Moderna's COVID-19 vaccine is 100% effective in children ages 12 to under 18, the company said Tuesday, in announcing results of their latest clinical trials.
In addition to its efficacy, the vaccine showed "no significant safety concerns" in the trial of more than 3,700 adolescent participants, according to Moderna, which said it plans to submit results of the trial to U.S. regulators and request authorization in early June.
COVID-19 vaccine eligibility was widened for children ages 12 and up in the United States earlier this month, when the U.S. Food and Drug Administration (FDA) authorized the Pfizer vaccine for this age group
An independent panel of advisers to the U.S. Centers for Disease Control and Prevention (CDC) then voted May 12 to recommend the Pfizer vaccine for use in children ages 12 to 15.
Moderna's COVID-19 vaccine, along with the Johnson & Johnson vaccine, is already available for anyone 18 years and older in the U.S.
Pfizer, which is currently conducting clinical trials with children as young as 6 months old, has said it will likely seek an emergency use authorization for its vaccine for children ages 2 to 11 in September.
The rapid pace of progress has left parents searching for answers as quickly as the science develops.
Here is what parents may want to know about the COVID-19 vaccines and kids to help them make decisions.
1. What is the science behind the COVID-19 vaccine?
Both the Pfizer and Moderna vaccines use mRNA technology, which does not enter the nucleus of the cells and doesn't alter human DNA. Instead, it sends a genetic "instruction manual" that prompts cells to create proteins that look like the virus -- a way for the body to learn and develop defenses against future infection.
The Johnson & Johnson vaccine uses an inactivated adenovirus vector, Ad26, that cannot replicate. The Ad26 vector carries a piece of DNA with instructions to make the SARS-CoV-2 spike protein that triggers an immune response.
This same type of vaccine has been authorized for Ebola, and has been studied extensively for other illnesses -- and for how it affects women who are pregnant or breastfeeding.
Neither of these vaccine platforms can cause COVID-19.
2. Why do kids need to be vaccinated against COVID-19?
While have not been as many deaths from COVID-19 among children as adults, particularly adults in high-risk categories, kids can still get the virus and just as importantly, they can transmit the virus to adults.
The American Academy of Pediatrics reported this week that children now make up 22.4% of all new weekly cases, and over 3.7 million children have been diagnosed during the pandemic.
"There are really two big reasons why kids need to get the vaccine," explained Dr. Jennifer Ashton, ABC News chief medical correspondent.
"One of them is that it is possible that they could be infected and then unknowingly pass COVID-19 to someone with a serious or underlying, pre-existing medical condition," she said. "And also, though it's very uncommon and unlikely, it is still possible that children infected with COVID-19 could become seriously ill or worse. We have seen that."
"It's important to think in ripple effects, outside the box," Ashton added. "It's not just your home environment that you need to worry about."
3. Will kids experience the same vaccine side effects as adults?
Adolescents experienced a similar range of side effects as seen in older teens and young adults -- generally seen as cold-like symptoms in the two to three days after the second dose -- and had an "excellent safety profile," Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said at a press briefing announcing Pfizer's authorization.
"Based on all this available information, the FDA determined the Pfizer-BioNTech vaccine has met all of the criteria required to amend the EUA, which concluded that the known and potential benefits of this vaccine in individuals 12 years of age and older outweigh the vaccines known and potential risks," Marks said.
Marks encouraged parents who were hesitant to vaccinate their children to speak with their pediatricians, urging confidence in the trial and data.
Moderna said its COVID-19 study with teens ages 12 to under 18 identified no "significant safety concerns." The most common side effects from the vaccine were injection site pain, headache, fatigue, muscle pain and chills, according to the company.
The FDA will scrutinize Moderna's clinical data before authorizing the use in anyone under 18.
4. How effective are the vaccines in children?
Pfizer announced in late March that its clinical trials showed the vaccine was safe and 100% effective in children ages 12-15, similar to the 95% efficacy among adult clinical trial participants.
Marks confirmed on May 10 that after a trial with over 2,000 children, Pfizer found no cases of infection among the children who had been given the vaccine and 16 cases of infection among the children who received a placebo.
No cases of COVID occurred in the 1,005 adolescents that received the vaccine, while there were 16 cases of COVID among the 978 kids who received the placebo, "thus indicating the vaccine was 100% effective in preventing COVID-19 In this trial," said Marks.
Moderna's clinical trial of 3,732 adolescent participants ages 12 to less than 18 years resulted in no cases of COVID-19 in the vaccine group compared to four cases in the placebo group, according to the company.
"We are encouraged that mRNA-1273 was highly effective at preventing COVID-19 in adolescents. It is particularly exciting to see that the Moderna COVID-19 vaccine can prevent SARS-CoV-2 infection," Moderna CEO Stéphane Bancel sad in a statement. "We remain committed to doing our part to help end the COVID-19 pandemic."
5. Will kids get the same dose of the vaccines as adults?
The FDA has authorized the same dosing for 12- to 15-year-olds as adults with the Pfizer two-dose vaccine.
6. What will fully vaccinated kids be able to do?
Children who are fully vaccinated will be able to follow the updated guidance for vaccinated people from the CDC.
That means not wearing a mask while outdoors, except in crowds, and not having to quarantine after known or suspected exposure to COVID-19, according to the CDC.
Kids who are fully vaccinated may also attend small outdoor gatherings with fully vaccinated family, friends, or those who are unvaccinated, and dine at outdoor restaurants with friends from multiple households, according to the CDC.
Being fully vaccinated -- a milestone achieved two weeks after a person's final vaccine shot -- will also make it easier for children to travel internationally and gain entry into concerts or sporting events.
7. Could COVID-19 vaccines impact puberty, menstruation?
There is currently no clinical evidence to suggest the vaccines can have long-term effects on puberty or fertility, according to Ashton, a practicing, board-certified OBGYN.
Ashton noted that while there has been anecdotal discussion of the emotional event of finally receiving the vaccine temporarily impacting menstruation for adult women, the idea of the cause being from the vaccine itself "defies science and biology."
It is really important to understand basic biology here," Ashton said. "Women can have changes in their menstrual cycle and also have gotten the vaccine, that does not mean that one caused the other."
"Right now there is no puberty concern. There is no fertility concern," she added.
8. Will the Johnson & Johnson COVID-19 vaccine be available for kids?
Johnson & Johnson announced in April that it had begun vaccinating a "small number of adolescents aged 16-17 years" in a Phase 2a clinical trial.
As of April, the trial was enrolling participants only in Spain and the United Kingdom, with plans to expand enrollment to the U.S., the Netherlands and Canada, followed by Brazil and Argentina.
9. Where will children access COVID-19 vaccines?
As with the distribution of vaccines to adults, the process of distributing COVID-19 vaccines to children differs by state.
The rollout will be a "multi-pronged approach," including vaccination sites already in operation, major retail pharmacies, mobile health clinics, schools and family doctors, according to the CDC advisory panel.
CVS and Walgreens began giving the Pfizer vaccine to the newly eligible group on May 13, either with scheduled appointments online, through their apps or over the phone.
The Biden administration announced plans to ship Pfizer doses directly to pediatricians' offices, which they have stressed will be an important partner in this effort, encouraging governors to help enroll family practitioners and pediatricians "as quickly as possible."
If a child gets the vaccine at a mass vaccination site or pharmacy, their parent should alert the child's pediatrician's office so they can keep the immunization record up to date.
Both the CDC panel and the American Academy of Pediatrics (AAP) have said it is okay for children to get other vaccines at the same time as the COVID-19 vaccine.
Later this summer, the U.S. Department of Health and Human Services (HHS) will launch "back to school" partnerships to support vaccinations as part of annual physicals and sports physicals.
10. What are health groups saying about COVID-19 vaccines and kids?
The AAP has recommended that "all eligible children, teens, family and household members be vaccinated as soon as possible."
"This is truly an exciting development that allows us to protect a large population of children and help them regain their lives after a really rough year," AAP President Lee Savio Beers, MD, said in a May 12 statement. "As a pediatrician and a parent, I have looked forward to getting my own children and patients vaccinated, and I am thrilled that those ages 12 and older can now be protected. The data continue to show that this vaccine is safe and effective. I urge all parents to call their pediatrician to learn more about how to get their children and teens vaccinated."
"We've seen the harm done to children's mental and emotional health as they've missed out on so many experiences during the pandemic," Beers said. "Vaccinating children will protectthem andallow them to fully engage inall ofthe activities-school, sports, socializing with friends and family- that are so important to their health and development."
11. Are other countries giving COVID-19 vaccines to children?
Yes. Canada's health department authorized the use of the Pfizer-BioNTech COVID-19 vaccine in children 12 to 15 years of age on May 5.
12. Will COVID-19 vaccines be required by schools?
It will be up to each state's government to decide whether a COVID-19 vaccine is required for school entry. Many colleges and universities in the U.S. have announced they will require students to be vaccinated from COVID-19.
ABC News' Sasha Pezenik and Jade A. Cobern, MD, a member of the ABC News Medical Unit, contributed to this report.
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