Federal regulators are likely to grant emergency approval to the first Covid-19 vaccines for infants and toddlers this week, finally granting protection to roughly 18 million children and closing one of the largest remaining immunization gaps in the population.

But while close to 80 percent of people in the United States have had at least one dose of a Covid-19 vaccine, the vaccination rates have declined sharply in younger age brackets, with children between 5 and 12 with the lowest vaccination rates. So even younger children may prove to be the most challenging group to immunize.

Independent advisers to the Food and Drug Administration are meeting on Wednesday to consider granting emergency use authorizations for Covid-19 vaccines from Moderna and from Pfizer/BioNTech so that young children can get the injections. Moderna is seeking authorization for a two-dose version of its vaccine for children between the ages of 6 months old and 6 years old. FDA advisers already voted unanimously this week to grant Moderna an emergency use authorization of its vaccine for children between 6 years old and 17 years old.

Pfizer/BioNTech’s vaccine, which is already available for kids older than 5, may gain authorization for kids as young as 6 months old, albeit on a three-dose regimen.

The FDA’s analysis of both vaccine trials showed that they are safe and effective at preventing severe disease in their respective age groups. If they get the green light from the FDA and the Centers for Disease Control and Prevention, shots could start going into tiny arms and legs as soon as next week. White House Covid-19 response coordinator Ashish Jha said earlier this month the vaccines could roll out as soon as June 21.

“Our expectation is that within weeks, every parent who wants their child to get vaccinated will be able to get an appointment,” Jha said.

For some families, it’s the culmination of an agonizing wait as the US endured wave after wave of Covid-19 infections. The vaccines are also arriving at a confusing time, in which most people in the United States have received one dose of a Covid-19 vaccine but just over one-third have had a booster dose.

Meanwhile, Covid-19 cases, hospitalizations, and deaths are holding steady at rates far below their peak this past winter. But with more home testing, many Covid-19 cases are not showing up in the official numbers. Summer heat is also forcing people back indoors and subvariants of the omicron variant of Covid-19 are forming a larger share of new infections. The BA.2.12.1, BA.4, and BA.5 subvariants of omicron are more transmissible and are more likely to cause reinfections and breakthrough infections.

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Public health guidance is also changing. In many parts of the country, Covid-19 precautions like mask mandates and social distancing requirements are gone. Regulators have also added to the confusion. The FDA initially considered evaluating the Pfizer/BioNTech vaccine for kids under 5 back in February before deciding to wait for more data following the rise of the omicron variant. According to a Politico report, however, FDA officials also wanted to wait until both the Pfizer/BioNTech vaccine and the Moderna vaccine reported their results in children before evaluating them because they thought it would be simpler and less confusing for the public.

To add further clarity, here are some answers to questions you may have had about Covid-19 vaccines for babies, toddlers, and little kids.

1. Why is vaccinating little kids so critical?

Thankfully, the Covid-19 pandemic has been far less lethal to young children than it has been in adults, and kids are generally less vulnerable to severe disease from the virus.

But “lower risk” is not the same thing as “no risk.” According to the CDC, 442 children under the age of 4 have died from Covid-19 through May 2022. More than 30,000 children in the US have been hospitalized, making Covid-19 more dangerous than influenza in little kids.

“As pediatricians, I think we just we have to make it clear that, while it is true that children don’t typically suffer this disease severely, they can suffer it severely,” said Paul Offit, director of vaccine education at the Children’s Hospital of Philadelphia. “Covid is one of the top 10 killers of children.”

And when an infant or toddler gets sick, they aren’t the only ones affected. Though little kids usually experience mild illness — if they show symptoms at all — a Covid-19 infection can still require a parent or caretaker to take time off work, so a wave of infections in children can take adults out of commission, too.

While most children who get infected do survive, not all of them come out unscathed. Some kids can have lasting symptoms known as long Covid. “We are starting to get a little bit of a sense of long Covid in children, but we are barely scratching the surface,” said Kristin Moffitt, an infectious diseases doctor at Boston Children’s Hospital.

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And scientists are still sussing out all the lingering health effects of the disease on children, whose bodies and immune systems are still developing. One recent study found that Covid-19 can cause hepatitis in children months after the initial infection. With diseases like measles, scientists have observed that early infections can have lifelong consequences. It’s not clear whether that’s the case for Covid-19 in young children.

“We don’t know yet,” Moffitt said. “It will be years before we have the follow-up studies on that.”

2. How well do Covid-19 vaccines work in young children?

The benefits of Covid-19 vaccines for young children are immense and the downsides are minimal.

Pfizer and BioNTech reported last month that their Covid-19 vaccine had 80.3 percent efficacy in preventing Covid-19 cases that produced symptoms in children under 5 years old. Their children’s vaccine uses a 3-microgram dose, one-tenth of the adult dose, spaced out over three injections. The first two doses are three weeks apart and the third is administered two months after the second dose. (Several other vaccines for infants and toddlers are also given as three doses).

The Moderna vaccine for children under 6 years old uses a quarter of the adult dose, 25 micrograms, as two doses spaced 28 days apart. For children between 6 months and two years, the vaccine efficacy against disease was 43.7 percent, falling to 37.5 percent for 2 to 6 year olds.

These efficacies are lower than those reported for the Covid-19 vaccines in adults, but the vaccines are still targeted to the earlier versions of SARS-CoV-2, the virus that causes Covid-19. The clinical trials in children were conducted during surges caused by newer variants including omicron. These variants are better able to evade immune protection from vaccines.

However, Covid-19 vaccines still perform their most vital task in young children, preventing hospitalizations and deaths. In the clinical trials of both vaccines, no cases of severe Covid-19 or fatalities were reported among the kids who received the shots.

The Covid-19 vaccines from Pfizer/BioNTech and from Moderna both appear to be well-tolerated among little kids. Side effects typically include redness, pain, and itchiness near the injection site. Moderna’s vaccine caused more frequent fevers in children under 6 than adults, but they occurred at rates comparable to other early childhood vaccines. In both trials, researchers didn’t see any cases of myocarditis, a rare inflammation of the heart seen in a tiny fraction of older kids who received Covid-19 shots.

Neither vaccine should be given to kids who have a history of severe allergic reactions to any of the ingredients in the shots.

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Moffitt noted that experience with existing vaccines in children shows that complications, however rare, usually emerge within a few weeks of getting the shots, with few long-term negative effects. Additionally, the Pfizer/BioNTech and Moderna Covid-19 vaccines coach the immune system to fight the virus with a molecule called mRNA, which degrades rapidly in the body and is unlikely to cause lingering problems.

“There is no valid biological or scientific reason to expect that there is something lurking that we don’t know yet about these vaccines,” Moffitt said.

The FDA cautioned that it’s not clear yet how long protection from these shots will last. Moderna said that it is already studying the effects of a booster dose in young children. Vaccine manufacturers are also working on versions of their shots targeted to newer variants of Covid-19.

3. Where and when can kids get their shots?

After the FDA’s panel of outside advisors votes on whether or not to recommend the Covid-19 vaccines for little kids, it’s up to the agency to accept the recommendation, which it almost always does.

Then, advisors to the CDC will weigh in on how to administer the shots. Since the dosing for young children is different than that for adults, pharmacies, clinics, and hospitals will have to order fresh batches of the vaccines. Some have already pre-ordered the shots in anticipation of their approval. The vaccines could begin rolling out as early as Tuesday next week, but check with your pharmacy or doctor’s office to make sure the shots are in stock.

“Now, it will take some time to ramp up the program and for vaccines to be more widely available,” Jha said. “We’re going to ship doses out as fast as possible.”

Moffitt added that Covid-19 vaccines do not interfere with other early childhood vaccines, so parents should immunize little kids against Covid-19 as soon as they have the opportunity. And since the Pfizer/BioNTech and the Moderna Covid-19 vaccines both prevent severe illness and deaths with their current formulations, parents should not hold out for vaccines targeted to newer variants.

4. What difference would it make to the pandemic?

While vaccines don’t prevent infection entirely — particularly with the newer Covid-19 variants and subvariants — they do lower the rates of transmission and avert the worst effects of the disease. That will help reduce the overall impact of Covid-19, since children can spread the virus to adults who may be more vulnerable. Keeping people out of the hospital and the morgue is essential to restoring a sense of normalcy.

“The more people you put into that pool of vaccinated people, the fewer people are going to be in the pool of people who can get infected and transmit to others,” Moffitt said.

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But vaccines are only effective if people take them, and that remains a challenge. For kids aged 5 to 11, the Covid-19 vaccination rate has barely topped one-third. “I’m sure when we get to the less than 5 year olds, [uptake] will be less than 30 percent,” Moffitt said. A February poll from the Kaiser Family Foundation reported that 31 percent of parents of kids under 5 years old would vaccinate them when a vaccine is authorized, while 26 percent said they would “definitely not” vaccinate their young children. In such an environment, individual vaccinated children would be protected, but cases could still spike among toddlers and babies, especially as kids go to school.

The virus itself is also changing. Closing infection routes reduces opportunities for mutation, but it doesn’t eliminate them entirely. There may be more changes in store in the weeks or months ahead that could make the virus even more transmissible, evasive, or virulent.

“We all want the pandemic to be over, but we do not know what the pandemic has in store for us,” Moffitt said.