A Johnson & Johnson logo is seen in this photo image in front of a medical syringe and vial of coronavirus vaccine.

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Headache, fatigue, and muscle aches were some of the most common side effects in people who received Johnson & Johnson’s one-shot coronavirus vaccine in clinical trials, according to a Food and Drug Administration report released Wednesday.

In the report, FDA staff endorsed J & J’s vaccine for approval for emergency use. If approved, it would be the third vaccine approved in the US after Pfizer-BioNTech and Moderna.

Post-vaccination side effects are common, doctors say, and usually signs that they are helping to protect against the disease. The FDA determined that the clinical trial results and safety data “are in accordance with the recommendations in the FDA guidelines on emergency approval of vaccines to prevent COVID-19.”

The most common, least severe “local” side effect among vaccinated subjects was injection site pain, which was reported by nearly half of vaccine recipients compared with about 17% in the placebo group. Skin redness or erythema and swelling were reported less frequently, the FDA said.

The most common “systemic” side effects, typically less common than local reactions but more serious, were headache and fatigue, according to the report. Almost 40% of people who received the vaccine said they had a headache, and only more than 38% said they felt tired.

More than 33% of people vaccinated said they had muscle pain, around 14% reported nausea, and under 10% had a fever, according to the report. Most of the side effects were reported in younger people ages 18 to 59, according to the FDA, although most age groups reported similar nausea rates.

FDA staff found that most people who received the vaccine were able to shake off the side effects within days of their shot.

While the rate of unexpected side effects was similar between the vaccine and placebo groups, there was a slight imbalance between some reactions in the vaccine group and those who received a placebo. The vaccine group reported 15 cases of “embolic and thrombotic events” or blood clots in 14 recipients, compared with 10 in the placebo group.

There were also six cases of tinnitus, a ringing or buzzing in at least one ear, among vaccine recipients compared to none in the placebo group, the FDA found.

However, the agency said current data “is insufficient to establish a causal link between these events and the vaccine”.

The report found a “balanced” number of cases of Bell Paralysis, a condition in which half of your face falls off. The FDA previously announced that the condition would be monitored in recipients of other vaccines and noted that this isn’t necessarily a side effect, but it’s worth looking out for.

The FDA said there were no reports of anaphylaxis – a serious and life-threatening allergic reaction that rarely occurs after vaccination – immediately after receiving the J&J shot.

Some cases of anaphylaxis have been reported in people who received either Pfizer’s or Moderna’s shot, although researchers say they occurred in the range of cases reported for the influenza vaccine, according to a report by the Centers for Control and Prevention released Friday from diseases.

J&J first submitted its Covid vaccine data to the FDA on February 4th. While the level of vaccination protection varied by region, the company said it had prevented 100% of hospital admissions and deaths.

– CNBC’s Berkeley Lovelace Jr. contributed to this report.