Both the Houston Health Department and Harris County Public Health will follow a recommendation from federal health agencies that the use of the Johnson & Johnson coronavirus vaccine should be paused.

Harris County Judge Lina Hidalgo said in a tweet Tuesday that administration of the J&J COVID-19 vaccine will be put on hold after a recommendation from both the Food and Drug Administration and the Centers for Disease Control and Prevention.

“Residents who were scheduled to get the J&J vaccine at NRG Park today will be offered Pfizer instead,” Hidalgo said in her tweet. “Mobile sites will be distributing Moderna.”

A tweet by officials at the Houston Health Department said the use of the vaccine will be halted while rare adverse reactions to it are investigated.

Houston Mayor Sylvester Turner said the city primarily uses the Moderna vaccine in its inoculation efforts, so he does not think a pause in the use of the J&J vaccine will cause problems for those who have appointments scheduled.

Dr. David Persse, chief medical officer for Houston, said that there have only been six cases of blood clots reported out of the millions of doses of the J&J vaccine that have been administered across the country. He said none of those cases were in Texas.

“These blood clots appear to be extremely rare,” Persse said.

Turner said that while the reports of clots are concerning, he encouraged people to keep their vaccine appointments.

“I would be more fearful of the virus than I would be of taking, of taking the vaccine,” Turner said. Officials at the federal agencies said the pause is recommended while they investigate reports of blood clots in people who have received the vaccine.