9 Things to Know About COVID-19 Vaccine Safety & Development

While the beginning distribution phases of the COVID-19 vaccines are spreading hope and optimism for some, questions around everything from speed to market to efficacy and side effects are still swirling in the minds of many. Is it safe? Should I get it? If so, when can I get it?

With expert guidance from Dr. Patricia Toro, MD, MPH, associate medical director of Harvard Pilgrim Health Care and infectious disease specialist, as well as trusted medical sources, we’ve sought to help answer these pressing questions and ease concern.

Here’s what you need to know right now about the COVID-19 vaccine development, safety and efficacy:

1. What is the COVID-19 vaccine?

By definition, vaccines are substances that help to protect against and prevent certain illnesses. In more recent years, a new type of vaccine called a messenger RNA (mRNA) vaccine has been developed and implemented for earlier coronaviruses like SARS and MERS. Instead of putting weakened or activated germs in the body like traditional vaccines, the mRNA vaccine teaches cells how to make a protective protein. Should the real virus enter the body, that new protein triggers an immune response that produces antibodies and prevents us from getting sick.

Having an existing blueprint from previous mRNA vaccines enabled vaccine manufacturers to develop a new variation for COVID-19 with greater efficiency and effectiveness. Dr. Toro notes that it was also one of several reasons they were able to do so on a significantly expedited timeline, in “10 months versus 10 to 15 years.”

2. How does it work?

mRNA vaccines help create a protein in the body. More specifically, the COVID-19 vaccine instructs our cells to create the “spike protein”–a protein found on the surface of the virus that causes COVID-19. Here’s a breakdown of how the vaccine works in our bodies:

3. How was it developed and authorized?

All vaccines are required to go through extensive testing before they’re approved or authorized for emergency use by the U.S. Food and Drug Administration (FDA) and introduced to the public. With prioritized funding and resources, and trials running in parallel, the COVID-19 vaccine went through the same clinical development process as all other new vaccines, just in a much shorter time frame. The World Health Organization breaks down new vaccine development as follows:

The vaccine is administered to a small number of volunteers to test for 1) safety, 2) efficacy (does it generate an immune response?) and 3) the appropriate dosage. In this phase, vaccines are typically tested on young, healthy, adult volunteers.



Then the vaccine is given to several hundred more volunteers to further determine its safety and ability to generate an immune response. Participants in this phase generally have the same characteristics (such as age and sex) as the intended audience of the vaccine, and there are usually multiple trials to evaluate different age groups and formulations of the vaccine. At this stage, a control group (a group that gets a placebo instead of the real vaccine) is added to determine if changes in the vaccinated group are truly caused by the vaccine or occurred by chance.



Next, the vaccine is administered to thousands more volunteers and compared to a control group to determine effectiveness and safety in a larger number of volunteers. Moderna enrolled about 30,000 volunteers while Pfizer enrolled a little more than 43,000, numbers Dr. Toro notes are typical for a Phase 3 trial. These trials are often conducted across several countries and sites within a country to confirm that the vaccine performance findings apply to different populations. Every Phase 3 study is reviewed by the Data Safety Monitoring Board, so that the clinical trial is stopped should the participants be harmed by the vaccine. For both of these vaccines, the Phase 3 study was completed and safety was maintained to the end.

4. Should I get vaccinated?

The CDC reports that current data shows the vaccine is highly effective (> 94%) at preventing COVID-19 illness. Getting vaccinated can help protect both you and your loved ones, especially those at high-risk, from getting sick. If you have questions, you can discuss them with your health care provider.

After a vaccine has completed all three clinical development phases, typically the company that has developed the vaccine will submit a Biologics License Application (BLA) to the FDA seeking approval to market and distribute in the U.S.

Recognizing the COVID-19 pandemic as a public health emergency, however, vaccine manufacturers instead submitted an Emergency Use Authorization (EUA) request to the FDA, which enables the vaccine to be distributed to the public prior to receiving FDA approval. In order to authorize an EUA, the FDA must first rigorously evaluate all the data available and then determine that the potential benefits outweigh the potential risks. After an EUA has been issued, as it has with the COVID-19 vaccines, both the vaccine manufacturer and the FDA continue to closely monitor the vaccines as more data becomes available.

5. When can I get vaccinated?

While the COVID-19 vaccine is currently available in all states, availability is limited and will be phased out to priority groups determined by each individual state. For the general public, Massachusetts is expecting to start vaccinations as early as April; however other states are anticipating this will be closer to June and beyond. Use the following resources to stay in the know on the coronavirus vaccine timeline in your state:

6. What can I expect when I get vaccinated?

There are currently two vaccines authorized for emergency use in the U.S.–Moderna and Pfizer–both with high efficacy rates. Regardless of the type you receive, two shots will need to be taken a few weeks apart for maximum protection. In the next couple of months, however, vaccines from additional manufacturers are also expected to be approved under EUA and not all require two doses.

Once you receive the vaccine, the CDC has developed a smartphone app called v-safe that you can download to help monitor your health and remind you when you’re due for your second dose.

7. Is the vaccine safe? Are there side effects?  

These vaccines are safe. Just like with any vaccine, COVID-19 vaccine side effects can occur as your body starts to build protection and can include swelling or pain at the site of the shot, fevers, chills, tiredness or headaches. These symptoms may last one to two days and are generally mild. This shows that the vaccine is working in your body.

After you’ve been vaccinated, you can use the CDC’s v-safe app to get personalized health check-ins and report any side effects. If needed, a CDC professional will follow up to get additional information.

8. What about new strains or “variants?” Will this vaccine protect me against them?

Yes. Because these new mutations are genetically similar to the old strain, displaying the spike protein, they are still effective. Both Moderna and Pfizer have tested their vaccines against these variants and found them to be effective.

Dr. Toro further explains that “if the variants mutate more and the vaccines become ineffective, then these mRNA vaccines can be ‘re-tooled’ within 6-8 weeks to work specifically against the variants.”

9. How long will the vaccine last?

Since the vaccine is so new, it’s unclear how long it will last until more data becomes available.

While there’s a lot we now know and can prepare for with the COVID-19 vaccine, there is still so much that’s consistently changing. Over the next few months, remember to stay aware of updates from your individual state, as well as the CDC for new developments and changes in availability. And remember that we are still in a pandemic, so for the protection of yourself and others, wear a mask and keep up the social distancing.

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