Tips to Live By

Here's What We Know About COVID-19 Vaccine Safety

Dec. 10, 2020 - Katie McCallum

In December, 2020, the first COVID-19 vaccines, the Pfizer and Moderna mRNA vaccines, were granted Emergency Use Authorization (EUA) by the FDA — a welcome milestone during a pandemic that has felt overwhelming and insurmountable at times.

More recently, Johnson & Johnson's viral vector COVID-19 vaccine received EUA.

Each of these vaccines provides strong protection against COVID-19 — reducing severe illness, hospitalization and death — and have similar types and rates of side effects.

But, like any new drug or vaccine, you may still be worried about whether the vaccine is safe or perhaps about getting vaccinated "too soon" — before we might know all of the possible adverse effects.

"What I would say to people who are fearful of receiving the COVID-19 vaccine is that, before granting EUA, the FDA thoroughly reviews the safety and efficacy of each vaccine," says Dr. H. Dirk Sostman, president of the Academic Institute at Houston Methodist. "A vaccine is our best tool for gaining control on this pandemic, and I myself plan to get vaccinated as soon as it's made available to me."

Here's what we know when it comes to the safety of COVID-19 vaccines:

FDA-approved vaccines have undergone thorough testing and rigorous external review

Any time a new drug or vaccine is developed, rigorous safety testing is performed. This testing is then scrutinized by independent scientific panels.

"Before a vaccine can be made available to the public, it has to undergo clinical trial testing — a multistep process that tests for both safety and effectiveness in three separate phases. If during testing a vaccine is deemed unsafe, the trial is halted immediately," explains Dr. Sostman.

In fact, while all three phases of a clinical trial check for safety, the first two phases are almost completely devoted to it.

"In the first phase of a clinical trial, the vaccine is given to a small group of people to determine whether it's safe. The second phase incorporates more people to further check for safety and to monitor for side effects," says Dr. Sostman. "All the while, an external review board, called the Data Safety Monitoring Board (DSMB), monitors trial data and results. This is a completely independent panel of experts who are often kept confidential, and this panel determines whether a trial should continue or not as trial data rolls in."

After a trial is complete, the results are further reviewed by three more panels of experts.

The complete results of the trial are reviewed by the FDA staff, the FDA’s the Vaccines and Related Biological Products Advisory Committee (VRBPAC), along with the CDC staff  and the CDC’s Advisory Committee on Immunization Practices (ACIP). The VRBPAC and ACIP committees are independent. This means that both committees are comprised of a panel of scientists and public health experts who have no political appointments and aren't affiliated with any government-regulated agencies.
Thus, these COVID-19 vaccines have gone through preclinical testing, three phases of clinical trials and external review by two independent panels of experts and two civil service scientific reviews.

EUA doesn't mean a vaccine is less safe — here's what it does mean

The term "Emergency Use Authorization (EUA)" may sound like the COVID-19 vaccine is being distributed before it's ready for prime time, but this is a misconception.

EUA simply means that the vaccine was prioritized to the top of the FDA's queue of new therapies and devices to review. The FDA generally uses the EUA during a public health crisis, when there's an immediate need for a vaccine or new treatment. For instance, early in the pandemic, convalescent plasma therapy was approved by the FDA via the EUA process.

"If a vaccine has received EUA, it means the FDA has deemed it safe and effective. The same Phase 3 clinical trials and the same scientific review panels previously mentioned will have carefully assessed the trial data and results, and with the same level of scrutiny as usual," says Dr. Sostman.

Vaccine testing and safety aren't sacrificed for speed

It typically takes years to develop a vaccine. In the case of the COVID-19 vaccine, however, the first vaccine has now been granted EUA by the FDA — less than a year after the pandemic began.

"While COVID-19 vaccine development has moved along much more rapidly than it has for previous vaccines, the FDA has stated that the level of safety testing remains unchanged," says Dr. Sostman. "Rather, the primary reasons for the quickness with which these COVID-19 vaccines are coming to market has more to do with the types of vaccine technology being leveraged and the amount of federal financial backing vaccine manufacturers have been given."

The main reasons that COVID-19 vaccine development has progressed so rapidly, without sacrificing safety, are:

  • Newer vaccine technology is being used
  • There is unprecedented financial support
  • Researchers were able to leverage previous coronavirus research
  • Hundreds of vaccine candidates are being developed and tested simultaneously

"In particular, the fact that researchers could leverage previous research meant that vaccine candidates were entering clinical trials around the same time our country was seeing its first wave of COVID-19 cases. This is really unprecedented," adds Dr. Sostman. "Add to that the fact that vaccine manufacturers faced significantly less financial risk, as the government backed many of the most promising vaccines."

Given all of this, faster vaccine development became possible — entirely borne out of a need to bring a safe, effective vaccine to the public quickly.

"It's true that we don't have years of long-term follow up for the vaccines now being reviewed. However, the months of follow up that we do have cover the period when issues with vaccines are normally discovered," adds Dr. Sostman.

Safety is of paramount importance at our hospitals

As the No. 1 hospital in Texas for patient care and safety, you can be sure that Houston Methodist isn't taking COVID-19 vaccine safety lightly. Everything we do at Houston Methodist puts our patients, and their safety, first.

Each vaccine is made slightly differently, and you should not take any vaccine that contains an ingredient you are allergic to:


This article was updated on March, 10 2021 to reflect the current state of the COVID-19 vaccine landscape.

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