NEW YORK (NYTIMES) - Ms Julie Swann, an engineer who studies health systems and models infectious disease at North Carolina State University, leads a team of researchers who recently tried to simulate how the Delta variant of the coronavirus could move through schools in various scenarios.

The results, which The Washington Post published over the weekend, were alarming.

With absent masking and testing, the study said, more than 75 per cent of susceptible students would become infected in three months. Even with masking and testing, the simulation found, children in environments with low immunity - which includes virtually all elementary school classrooms - had a 22 per cent chance of getting Covid-19 within 107 days.

As a parent of two elementary school students, I found these figures harrowing. It already felt like a gut punch when, last week, Dr Francis Collins, director of the National Institutes of Health, said he did not expect a paediatric Covid-19 vaccine to be approved before the end of the year.

I live in New York City, where school staff must be vaccinated, and mask mandates are relatively uncontroversial. But Ms Swann's team's calculations made it look like my family's chance of getting through this fall without either of our kids coming down with Covid-19 was almost a coin flip.

After talking to Ms Swann, I realise it's not that simple. Her team didn't factor in the effect of quarantining students who test positive, and assumed imperfect mask usage. For many schools, she expects the number of infections to be lower than what the model showed.

That's unlikely, however, to be of much comfort to parents who take Covid-19 seriously but are surrounded by people who don't. With school just beginning and paediatric hospitalisations already higher than ever, they are in an especially intolerable situation.

That's why we need the Food and Drug Administration (FDA) to move quickly. "I can tell you almost certainly there will be data available in September to present to Pfizer," Dr Yvonne Maldonado, a Stanford professor of paediatric infectious diseases and a lead investigator at the Stanford site of Pfizer-BioNTech's paediatric vaccine trial, told me. She thinks Pfizer will be able to file for emergency use authorisation in October.

So why is Dr Collins saying the end of the year? It's unclear. One question, which even well-connected people are having a hard time getting an answer to, is whether the FDA is going to demand extra data for the kids' vaccine.

In July, the agency asked Pfizer-BioNTech and Moderna to double the number of kids in their clinical trials to have a better chance of detecting rare side effects. The FDA also said it wanted four to six months of follow-up safety data, as opposed to two for adults. Most experts don't think this data is necessary for the FDA to authorise the vaccine on an emergency basis.

But we don't know if the FDA will insist on waiting for it. "That is probably one of the decision points that is affecting the various predictions," said Dr Lee Savio Beers, president of the American Academy of Pediatrics.

Two weeks ago, 108 members of Congress, worried about how long approval for a paediatric vaccine was taking, wrote to the FDA seeking some visibility into its timetable. On Monday, the FDA responded, but without offering specifics.

"We understand that it is essential that the public have full trust in the FDA's review process, complete confidence in whatever products we approve or authorise, and faith in FDA and our commitment to protecting public health," the agency said.

Personally, I'm losing that trust. I fear the FDA knows it will be blamed if anything goes wrong with the vaccine, but not necessarily if kids get horribly sick for lack of it.

Even with Delta, kids are far less likely to die than adults. But it's hard to take comfort in that while children's hospital beds are filling up.

In a letter to President Joe Biden, the chief executive of the Children's Hospital Association recently wrote, "With paediatric volumes at or near capacity and the upcoming school season expected to increase demand, there may not be sufficient bed capacity or expert staff to care for children and families in need."

Many parents, convinced that Covid-19 is more dangerous to their children than the vaccine, are going to great lengths to try to get shots for their kids. Some whose younger kids can pass for 12-year-olds are simply lying about their ages.

I'm one of many who has tried, unsuccessfully, to get my paediatrician to give my kids an off-label inoculation, which is technically legal now that the Pfizer-BioNTech vaccine has been fully approved by the FDA. (The American Academy of Pediatrics recommends against this, partly on the grounds that doctors shouldn't be calculating dosages and dosing schedules on their own.)

In addition to modelling diseases for a living, Ms Swann has a 10-year-old who is returning to school. She told me that if her paediatrician agreed to vaccinate her kid off-label, she would do it. "Parents are desperate for it," she said.

The FDA can minimise risk to itself by taking its time. Families don't have that luxury.