CHICAGO (Reuters) - Pfizer PFE.N and BioNTech"s BNTX.O COVID-19 vaccine is safe, effective and produces robust antibody responses in 12- to 15-year olds, the companies said on Wednesday, paving the way for them to seek U.S. and European approval to use the shot in this age group within weeks.The data from a clinical trial, which puts the shot ahead of other Western vaccine developers in the quest to protect children, will likely allow for its use in that group before the next school year, Pfizer Chief Executive Albert Bourla said in a statement. Whether COVID-19 vaccines work and are safe to use on children is one of the big questions drugmakers are trying to answer. Inoculating children and young people is considered a critical step toward reaching “herd immunity” and taming the pandemic, which has killed more than 2.9 million and infected 128.3 million. “I think if we want to get over the pandemic... we really, really need to vaccinate children,” said Dr. Asuncion Mejias, a pediatric physician at Nationwide Children’s Hospital in Columbus, Ohio. Young people have been less likely to suffer severe disease and more likely to have asymptomatic infection, allowing them to unwittingly transmit COVID-19 to others. “Asymptomatic spread is what you are most concerned about,” said Onisis Stefas, chief pharmacy officer at New York-based hospital system Northwell Health. “Those are the people who are most apt to spread.” The Pfizer/BioNTech two-shot vaccine is already authorized for use in people as young as 16. The new study offers the first evidence of how well it will also work in school-age adolescents. In the trial of 2,260 adolescents aged 12 to 15, there were 18 cases of COVID-19 in the group that got a placebo and none among those who received the actual vaccine, resulting in 100% efficacy in preventing the illness, the companies said in a statement. The vaccine was well tolerated, with side effects in line with those seen among participants aged 16 to 25 in the adult trial. The companies did not list the side effects with the latest release. In the adult trial, side effects were generally mild-to-moderate and included injection-site pain, headaches, fever and fatigue. The companies also studied a subset of teens to measure the level of virus-neutralizing antibodies generated a month after the second dose and found it was comparable to study participants aged 16 to 25 in the pivotal trial in adults. Bourla said Pfizer planned to seek expanded emergency authorization from the U.S. Food and Drug Administration “in the coming weeks and ... (from) other regulators around the world, with the hope of starting to vaccinate this age group before the start of the next school year.” Shortly after the data was released Israel, which is leading the world in vaccination rollout, said it would start administering the shot to adolescents if the FDA gives it the green light. MORE DATA Scientists welcomed the news, which has not been published in a medical journal or peer reviewed, but said more data was needed. It will be important to vaccinate younger people to achieve herd immunity, said Dr Peter English, a retired consultant in communicable disease control and former chair of the British Medical Association’s Public Health Medicine Committee. Last week, the companies gave the first vaccine doses in a series of trials testing it in younger children, including those as young as 6-months-old. Rivals are also testing their shots on younger people. A trial by Moderna Inc testing its COVID-19 vaccine in children aged six months to less than 12 years was launched this month. Johnson & Johnson, which recently won authorization for its vaccine in adults, has yet to begin a planned trial here in children. AstraZeneca in December removed children from a mid-to-late-stage trial of its COVID-19 vaccine in Britain. The British drugmaker’s vaccine has been linked this year with a very rare form of blood clotting in the brain, prompting some European countries to halt its use in younger adults even though the cause of the condition remains unclear. Top U.S. infectious disease expert Dr. Anthony Fauci in January raised the prospect of a U.S. vaccination campaign for children by late spring or early summer.