Now that children under the age of 5 are eligible to receive Covid vaccines, almost everyone in the U.S. can get vaccinated against the virus – but some questions still linger for parents of small children.

The U.S. Food and Drug Administration and Centers for Disease Control and Prevention authorized Pfizer's three-dose vaccine series and Moderna's two-dose vaccine series for children under the age of 5 last week. Pfizer's vaccine is for children aged 6 months through 4 years old — the drugmaker already had a vaccine authorized for 5-year-olds — and Moderna's is for kids aged 6 months through 5 years old.

On Tuesday, healthcare workers began immunizing kids under 5 against the virus. Appointments may be limited at first, White House coronavirus coordinator Dr. Ashish Jha told reporters earlier this month, due largely to high initial demand: There are roughly 18 million U.S. children in the age group, and 10 million Pfizer and Moderna doses have been made available for state and local authorities by the federal government.

But Jha said he anticipates that after a few weeks, most parents who plan to vaccinate their children should easily be able to do so. That means you have a little bit of time to figure out the best strategy for your kid's health.

Here's what medical experts say you should know:

Should children under 5 get vaccinated against Covid — and if so, when?

The answer to "should I get my kid a Covid shot?" is a resounding "yes," especially considering the virus' potential fatal effects on young children.

Following the emergence of Covid's omicron variant in December, child hospitalizations skyrocketed and reached a pandemic high. Covid is the fifth-leading cause of death for children between aged 1 through 4 since March 2020, according to a CDC analysis of death certificate data from the National Center for Health Statistics.

And while the vaccines won't offer total protection against Covid infection, they're highly likely to make any symptoms significantly less severe — keeping your child from needing hospitalization.

"There's myths out there, and one is that children don't get seriously ill," says Dr. Jill Foster, a pediatric infectious disease physician at the University of Minnesota Medical School, "But children do get seriously ill, and they are able to spread it to their family members."

It might be tempting to wait until the fall, when the school year starts back up, to get your child vaccinated. That's a bad idea, says Dr. Allen Radner, an infectious disease expert and chief medical officer of Salinas Valley Memorial Healthcare System in California.

"The vaccine isn't 100% effective immediately," Radner says. The Pfizer vaccine series is administered over the course of three months, and the Moderna series over the course of one month. Radner also notes that the longer you wait, the more likely your child is to catch Covid while still unvaccinated and become "sick or seriously ill."

How worried should you be about side effects?

Experts say the Covid vaccine's side effects are relatively minimal and short-lived in small children, especially compared to older children and teenagers. That's good news for parents across the country.

"Overall, younger kids, less than five years, appear to have lower rates of side effects compared to older children and teenagers," says Dr. Karen Acker, a pediatric infectious disease expert at Weill Cornell Medicine and NewYork-Presbyterian Hospital. "That's consistent with what we see for other vaccines as well."

Some common side effects of the vaccines for younger children include pain at the site of injection, fever, fatigue and fussiness. Moderna's vaccines are more likely to cause those side effects than Pfizer's vaccines, according to clinical trial data. Neither vaccine caused any forms of myocarditis — inflammation of the heart wall — in preliminary data.

Still, according to a Kaiser Family Foundation poll from May, only one in five parents of children younger than age 5 said they'd vaccinate their child as soon as the vaccine was made available to that age group. One possible explanation: The idea that the vaccines are pointless, since they're not necessarily preventing people from getting sick.

Acker says this is flawed logic: Unvaccinated people still have a higher risk of getting Covid, and vaccinations are preventing a large percentage of people from severe illness, lowering hospitalizations and deaths across the country.

"You don't know when your child could be next exposed, so the sooner you get your child vaccinated, the sooner they'll be protected," says Acker, "We can't always anticipate when new variants emerge, so I think it's best to be prepared as soon as we possibly can."

Is Pfizer or Moderna better for small children?

Moderna's vaccine series may carry a higher risk of temporary side effects — but its immunity boost kicks in sooner than Pfizer's series, likely due to the doses being given over a shorter period of time, Foster says.

"Both vaccines are very good," Foster says. "The Moderna vaccine does kick in a bit sooner, but preliminary data that we have shows that the protection from the Pfizer vaccine may stick around a little longer."

Preliminary data does give the protection edge to Pfizer: Roughly 75% effectiveness at preventing illness from omicron for children aged 6 months to 2 years, compared to 51% for Moderna's series. For children ages 2 to 4, Pfizer's vaccines were around 82% effective against omicron, compared to Moderna's effectiveness of 37% for kids aged 2 to 5.

But that data may be misleading. "It's difficult because a lot of the Pfizer data was collected before omicron, and for the Moderna data, more was collected after omicron," says Foster. 

Overall, Acker suggests "getting whichever vaccine is available." Either one, she says, will do the job — and do it well.

"What's great about both vaccines is that we know they're both effective at mounting good antibody responses," she says.

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