Dear Doctor: Our son will be 3 years old when his baby sister arrives this fall. What can my husband and I do to help him understand the changes that are on the way?

Dear Reader: Congratulations on your growing family, and also on planning ahead for a major change in your son’s life.

At this point, you’ve mastered the baby basics that were probably daunting when your son first came home, such as, well, just about everything. Now you and your husband, along with your toddler, face a new learning curve. You’ll be juggling the care of two young humans at different stages of development, and your son will be coming to terms with his new role as the older -- and no longer only -- child. The steps you take as your pregnancy progresses, as well as how you integrate your new daughter into family life, will go a long way to smoothing the transition.

Start by talking to your son about the coming baby. As a toddler, his ability to grasp either the scope or the details is limited, so use visual examples to help bridge the gap. If someone in your circle of friends and family has a baby, see if you can arrange for your son to meet and spend time with them. (You may have to do this virtually for the time being.) If possible, repeat these visits throughout your pregnancy.

Make a game out of spotting infants when you’re out and about in the world. Get one or two of the many excellent picture books available about the birth of a new sibling and read (and reread) them together. When your pregnancy has progressed enough, let your son feel the baby’s movements. Explain that his new sister can hear him, and encourage him to talk and sing to her. If you’ve decided on a name for your new arrival, use it when talking about her.

This is a great time to break out the family photo album and show your son pictures of you while you were pregnant with him, as well as of his first few months of life. Telling a simple but specific story about each photo will not only help the images become real, it will let your son know he has a solid place in your family’s history.

Pediatricians often recommend buying a life-sized baby doll and using it to practice contact, as well as caregiving activities. Include your son in the preparations for the baby. Toddlers love color and shape and texture, and letting him in on decisions for decor and toys for the new baby’s room will give him a sense of ownership and control. And -- very important -- your husband should be actively involved in each of these steps as well.

Don’t be surprised if your son becomes anxious and clingy as your due date approaches and once the new baby is home. It’s common for young siblings to regress a bit at this point. Just continue to give him love, reassurance and one-on-one private time, and be patient as everyone adjusts to their new roles.

(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: I just read that a coronavirus vaccine won’t be ready until at least next year. How do vaccines work? And why do they take so long to make?

Dear Reader: When measured against the catastrophe of the current pandemic, the estimate of 12 to 18 months to develop and launch a coronavirus vaccine seems like an eternity. But, believe it or not, the proposed timetable is actually extremely fast.

A vaccine is basically a lesson plan that teaches the body how to recognize and eliminate a specific pathogen. It works by introducing the immune system to molecules known as antigens, which are the distinctive sugars and proteins that dot the outer surface of a bacterium or virus. The immune system reacts by sending antibodies to disable or destroy the pathogen. But matching the correct antibody to a brand-new pathogen takes time. So does producing enough antibodies to deal with all of the invaders.

A vaccine gives the body a head start. It presents the immune system with either a harmless form of a virus or bacterium, or with bits of antigens. Each will prompt the immune system to produce the antibodies it needs to attack that particular pathogen. The next time that unique antigen signature is detected, the immune system is ready and able to attack before the pathogen has time to make you sick.

Vaccines can take up to 10 years to develop. That’s due to the multiple phases of rigorous testing it takes to make sure a vaccine is not only effective, but also safe. It begins with work in animal models to understand how both the virus and the vaccine behave in the body. The next step is a Phase I trial, in which the vaccine’s efficacy is tested in a small group of healthy volunteers. This typically takes a year or two, but that may be scaled back to three months for a COVID-19 vaccine.

A larger Phase II trial, which further evaluates the vaccine and involves the use of placebos, usually takes two to three years. For the current vaccine, this may be shortened to eight months.

In Phase III, which also includes placebos, the vaccine is tested on thousands, or tens of thousands, of volunteers. Again, the typical timeline of two to four years is expected to be significantly shortened.

The next step is regulatory review of the clinical process, followed by production and distribution, each of which also take time. Post-approval studies are used to monitor how effective the vaccine is in real-world conditions.

Thanks to previous research into other types of coronaviruses, including those that caused the SARS and MERS outbreaks, scientists have a bit of a head start. They also are using a new and faster technique to develop the vaccine, based on genetic information known as messenger RNA. This has all led to the mid-March launch of a Phase I trial with 45 volunteers at the Kaiser Permanente Washington Health Research Institute in Seattle. It’s a significant first step in what will be a challenging and closely watched process.

(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 8-year-old grandson is coming from Atlanta to spend the summer with us in Idaho. He has asthma, and our daughter has mentioned that my husband and I have to become familiar with his “asthma action plan.” What is that? How should we prepare?

Dear Reader: An asthma action plan is a detailed roadmap for how to manage the disease, including medications and methods for preventing and controlling asthma attacks. It’s necessary because asthma, which is a chronic respiratory disease, is both complex and serious. It can cause symptoms that change not only from day to day but from minute to minute.

For most of us, the act of breathing is effortless. But people living with asthma can never take their next easy breath for granted. The airways of someone who has asthma can suddenly become inflamed and swollen, which makes it difficult to inhale and exhale. This type of chronic inflammation puts their airways on perpetual high alert and makes the tissues liable to overreact to a range of stimuli. These are known as triggers and include dust, pollution, mold, perfumes, smoke, pet dander and other allergens, as well as exertion and even certain weather conditions. Any of these triggers can cause asthma symptoms, which include a wheezing sound when someone breathes, shallow and rapid breathing, sustained coughing fits, labored breathing and weakness or exhaustion.

During an asthma attack, or flare-up, the airways become swollen enough that it becomes very difficult, or even impossible, to breathe. In addition, the groups of muscles that usually help with breathing will tighten up, making getting enough air even more challenging.

The disease is managed with two types of medications -- controllers and relievers. Controllers are typically corticosteroids delivered via an aerosol, which is inhaled. They are used in the day-to-day management of asthma to reduce chronic inflammation, decrease mucus production and relax the bands of muscles around the airways. People with mild asthma may find that this treatment is sufficient to keep the disease under control. Relievers are medications to be used when an asthma attack occurs. They work by swiftly opening up the airways and relaxing the muscles, which either stops the attack or reduces its severity.

Because asthma is both unpredictable and potentially dangerous, it’s important to plan ahead for all eventualities. That’s where the asthma action plan comes into play. It’s a written set of instructions that detail every aspect of an individual’s asthma treatment. This includes potential triggers for an asthma attack, which medications to take, their dosages, their timing and what to do in an emergency. In addition to being familiar with this plan, be sure your local pharmacy has your grandson’s asthma prescriptions on file, and that they include enough refills to last his entire visit. It’s also wise to line up local medical help, in case it is needed.

Some schools and recreational programs require a written asthma action plan on file before allowing a child to attend, so if your grandson will be taking part in any organized activities, be prepared to share the document with them.

Ask your daughter to send you a copy of your grandson’s action plan before he arrives. This will allow you to familiarize yourself with the specifics, and ask any questions you may have well in advance. Or you can find a variety of printable or electronic forms at cdc.gov/asthma/actionplan.html.

(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.)