Vaccine maker Moderna appears poised to win authorization for its COVID-19 vaccine just days after Pfizer-BioNTech did the same.

Data released Tuesday by the U.S. Food and Drug Administration, confirmed that Moderna’s vaccine appeared safe and highly effective in a study of more than 30,000 volunteers.

Unlike Pfizer-BioNTech’s vaccine, Moderna’s will be given only to adults. The company has begun testing in teenagers, but has not accumulated enough data to include in its authorization request to the FDA.

An independent advisory committee to the FDA will review the data in an all-day meeting Thursday. If the Vaccines and Related Biological Products Advisory Committee decides that the vaccine’s benefits outweigh its risks, then the vaccine is expected to be authorized later in the week by the FDA commissioner.

An independent advisory committee to the U.S. Centers for Disease Control and Prevention will review the data on Friday, and if the FDA has signed off, will vote on Saturday whether to add the vaccine to the nation’s vaccine schedule for adults.

Then, as with Pfizer-BioNTech’s vaccine, it will begin to be distributed across the country, likely on Monday.

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The FDA will “authorize” the vaccine, but stop short of a full approval. The companies have met requirements for so-called emergency use authorization, but do not have the longer-term data that will be required for full approval. Both are expected to apply for full approval at some point, based on this data.

There are no major differences in safety or effectiveness identified between these first two vaccines, although the two Moderna vaccine doses should be given 28 days apart, while Pfizer-BioNTech’s second shot should be given after 21 days. 

Both rely on a technology called mRNA to make a bit of protein from the virus that causes COVID-19, training the immune system to attack it.

Moderna’s vaccine, called mRNA-1273, was shown to be 94% effective overall, with no major differences by age, race, gender, previous infection with COVID-19 or other medical problems.

The vaccine will cause side effects in most people, the data confirms. 

More than 90% of recipients had pain around the injection site, nearly 70% suffered fatigue, 63% had headache, 60% muscle pain, 45% joint pain and 43% chills. Those side effects, which were worse after the second shot and more common in those under 65, were enough to be noticeable, but all passed within a few days.

While side effects are uncomfortable, they are signs that the immune system is responding to the vaccine, and are not cause for concern, said Dr. Paul Offit, who directs the vaccine education center at Children’s Hospital of Philadelphia.

The vaccine cannot cause COVID-19, because it contains only a harmless fraction of the virus. A although the symptoms of the disease and the side effects of the vaccine can be similar, the vaccine won’t cause breathing problems or coughing. 

No one in the trial had a severe allergic or hypersensitivity reaction to the Moderna shot, although several people in the U.K. have had allergic reactions to the Pfizer-BioNTech vaccine.

Similar to the Pfizer-BioNTech trial, three people who received the Moderna vaccine did develop Bell’s palsy, compared to one person in the vaccine group. Bell’s palsy, a temporary paralysis of half the face, occurs regularly in the general population, and there were not enough cases to determine whether they were caused by the vaccine or happened coincidently. 

Bell’s palsy is one of the conditions the government will continue to track as the vaccines are rolled out to the general public.

No one died in the vaccinated group, compared to one death among participants who received a placebo.

Although people over 65 had fewer reactions to the vaccine, as is to be expected because their immune systems are less robust, there were no other differences in side effects reported by age, gender, ethnicity and race, among people with or without medical problems or those with or without prior infection with the virus that causes COVID-19. 

The company will continue to follow clinical trial participants after authorization, although some participants will be “unblinded” to learn whether they received the active vaccine, and to receive it if they did not already.

As well as deciding whether the vaccine’s benefits outweigh its risks, the committee, whose meeting is expected to run from 9 a.m. to 6 p.m.Thursday and will be webcast live, also will decide what further studies to require as the vaccine is distributed across the country.

The Moderna vaccine does not contain preservatives, but in addition to the active mRNA ingredient, contains: lipids (SM-102, 1,2-dimyristoyl-rac-glycero3-methoxypolyethylene glycol-2000 [PEG2000-DMG], cholesterol, and 1,2-distearoyl-snglycero-3-phosphocholine [DSPC]), tromethamine, tromethamine hydrochloride, acetic acid, sodium acetate, and sucrose.

People who are allergic to any of these ingredients are advised not to take the vaccine.

Although it is very similar to the Pfizer-BioNTech vaccine, the Moderna vaccine does not need to be kept as cold.

Moderna’s vaccine comes in a multi-dose vial with 10 doses. Vials can be stored in a refrigerator for up to 30 days before using; after the first dose has been withdrawn, the vial should be used or discarded within 6 hours.

In terms of demographics, nearly 10% of the trial participants were Black, 4% were Asian, and 20% described themselves as Hispanic or Latino, roughly reflecting the population of the United States.

About 22% of participants had one or more medical conditions that put them at extra risk for severe COVID-19, such as diabetes, heart disease or lung disease, while 25% were over 65 years old, which also put them at higher risk.

Just over 2% of participants tested positive for COVID-19 when they joined the trial.

The trial followed participants as they got both doses of the vaccine and then began counting cases of COVID-19 among both vaccine and placebo recipients two weeks after their second dose until the Nov. 21 trial cutoff date.

Just under 200 trial participants developed symptomatic COVID-19 in that timeframe, only 11 of whom had received the active vaccine. Because the infection rate was so much higher in the placebo group, statistical analysis determined that the vaccine was 94% effective overall.

Four of the people who fell ill in the vaccinated group were over 65 years old, putting the effectiveness rate in that age group at 86%, according to the company’s data. None of the 30 cases of severe COVID-19 were in the vaccinated group.