Harris County, following a national call, will pause the administration of the Johnson & Johnson vaccine at county distribution sites.

Harris County Judge Lina Hidalgo tweeted on April 13 that those local residents scheduled to receive the Johnson & Johnson vaccine today at NRG Park will instead be offered the Pfizer vaccine.

This comes as the Centers for Disease Control and Prevention and the Food and Drug Administration advised that Johnson & Johnson vaccinations should be paused after six U.S. women developed blood clots after the injections.

Those clots were observed along with reduced platelet counts — making the usual treatment for blood clots, the blood thinner heparin, potentially “dangerous,” per a joint CDC and FDA statement. One woman died, another was hospitalized. The women were aged between 18 and 48; symptoms presented within 13 days.

The Houston Health Department also announced on April 13 that it will pause the distribution of the Johnson & Johnson vaccine, CultureMap news partner ABC13 reports. No word yet if the distribution pause would affect any scheduled appointments.

Importantly, those receiving vaccines at mobile sites will still receive the Moderna vaccine, ABC13 notes.

Those who received the Johnson & Johnson vaccine and are experiencing adverse symptoms should immediately contact their healthcare provider, the CDC advises.

More than 6.8 million doses of the Johnson & Johnson Vaccine have been administered in the U.S., the vast majority with no or mild side effects. The CDC will meet on April 14 to discuss the cases and the FDA has also launched an investigation into the cause of the clots, ABC 13 adds.

Nationally, the pause will no doubt affect mass vaccination efforts; time will tell how Houston will fare as the U.S. pivots to only two vaccine options for now.