More than 28 million Americans fully vaccinated against the coronavirus will have to keep waiting for guidance from federal health officials for what they should and shouldn’t do.

The Biden administration said Friday it’s focused on getting the guidance right and accommodating emerging science, but the delays add to the uncertainty around bringing about an end to the pandemic as the nation’s virus fatigue grows.

“These are complex issues, and the science is rapidly evolving,” Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Friday. “We are making sure and taking time to get this right, and we will be releasing this guidance soon.”

Such guidance would address a flood of questions coming in from people who have been fully vaccinated against COVID-19: Do I still have to wear a mask? Can I go to a bar now? Can I finally see my grandchildren?

The need has slowly grown since January, when the first Americans began to complete the two-dose series of COVID-19 vaccines then available. Now, more than half of people 65 and older have received at least one shot, according to Andy Slavitt, a senior administration adviser on the pandemic.

Experts say it’s understandable that the CDC has been cautious when many scientific questions remain, including how long vaccine-induced immunity lasts, and whether vaccinated people are still able to transmit the virus to others.