COVID Vaccine Safety: Children, Breastfeeding, Fertility & more

May 20, 2021

The Science Behind COVID-19 Vaccines: Parent FAQs

Many parents have questions about COVID-19 vaccines, which are now available to anyone age 12 and up. The American Academy of Pediatrics answers some of the most common questions from families.

How does the COVID-19 vaccine work?

The COVID-19 vaccine works similarly to other vaccines your child has had. Germs such as SARS-CoV-2, the virus that causes COVID-19, invade and multiply inside the body. The vaccine stops this by teaching the immune system to recognize and make antibodies to fight the virus. After vaccination, your child has less of a chance of getting COVID-19. And if they do get infected with the virus, they may not’ be as sick as they would without the vaccine.

What are the types of vaccines?

Three different vaccines were given emergency use authorization by the U.S. Food and Drug Administration (FDA) so far. Two require two doses (Pfizer and Moderna), and one involves a single shot (Johnson & Johnson).

Distribution of the one-shot vaccine was temporarily paused to look for possible ties to rare but serious blood clots reported during the vaccine’s safety monitoring process. The FDA lifted the pause when data confirmed the chance of developing the clots with the vaccine is extremely low, but continues to monitor the risk.

The COVID-19 vaccines that require two doses are both messenger ribonucleic acid (mRNA) vaccines. The other was developed as a “viral vector” vaccine. They all have the same result — protecting people from COVID-19—but their delivery systems are a bit different.

The vaccine currently available to children and teens over age 12 does not contain any live or dead parts of the virus. Instead, it is made up of nucleic acids, which are the building blocks of all our cells. Once they’ve done their job, they fall apart and exit the body.

How RNA and viral vector vaccines different?

COVID-19 mRNA vaccines carry instructions to our cells to produce harmless pieces of “spike” protein found on SARS-CoV-2. This triggers an immune system response that the body remembers if the virus ever invades.

Although this technology has been studied for decades, widespread use of mRNA vaccines is new. They don’t use the live coronavirus that causes COVID-19. The mRNA in the vaccine gets into the cells where the shot is given. Then it gives the cells instructions on how to create a piece of protein that is found on the virus that causes COVID-19.

Once the protein is created, your immune system identifies it as a foreign molecule. body. The immune process starts, making antibodies that attach to the protein. These antibodies then protect you from getting COVID-19.

Viral vector vaccines, like the mRNA vaccines, also give instructions to your immune cells. Instead of carrying the instructions to your cells on a fat bubble, as with the mRNA vaccine, they are carried in a harmless virus (not the coronavirus that causes COVID-19).

The same process happens as with the mRNA vaccine—the cells create the protein that’s found on the virus that causes COVID-19, the immune system makes antibodies to fight it, and you’re protected from getting COVID-19.

How do we know COVID-19 vaccines are safe for kids?

Before getting FDA emergency use authorization, clinical trials showed COVID-19 vaccines to be remarkably safe and effective for adults and teens age 16 and up. Trials involved tens of thousands of volunteers. After getting additional safety data for younger teens,  the FDA extended authorization to adolescents age 12 and older.  Clinical trials are underway for children as young as six months old.

The vaccines continue to be monitored very closely. In fact, the Centers for Disease Control and Prevention (CDC) say that COVID-19 vaccines will have “the most intensive safety monitoring in U.S. history.”

How effective are the vaccines?

Research shows that all of the COVID-19 vaccines are highly effective at stopping people from getting COVID-19. The vaccines also help prevent serious illness, hospitalization, and death in those who get COVID- 19.

Scientists don’t know how long immunity from the vaccine will protect people. This will become clearer in the future.

How long does it take for the vaccines to create immunity?

It takes around 2 weeks after getting the second dose of the mRNA vaccines for your body to build up an immunity to the virus that causes COVID-19. For the one-dose vaccine, building up immunity takes 2 to 4 weeks.

Do mRNA vaccines change your DNA?

No, the mRNA actually doesn’t interact with your DNA at all. DNA is your genetic material and it’s stored in the nucleus of a cell. The mRNA in the vaccines never gets into the nucleus. And once your immune cells have used the instructions, they break down the mRNA and get rid of it.

Which vaccine should my child get?

Currently, one of the two-dose vaccines (Pfizer) is approved for teens who are 12 to 17 years old. Anyone who is 18 or older should get whichever vaccine is available to them first. This is especially important now with the rise in cases caused by the variant strains of the virus, which seem to be more contagious and continue to spread at alarming rates here in the US and globally. COVID-19 vaccines are free, whether or not you have health insurance.

What about side effects of the vaccine?

COVID-19 vaccines are safe, but there are some short-term side effects your child may experience.  In clinical trials, some adolescents had no side effects, and some had side effects similar to those reported by adults:

  • Pain, redness, and swelling where the injection was given
  • Fever
  • Chills
  • Headache
  • Fatigue
  • Nausea
  • Pain in the muscles

Call your pediatrician and ask about medicines that can reduce these symptoms, which usually go away in a day or so.

While also rare, some people have had serious allergic reactions to the COVID-19 vaccine. This is why your child will need to wait for 15 to 30 minutes after they have a vaccination. If your child has a reaction, there are medications to quickly treat it.

As for long-term side effects, the CDC says this is unlikely. We have years of research and monitoring on other vaccinations that show side effects almost always happen within six weeks of getting a vaccine.

Is it safe to get a vaccine if I’m breastfeeding?

Right now, there’s no evidence that getting a COVID-19 vaccine causes any breastfeeding safety concerns. The American College of Obstetricians and Gynecologists recommends that pregnant and breastfeeding women should be offered the vaccine when they’re eligible.

Can COVID-19 vaccines affect fertility?

​There’s no evidence that any vaccine, including those for COVID-19, causes fertility side effects. The vaccines don’t affect puberty or a child’s reproductive development in any way.  It is safe for pregnant women and anyone who wants to become pregnant in the future.  In fact, among the millions of people now immunized, there are women who got the COVID-19 vaccine while pregnant and women who became pregnant after getting it. Doctors have watched these cases closely, and have reported no safety problems.

​​Were fetal cells used in the COVID-19 vaccine’s development?

None of the vaccines contain fetal cells. All of the vaccines have used fetal cell lines at some point, but there is a difference between fetal cells and fetal cell lines.

Fetal cell lines have been grown in labs since the 1960s. These cells have multiplied, creating generations of fetal cell lines. This means that the cells we have today no longer contain fetal tissue. Several religious groups and bioethics institutes have issued statements and guidance about the COVID-19 vaccines. For instance, the U.S. Conference of Catholic Bishops states that getting vaccinated is morally justifiable given the circumstances. The Charlotte Lozier Institute has information available for those who want to learn more about this topic.

More information


To view the full article by the American Academy of Pediatrics and to find more related links, visit their website.

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