Experts say it may take years for students to return to the pre-pandemic norms of attending classes without wearing masks, practicing social distancing, and taking other precautionary measures against COVID-19.

They say that employing the trio of hygienic practices, herd immunity, and a coronavirus vaccine is the only way to contain the spread of the virus and ensure safe schooling.

"You're going to need all three moving forward," said Dr. Paul Offit, director of the Children's Vaccine Education Center at the Children's Hospital of Philadelphia, according to CNBC. "If you have a vaccine, you're still going to have to wear a mask and still have to social distance."

Offit said that if a vaccine is developed, which experts predict won't be until at least the end of the year or at least in early 2021, it most likely will be 75% effective. The measles vaccine is 93% effective, according to CNBC. Herd immunity is also not imminent, since you need between 60% and 80% of the population to have antibodies that fight new infections. Experts say that in order to achieve herd immunity, a whopping 196 million Americans would have to become infected, a figure that would push the healthcare system "over the brink."

Dr. Harry Greenberg, a microbiology professor at Stanford University School of Medicine, said that if we get lucky on developing a vaccine, students may be able to return to school without masks in the fall of 2021, according to CNBC.

Pennsylvania's Department of Education recently issued a memo stating that all students over the age of 2 are required to wear face coverings for the entire school day, according to Pennlive.com. The universal mask order allows students to remove their masks while eating or drinking or during an activity made unsafe by the wearing of face coverings. They can also have 10-minute "face covering breaks," according to the memo.