Effectiveness and safety of Moderna COVID-19 vaccine confirmed, path cleared for expected authorization this week

Vaccine maker Moderna is poised to win authorization for its COVID-19 vaccine 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, the vaccine is likely to be authorized this week by the FDA commissioner.

An independent advisory committee to the U.S. Centers for Disease Control and Prevention will review the data this weekend and will vote on whether to add the vaccine to the nation's vaccine schedule for adults.

Then, as with Pfizer-BioNTech's vaccine, it will be distributed across the country, probably starting Monday.

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 required for full approval. Both are likely to apply for full approval once they collect 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, and 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 temporary side effects in most people a day or two after the shot, 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, all passed within a few days.

Though 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. 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. 

The vaccine trials looked only at whether the shots prevented symptomatic disease, not transmission. They can't rule out the possibility that people can still catch COVID-19 and become contagious even after vaccination. More studies should answer that question next year. Experts recommend that people who are vaccinated continue to wear masks and maintain social distance. 

The studies did not include large numbers of pregnant or nursing women, so it's not clear whether the vaccine is safe for them. Experts said last week that although the benefits of the Pfizer-BioNTech vaccine are likely to outweigh the risks, particularly compared with catching COVID-19, a pregnant woman should make an individual decision in consultation with her doctor. 

Not enough trial participants were immunocompromised with diseases such as HIV to draw conclusions about their safety in receiving the vaccine.

Children were also not included.

All three groups will be the subject of future trials.

Research will also be needed to confirm whether the vaccine causes enhanced disease, an unlikely but possible result of vaccination. For instance, some people who caught dengue fever after vaccination became sicker than those who did not get the vaccine. 

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

Seven vaccine recipients and four who got the placebo ran fevers that lasted more than a week.

Fifteen of the vaccine recipients reported very high fevers, over 104 degrees, most after the second dose. One person in the vaccine group reported severe fatigue and one severe joint pain. None of the severe reactions was in someone over 65.

Similar to the Pfizer-BioNTech trial, three people who received the Moderna vaccine developed Bell's palsy several weeks after vaccination, compared with one person in the placebo 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 coincidentally. 

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

In any group of 30,000 people tracked for months, some will have medical issues. FDA investigators said most were not linked to the vaccine, because the numbers were small and generally distributed between the placebo and vaccine groups.

Other health problems are likely to crop up as more people are vaccinated; regulators will try to figure out whether they are related to the vaccine or coincidental.

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. About a quarter of participants are health care workers eligible to receive the earliest doses of the vaccine, as soon as next week. They will be "unblinded" to learn whether they received the active vaccine, and to receive it if they did not already. The rest will probably be unblinded as they become eligible to receive vaccine.

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, will decide what further studies to require as the vaccine is distributed.

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 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 six 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 U.S. population.

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, and 25% were over 65 years old, which also put them at higher risk.

Slightly more than 2% of participants tested positive for COVID-19 when they joined the trial. Researchers followed participants as they got both doses of the vaccine, then began counting cases of COVID-19 among both vaccine and placebo recipients two weeks after their second dose until Nov. 21, the trial cutoff date.

Almost 200 trial participants developed symptomatic COVID-19 in that time frame, 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 was in the vaccinated group.

The data did not break down the final infected participants by subgroup, but an earlier analysis found that only one of those in the vaccinated group who developed COVID-19 symptoms had a high body-mass ratio, putting that person at risk for severe disease. The others in the vaccinated group were white, under 65 and had no conditions that would put them at risk for severe COVID-19.

A small number of participants caught COVID-19 between their first and second dose. The vaccine appeared to be 80% protective in that group, suggesting that one dose is at least partially protective. Because they received a second dose so quickly, it's not clear how long that protection would last. Six of those 46 people had severe COVID-19, two in the vaccine group and four in the placebo group.

Contact Karen Weintraub at kweintraub@usatoday.com

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