(CNN) - While it's a bit of a bummer to think about going back to school before it's even the Fourth of July, in many parts of the country, if you want your child to be immunized against Covid-19 by the time classes start, you need to act fast.
Many large school systems -- including Atlanta, Fort Myers, Florida, Flagstaff, Arizona, and the entire state of Hawaii -- start school in the first two weeks of August.
It takes five weeks to be fully vaccinated with Pfizer's vaccine, the only one authorized for adolescents ages 12 to 17. That means, for example, Atlanta students need to get their first shot by July 1 to be fully immunized by the first day of school on August 5.
"Get them vaccinated. Vaccine provides, without a doubt, the best protection against Covid, and we want our schools to be safe and we want our children to go back to school," said Dr. William Schaffner, a longtime vaccine adviser to the US Centers for Disease Control and Prevention. "We have two grandchildren in that age group, and they have been vaccinated, so do not only as I say, but do as my family has done."
Pfizer's vaccine is given in two doses spaced three weeks apart. After the second dose, it takes two weeks until someone is considered fully vaccinated, according to the CDC.
Vaccination for 12-to-15-year-olds started out gangbusters soon after May 10, when the FDA authorized Pfizer's shot for that age group. In less than one week, 600,000 children in that group were vaccinated, according to the CDC.
But the numbers took a nosedive on May 23, the day after media articles appeared about a possible link to the vaccine and myocarditis, or inflammation of the heart, in young people.
The seven-day average of first doses administered to this age group peaked at 220,401 on May 22, the day before the articles. That number dropped to a low of 62,424 on June 20, the most recent day for which data was available.
It turned out the link to myocarditis was real, but most cases have been mild and typically resolved quickly.
Friday, the US Food and Drug Administration added a warning about the risk of myocarditis and pericarditis, inflammation of the tissue surrounding the heart, to fact sheets for the Pfizer and Moderna Covid-19 vaccines.
According to CDC data, out of more than 300 million doses administered, there have been 1,226 preliminary reports of myocarditis, with males ages 12 to 24 having unusually high rates.
That risk pales in comparison with the risks from Covid-19, the CDC says.
Among adolescent boys ages 12 to 17, CDC researchers estimate that for every 1 million second-dose vaccinations, 5,700 Covid-19 cases, 215 hospitalizations, 71 intensive care unit admissions and two deaths would be prevented. It's estimated there might be 56 to 69 myocarditis cases.
Schaffner said he understood that the myocarditis risk might make parents nervous, but that the risk of Covid-19 should make them much more nervous.
"People think that doing nothing is not a decision. But not vaccinating your child is a decision, and it's a decision that puts them at risk," he said.
As of June 24, nearly 1 in 5 children ages 12 to 15 were fully vaccinated, and nearly 1 in 3 teens ages 16 and 17 were fully vaccinated, according to CDC data.
Schaffner and others said they felt the US Department of Health and Human Services hasn't done enough marketing to parents about the importance of Covid-19 vaccination.
"The messaging about Covid vaccination has not been optimal. The federal government moves very, very slowly," said Schaffner, a member of the CDC's Advisory Committee on Immunization Practices.
"I've been talking with other moms, and there just hasn't been much outreach," added Dr. Leana Wen, a CNN medical analyst and former Baltimore health commissioner. "Every Lyft and Uber should have ads. I drive from Baltimore into [Washington] DC and I don't see billboards about vaccination. Why aren't they everywhere?"
On its website, HHS mentions paid TV ads -- such as this one and this one -- targeting parents and teens.
An HHS spokesperson also pointed to a May 26 Facebook town hall about families and vaccination and a toolkit for parents of adolescents to get information about Covid-19 vaccination and help finding a vaccination site.
The spokesperson added that CDC Director Dr. Rochelle Walensky and US Surgeon General Dr. Vivek Murthy hosted a press call with "mommy bloggers" and outlets targeted at parents and women.
Murthy told CNN that on June 16, the government launched a student chapter of the COVID-19 Community Corps.
"Students from around the country are now reaching out peer to peer [to help] other adolescents and young adults understand the facts about the vaccine," Murthy said.