The nation's two largest pharmacy chains are limiting purchases of children's pain relief medicine amid a so-called "tripledemic" of respiratory infections this winter.

Both CVS and Walgreens announced Monday that demand had strained in-store availability across the country of children's formulations of acetaminophen and ibuprofen, both of which aim to reduce pain and fevers.

CVS will limit purchases to two children's pain relief products in CVS stores and online. Walgreens will implement a six-item limit on online purchases (sales at its physical locations are not limited).

"Due to increased demand and various supplier challenges, over-the-counter pediatric fever reducing products are seeing constraint across the country. In an effort to help support availability and avoid excess purchases, we put into effect an online only purchase limit of six per online transaction for all over-the-counter pediatric fever reducers," Walgreens said in a statement.

As for CVS, a spokesperson said, "We can confirm that to ensure equitable access for all our customers, there is currently a two (2) product limit on all children's pain relief products. We're committed to meeting our customers' needs and are working with our suppliers to ensure continued access to these items."

The medicines have been in short supply because of a surge in respiratory infections

Children's pain relievers and fever reducers have been in short supply for weeks as respiratory infections — especially influenza and respiratory syncytial virus, or RSV — have made a comeback as more Americans develop immune protections to COVID-19.

Up to 33 million Americans have already had the flu this season, the CDC estimates, and more than 10,000 cases of RSV were being diagnosed each week through early December (though diagnoses have slowed in recent weeks). Children are more vulnerable than most adults to both the flu and RSV.

Earlier this month, Johnson & Johnson, the company that produces Children's Motrin and Children's Tylenol, said there was no "overall shortage" of the medicine in the U.S. – the empty shelves, rather, were due to "high consumer demand."

On its informational page about treating a child's fever, the American Academy of Pediatrics urges parents "not to panic" if they are unable to find fever-reducing medicine.

"These medicines are not curative. They don't alter the duration of the illness or anything like that. They are essentially purely for comfort," Dr. Sean O'Leary, chair of the Committee on Infectious Diseases for the AAP, told NPR earlier this month. "Fevers from common respiratory viruses in and of themselves are not harmful."

Parents of very young infants should seek medical attention if their children have a fever.