uses these proteins to enter human cells. Also immensely helpful was the fact that COVID-19 is quite similar to SARS and MERS, each of them coronaviruses that also originated in animals and jumped to humans. In developing the new coronavirus vaccines, scientists were building on an existing body of knowledge.

Unlike previous vaccines, which used a weakened or inactivated virus to trigger an immune response, the new vaccines harness the molecular building blocks of the novel coronavirus. Specifically, they use a single strand of genetic code known as messenger RNA, or mRNA. The genetic code teaches human cells to build a harmless fragment of the spike protein, just enough for the immune system to recognize the coronavirus. This triggers a robust response that deactivates the spike protein. Because that spike protein is how the coronavirus penetrates a cell, disabling it prevents infection. And, because there are multiple ways to deploy mRNA, multiple vaccines are now in different stages of development. That’s also why, when you get the first of the two-dose vaccine regimen, you have to follow up with the same vaccine. You can’t mix and match.

Both approved vaccines have impressive efficacy of 94% to 95%. The numbers are a bit lower for people 65 and older, but it’s believed that may reflect the smaller sample size of clinical trial volunteers in that age group. As with many vaccines, this one has several side effects. Some people receiving the shots report experiencing pain at the injection site, headache, fatigue, pain in the muscles or joints, chills and mild fever. Several people have experienced severe reactions to the vaccine, but those cases were rare.

These new coronavirus vaccines are game-changers. In light of the dangers posed by COVID-19, as well as the lingering effects of the illness, we hope that when the vaccine becomes available to you, you will choose to get immunized.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Our dad is 67 years old and just got a diagnosis of mild cognitive impairment. His doctor told us that getting regular exercise can help. I’ve never heard this before. Is there a scientific basis, or is the idea just for dad to stay healthy?

Dear Reader: Mild cognitive impairment, also referred to as MCI, is a worsening of the skills we use to learn, reason and remember. It affects up to one-fifth of adults over the age of 65. Although, as the name of the condition suggests, the changes to cognition are slight, they are, nonetheless, noticeable. People with mild cognitive impairment are also at increased risk of developing various types of dementia, including Alzheimer’s disease.

An area of study that continues to generate great interest is the beneficial effects exercise may have on cognition and dementia. Research that analyzes years of health and behavior data collected from specific groups of people has found that individuals who exercise regularly can measurably reduce their risk of developing dementia when they age. There is also evidence that these protective effects can carry over to people who continue to exercise in their later years.

A new study, published in November in the journal Alzheimer’s Research and Therapy, found people with MCI who did even a modest amount of exercise each day could be helping to delay the onset of more cognitive decline. Researchers examined health data collected from almost 250,000 people over the course of six years. The majority were between the ages of 65 and 70 and had been diagnosed with mild cognitive impairment. The subjects were divided into four groups: those who never exercised, those who had just begun to exercise, those who had recently quit exercising and those who had exercised prior to their diagnosis and continued to exercise regularly. Each of the groups self-reported the data about their physical activity.

Among the findings was that, when compared to the group that never exercised, those who had exercised prior to and after their diagnosis of MCI reduced their risk of progressing into dementia by 18%. For those study subjects who had begun regular exercise after receiving their diagnosis of MCI, the risk of progressing to dementia decreased by 11%.

When it came to defining physical activity, the researchers set the bar pretty low. They classified it as 10 or more minutes of moderate or vigorous exercise done more than one day per week. Not that surprisingly, they also found that exercising longer and more often conferred increased benefits. The scientists surmised exercise may have protective effects because it raises the levels of certain proteins in the brain, which help with neuron development and maintenance. They also suggested a link to the increase of blood flow to the brain during exercise. When physical activity ceased, so did the positive cognitive effects it conferred.

As with all studies with self-reported data, the conclusions rely on the accuracy of the participants’ record-keeping. Still, the physical and mental health benefits of regular exercise are well known. An exercise program tailored to your dad’s health and abilities could be helpful.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello again, dear readers, and welcome to the first winter edition of our monthly letters column. To those of you who have been sending us questions via the U.S. mail, we’re happy to report that those letters have finally been retrieved. We’ll begin answering soon. But first, we want to address some of the questions we’re getting regarding the coronavirus vaccine.

-- A licensed registered nurse who is in line to get the vaccine soon had a good question: “Today is the first day of the COVID-19 vaccine being administered,” she wrote. “I am scheduled for my second SHINGRIX (against shingles) shot this coming Friday. Should there be a lapse between the two vaccines, or does anybody know?”

The answer to your question isn’t yet clear. But let’s take a look at the common side effects of the coronavirus vaccine, which are pain at the injection site, fatigue, headache, muscle pain, chills, joint pain and mild fever. Some of these overlap with side effects of the SHINGRIX vaccine. In order to differentiate between the two vaccines, and to understand which is the one causing any side effects that you may experience, our recommendation is to separate the two injections by at least a few days.

-- Several of you have written with questions about getting vaccinated when there are existing allergies. “Can a person who is allergic to penicillin and aspirin take the vaccine safely?” a reader asked. When it comes to an allergy to penicillin, or to aspirin or other non-steroidal anti-inflammatories (NSAIDs), the data collected during the clinical trials for the vaccines doesn’t report either as a reason to avoid the vaccine. However, The Centers for Disease Control and Prevention recommends that anyone who is allergic or hypersensitive to any of the components of the vaccine should not receive it. Your doctor, or the vaccine provider, can help you with that information.

Everyone who gets the vaccine should be monitored on-site for at least 15 minutes post-injection. Individuals with a history of severe allergic reactions to any other vaccines, or to other injectable therapies, should consult with their doctors before getting the vaccine. CDC guidelines state that people with a history of severe allergic reactions that are not related to vaccines or injectable medications, such as to foods, pets, venom, or environmental or latex allergies, may still get vaccinated.

When getting the coronavirus vaccine, be sure to disclose any existing allergies; whether you have a fever, are immunocompromised or are on a medicine that affects your immune system; are pregnant, planning to become pregnant or are breastfeeding; and whether you are on a blood thinner or have a bleeding disorder. And if you have already received another COVID-19 vaccine, it’s important to disclose that as well.

-- A reader who is worried about a possible adverse reaction to the vaccine wonders how she will be safe while getting her shot. The answer is that the CDC has asked all vaccination providers to have on hand the appropriate medications and equipment to deal with a possible allergic reaction. This includes epinephrine, antihistamines, stethoscopes, blood pressure cuffs and timing devices to check your pulse.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)