If you're visiting a public space in Philadelphia, you should wear a face mask whether you're vaccinated or not, according to new guidance issued by the Philadelphia health department on Thursday.

Officials said they "strongly recommend" wearing a mask, but stopped short of requiring them. Unvaccinated people are encouraged to double mask to protect themselves and others.

Philadelphia ended its mask mandate on June 11.

A rise of the COVID-19 delta variant has led to an increase in infections across the United States. The highly contagious viral mutation has fueled a threefold increase in new infections over the past two weeks. A majority of new hospitalizations are among people who are younger and have not been vaccinated. Southern states have been hardest hit in the latest wave.

As of this week more than 1 million people have received at least one dose of a vaccine in Philadelphia, Mayor Jim Kenney said in a statement. That total translates to 60.8% of adults being fully vaccinated and 73.9% having received at least one dose, according to the Philadelphia Department of Health. The city opened vaccinations to all residents on April 19.

"We will continue to vaccinate anyone who is ready, and encourage them to join the million-plus people who received this life-saving vaccine in Philadelphia," Kenney said.

Despite being fully vaccinated, someone can still become infected with the coronavirus, but the disease's effects are severely blunted. Vaccinated individuals who acquire a so-called "breakthrough infection" are very unlikely to require hospitalization or die. That's why public health officials worldwide stress the importance of vaccination. (If you still need to be vaccinated, here's a tool to find the closest vaccination provider to your home.)

In addition to the public indoor mask guidance, city officials recommended people avoid crowded indoor spaces.

While Philadelphia is asking people to take new precautions, the city's infection rate is far lower than in previous months.

As of Thursday, 55 people were admitted to city hospitals with COVID-19 and one was on a ventilator. In April 2020, nearly 850 people were hospitalized with severe infections. The city averaged 64 newly reported daily cases over the past two weeks, the health department said. That same average in mid-November 2020 sat at 7,362 positive cases.

Acting Health Commissioner Dr. Cheryl Bettigole said officials are seeing a "small but disturbing increase" in hospitalizations among children with cases doubling as of late.

Currently, the COVID-19 vaccines are not approved for children under the age of 12. Federal health officials said approval may not come until the winter of 2022.

“It's time for all of us to do what we need to do to protect our city's kids. That means  getting fully vaccinated if you haven't yet, and it means all of us going back to wearing masks in public," Bettigole said in a written statement.

Since the pandemic was declared in March 2020, 3,763 Philadelphians have been killed by COVID-19-related illness. Another 146,142 residents contracted the virus, some of whom continue to suffer lingering health effects.

CORRECTION (Friday, July 23, 2021 2:07 p.m.): The Philadelphia Department of Health corrected the number of patients currently hospitalized with COVID-19. This article has been updated to reflect the new data.