WASHINGTON (Nexstar) — Parents of children under the age of 5 will have to wait a little longer before they find out whether a COVID-19 vaccine will be approved for their children.

Pfizer and the FDA are waiting to see whether 3 doses are necessary for the younger kids, said Jen Kates with the Kaiser Family Foundation.

“This was not about safety of the vaccine at all. I think that the vaccine here is showing to be very safe,” Kates said. “Two just didn’t seem to cut it with the younger kids.”

There are multiple reasons a two-shot vaccine may not be as effective in younger kids. One, their dose is only about a tenth of the size given to adults. And in adults, a new CDC study found protection from a third shot begins to wan after about 4 months.

Still, Kates said, vaccines are worth it.

“They are incredibly effective at preventing people from getting sick, from going to the hospital and from dying,” she said.

Pandemic-related vaccine mandates were the reason truckers and others are protesting at the border crossings from Canada into the United States.

After days of blockades, the Ambassador Bridge between Windsor and Detroit reopened on Sunday.

But tensions are still high. Canadian authorities said they seized ammunition, firearms and body armor from protesters near a crossing between Alberta and Montana.