Moderna is developing eight other vaccines that use mRNA. The company has tested them on animals and 1,700 people and has not found any cases of anaphylaxis or other severe allergic reactions related to the vaccine, said Dr. Jacqueline Miller from Moderna. An anaphylaxis occurred two months after vaccination in a person with a soy allergy. Anaphylactic reactions to vaccines generally occur within minutes or even seconds of the administration of the shots.

Other side effects – fever, chills, fatigue, headache, muscle and joint pain – are much more common after taking the Moderna vaccine, especially after the second shot. While the reported side effects aren’t dangerous, they can be uncomfortable and last one to three days. Doctors say symptoms are similar to those many people experience after taking Shingrix, the vaccine for shingles. People should be prepared to feel under the weather for a day or two after each shot, and may need to take a day off.

Moderna’s study found that 91.6 percent of recipients had sore arms, 68.5 percent had fatigue, 63 percent headache, 59.6 percent muscle pain, 44.8 percent joint pain, and 43.4 percent chills. Some participants also had swollen lymph nodes in the armpit on the side where they received the injection.

Scientists at the company stressed Thursday that the vaccine doesn’t change a person’s genes or interact with DNA, and that mRNA breaks down quickly and doesn’t linger in the body for long.

Both the Moderna and Pfizer BioNTech studies reported a small number of cases of a temporary facial paralysis called Bell’s palsy. Moderna found three cases in the vaccine group and one in the placebo group, and Pfizer had four cases, all in the vaccine group. FDA reviewers didn’t believe the disorder was vaccine-related. On Thursday, Moderna said the company would be monitoring the condition.

The shipping of the vaccine is managed by the Trump administration’s Operation Warp Speed, but each state decides where its doses go. For example, Tennessee plans to distribute most of its expected allocation of 115,000 starting doses over the next week to all 195 local health departments that will vaccinate first responders and to every hospital in the state that hasn’t received a Pfizer shipment this week.

In Kentucky, Governor Andy Beshear told reporters he expected nearly 80,000 doses of the Moderna vaccine in the state’s first shipment, adding, “We will make sure we have some allocation for every acute hospital across the Commonwealth.”