On Tuesday, the company confirmed that Moderna vaccine is highly affective and safe for children age 12 to 17 — a finding that could boost supply ahead of the new school year's start this fall.

It would be the second Covid-19 vaccine available for the age group if it is authorized for use, in addition to the Pfizer-BioNTech vaccine.

The company said it plans to ask the Food and Drug Administration to expand the emergency use of its Covid vaccine for teens early next month. If approved, it would likely dramatically expand the number of shots available to middle and high school students ahead of the next school year. Pfizer and German partner BioNTech were cleared to use their vaccine for 12- to 15-year-olds earlier this month, according to CNBC.

“We are encouraged that mRNA-1273 was highly effective at preventing COVID-19 in adolescents,” Moderna CEO Stephane Bancel said in a press release. “We remain committed to doing our part to help end the COVID-19 pandemic.”

The two-dose vaccine, which is given four weeks apart, is already authorized for adults.

The phase 2/3 study the company is citing Tuesday included more than 3,700 adolescents. No cases of Covid were observed in participants who received two doses of the vaccine, while four cases were observed in the placebo group, according to the company.

No significant safety concerns have been identified, and side effects generally are consistent with those seen in an earlier trial of adults, the company said. The most common side effects after the second dose were headache, fatigue, muscle pain and chills, Moderna said.

The new data comes less than three weeks after the company disclosed in an earnings report that early data showed the shot was 96% effective at protecting against Covid in teens ages 12 to 17. That data was based on those who received at least one dose of the vaccine.

The company said Tuesday the shot was shown in the trial to be 93% effective after one dose. Because children are less likely to get seriously ill, Moderna used the Centers for Disease Control and Prevention’s definition of Covid-19 to calculate that figure. It requires only one symptom and a positive Covid test.

U.S. regulators are expected to grant Moderna’s request for use in teens. The approval process could take about a month, just in time for some summer activities and fall classes if Moderna submits the data by early June. Pfizer and BioNTech requested expanded use of their shot in adolescents on April 9, for example, and were authorized by the FDA on May 10.

Vaccinating children is seen as crucial to ending the pandemic. The nation is unlikely to achieve herd immunity — when enough people in a given community have antibodies against a specific disease — until children can get vaccinated, health officials and experts say.

Children make up around 20% of the total U.S. population, according to government data. Some 70% to 85% of the U.S. population needs to be vaccinated against Covid to achieve herd immunity, medical experts say, and some adults may refuse to get the shots. Though more experts now say herd immunity is looking increasingly unlikely as variants spread.

Vaccinating kids may also hasten the return of in-person learning and greenlight after-school extracurricular activities such as sports, art and other in-person activities, health experts say.

Covid-19: Should all children get a vaccine?

One argument for not vaccinating children against Covid is they get relatively little benefit from it.

"Fortunately one of the few good things about this pandemic is children are very rarely seriously affected by this infection," said Prof Adam Finn, who sits on the UK's Joint Committee on Vaccination and Immunisation, BBC reported.

Infections in children are nearly always mild or asymptomatic, which is in sharp contrast to older age groups who have been prioritised by vaccination campaigns.

A study across seven countries, published in the Lancet, estimated that fewer than two out of every million children died with Covid during the pandemic.

Even children with medical conditions that would raise the dangers of a Covid infection in adults are not being vaccinated in the UK at the moment. Only those at "very high risk of exposure and serious outcomes" - which could include older children with severe disabilities in residential care - are recommended to be vaccinated.

The vaccines are incredibly safe, but the risk and the benefit still have to be carefully weighed.

There is another potential benefit to vaccinating children - it could save other people's lives.

This is an approach that is already used for flu. British children aged from two to around 12 are given the nasal spray, largely to protect their grandparents, each year.

One argument is doing the same with Covid vaccines could help contribute to herd immunity - the point at which the virus struggles to spread because so many people are protected.

The Covid vaccines look very good at disrupting the spread of the virus. Just one dose appears to cut the chance of catching the virus by at least half and even those that do still get it are half as likely to pass it on.

Children do not appear to be major spreaders of coronavirus, but older teenagers may still play a role.

"There's certainly evidence of potential for transmission in secondary school ages, so vaccinating could have an impact on overall transmission," said Dr Adam Kucharski, from the London School of Hygiene and Tropical Medicine.

But there is not a universal answer on whether it is worthwhile.

The UK's vaccination programme is hurtling ahead and there have been large outbreaks that have left a legacy of immunity which could also play a role.

More than a quarter of 16 and 17-year-olds in England have coronavirus antibodies in their blood despite barely any of them being vaccinated.

So the UK and similar countries could find they have enough immunity to stop the virus spreading without vaccinating children.

"It's a very different situation to countries without many outbreaks and who don't get as high coverage in adults, then it's very difficult without vaccinating young groups as well," said Dr Kucharski.

Australia is one country struggling with vaccine hesitancy and, alongside places like New Zealand and Taiwan, contained the virus so well there is barely any immunity from infection.