CDC Panel: No Safety Surprises for COVID-19 Vaccines

Brenda Goodman

January 27, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Jan. 27, 2021 — The United States is nearly 6 weeks into its historic campaign to vaccinate Americans against the virus that causes COVID-19, and so far, the two vaccines in use look remarkably low-risk, according to new data presented today at a meeting of vaccine experts that advise the Centers for Disease Control and Prevention (CDC).

With 23.5 million doses of the Pfizer and Moderna vaccines now given, there have been very few serious side effects. In addition, deaths reported after people got the vaccine do not seem to be related to it.

The most common symptoms reported after vaccination were pain where people got the shot, fatigue, headache, and muscle soreness. These were more common after the second dose. In addition, about 1 in 4 people reported fever and chills after the second shot.

"On the whole, I thought it was very reassuring," said William Schaffner, MD, an infectious disease expert with Vanderbilt University School of Medicine in Nashville who listened to the presentations.

The CDC is collecting safety information through multiple channels. These include a new smartphone-based app called V-Safe, which collects daily information from people who've been vaccinated; the federal Vaccine Adverse Event Reporting System, or VAERS, which accepts reports from anyone; and the Vaccine Safety Datalink, which is a collaboration between the CDC and nine major hospital systems. There's also CISA, the Clinical Immunization Safety Assessment Project, a collaboration between the CDC and vaccine safety experts.

After surveying these systems, experts heading the safety committee for the CDC's Advisory Committee on Immunization Practices say there have been few serious side effects reported.

Very rarely, anaphylactic reactionss have occurred after vaccination. There have been 50 of these cases reported after the Pfizer vaccine and 21 cases reported after the Moderna vaccine to date. Nearly all of them — 94% of the anaphylaxis cases after Pfizer vaccines and 100% of those after Moderna's vaccine — have been in women, though it's not clear why.

That translates to a rate of about five cases of anaphylaxis for every million doses of the Pfizer vaccine and about three for every million doses of the Moderna vaccine. Most of these occur within 15 minutes after getting a vaccine dose, with one reported as long as 20 hours after the shot.

The CDC suspects these may be related to an ingredient called polyethylene glycol, or PEG. PEG is a part of the particles that slip the vaccines' mRNA into cells with instructions to make the spike protein of the virus. Cells then express these spikes on their surfaces so the immune system can learn to recognize them and make defenses against them. PEG is a common ingredient in many drugs and occasionally triggers anaphylaxis.

Reported Deaths Seem Unrelated to Vaccines

Through January 18, 196 people have died after getting a vaccine.

Most of these deaths — 129 — were in patients in long term care facilities. These deaths are still being investigated, but when they were compared with the number of deaths that might be expected over the same period due to natural causes, they seemed to be coincidental and not caused by the vaccine, said Tom Shimabukuro, MD, deputy director of the Immunization Safety Office at the CDC, who studied the data.

In fact, death rates were lower among vaccinated nursing home residents, compared to those who had not been vaccinated.

"These findings suggest that short-term mortality rates appear unrelated to vaccination for COVID-19," Shimabukuro said.

This also appeared to be true for younger adults who died after their shots.

There were 28 people under age 65 who died after being vaccinated. Most of these deaths were heart-related, according to autopsy reports. When investigators compared the number of sudden cardiac deaths expected to occur in this population naturally, they found people who were vaccinated had a lower rate than would have been expected without vaccination. This suggests that these deaths were also unrelated to the vaccine.

More Vaccines on the Horizon

The panel also heard an update from drug company AstraZeneca on its vaccine. It's being used in 18 countries but has not yet been authorized in the US.

That vaccine is currently in phase III of its US clinical trials, and more than 26,000 people who have volunteered to get the shot had received their second dose as of January 21, the company said.

The FDA requires at least 2 months of follow-up before it will evaluate a vaccine for an emergency use authorization, which means the company would be ready to submit by the end of March, with a possible approval by April.

The AstraZeneca vaccine uses a more traditional method to create immunity, slipping a key part of the virus that causes COVID-19 into the shell of an adenovirus that normally infects monkeys. When the immune system sees the virus, it generates protective defenses against it.

The two-dose vaccine can be stored in a regular refrigerator for up to 6 months, which makes it easier to handle than the mRNA vaccines, which require much colder storage. Another advantage appears to be that it's less likely to trigger severe allergic reactions. So far, there have been no cases of anaphylaxis reported after this shot.

In total, four serious side effects have been reported with the AstraZeneca vaccine, including two cases of transverse myelitis, a serious condition that causes swelling of the spinal cord, leading to pain, muscle weakness, and paralysis. One of these was in the group that got the placebo. The reports paused the trial, but it was allowed to continue after a safety review.

This vaccine also appears to be less effective than the mRNA shots. Data presented to the panel show it appears to cut the risk of developing a COVID infection that has symptoms by 62%. That's over the 50% threshold the FDA set for approval but less than seen with the mRNA vaccines, which are more than 90% effective at preventing infections.

"Is the average person going to want to take the AstraZeneca shot? What role is this going to play in our vaccination program?" Schaffner said.

Johnson & Johnson will have enough data from its clinical trials to submit it to the FDA within the next week, the company said in a call with shareholders on Tuesday. So far, its one-dose shots looks to be about as effective as both the Pfizer and Moderna vaccines.

"It could be that we wind up with four vaccines: Three that can run very fast, and one that's not so fast," Schaffner said.

Sources:

William Schaffner, MD, professor of preventive medicine, Department of Health Policy, Vanderbilt University School of Medicine, Nashville.

CDC: Advisory Committee on Immunization Practices meeting, Jan. 27, 2021.

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