COVID-19 vaccines: Answering the big questions



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The past nine months have shown me that the things I treasure most in life are some of the simplest. I miss being able to hug my parents. I miss sitting my niece on my lap to share my dessert so she’ll sit still for just a little longer during family dinners. I miss doing home science experiments with my nephew. I miss traveling. I miss sitting around a campfire with friends. I miss walking my dogs or going for a run without having to wear a mask.

As an epidemiologist and vaccine advocate, I know that safe, effective vaccines are our best chance at making it through this pandemic and returning to a more normal life. Like many of you, I’ve been following COVID-19 vaccine development closely.

There’s a lot of information circulating about COVID-19 vaccines and it can be hard to know what to believe and which sources of information can be trusted. I’ve spent many hours reading and making sense of the results from clinical trials and information provided to regulatory agencies by the vaccine manufacturers. Based on the many conversations I’ve had in my personal life about COVID-19 vaccines, I know that many of you are wondering about vaccine safety, and wanted to share some of the questions I’ve encountered.

Which vaccines are available?

There are currently two vaccines whose manufacturers have requested review by the Food and Drug Administration (FDA) in the U.S. for emergency use authorization. The first, produced by Pfizer and BioNTech, was approved for use in the U.K. and Canada earlier this month, and was authorized for use in the U.S. just a few days ago. The second, produced by Moderna, is scheduled for FDA review on Dec. 17. Both vaccines use messenger RNA (mRNA) packaged inside lipid nanoparticles to teach the immune system how to generate antibodies against one of the proteins on the surface of SARS-CoV-2, the virus that causes COVID-19, so that the virus can’t enter your cells. This technology has been used before to develop vaccines against SARS, which is how we were able to develop and move these vaccine candidates into clinical trials so quickly.

Do vaccines work?

Efficacy of two doses of the Pfizer and BioNTech vaccine is 95%; efficacy of the Moderna product is 94.5%. This is phenomenal. Effectiveness (how well the vaccine works in the real world) will undoubtedly be lower (it always is), but greater than 90% efficacy means that we have every reason to think the vaccine will work well in the general population.

So, what does this actually mean? In clinical trials, the vaccine prevented approximately 95% of COVID-19 disease in people who were vaccinated, and only approximately 5% of vaccinated people developed COVID-19 disease. The clinical trials included older adults, those with chronic medical conditions and Black and Hispanic/Latino individuals; all groups who’ve been disproportionately impacted by COVID-19. It’s encouraging that the vaccine works well in groups who’ve felt the burden of COVID-19 the most.

How long will vaccines work?

We honestly don’t know. Moderna released information earlier this month from a subset of participants that demonstrated high antibody levels (higher than seen in a comparison group of individuals who had recently had COVID-19) four months after their first dose of vaccine. As clinical trials progress, we’ll know more about how long immunity lasts and if booster doses will be necessary.

Are vaccines safe?

From preliminary data, we know mild side effects are common. We know that if you’re vaccinated, you should expect to experience some side effects, particularly after the second dose. In the Pfizer and BioNTech trial, the overwhelming majority of these were mild. Of all vaccine recipients, the most frequently reported side effects included pain at the injection site (in 84%), fatigue (in 63%), headache (in 55%), muscle pain (in 38%), chills (in 32%), joint pain (in 24%), and fever (in 14%). 

These may seem scary, but they’re all common side effects that may occur after any vaccine. It’s important to note that none of these side effects were severe enough to require medical attention and most had minimal impact on participants’ daily activities. Although uncomfortable, these side effects are a sign that your immune system is responding to the vaccine and is learning to recognize the virus for the future.

The short-term safety of these vaccines is clear.

But, what about rare side effects and long-term risks after vaccination?

Animal studies have shown that the short-term side effects I mentioned above are due to the lipid nanoparticle component of the vaccine, and not the mRNA itself, which is reassuring. But, it’s impossible to answer this question definitively until we have more data. It’s possible there could be a rare side effect that affects 1 in a million recipients, for example, but if this occurred, it would be so rare that it wouldn’t be detected until millions of doses had been administered. We’d never accumulate this information from clinical trials. Vaccine manufacturers and public health agencies like the Centers for Disease Control and Prevention (CDC) conduct long-term safety studies after vaccine approval by combining information about doses given globally to assess rare risks.

Putting it all together

So, how do I make this decision?

COVID-19 is certainly nothing to mess around with! When I think about my own health, I worry about the relatively high percentage of individuals who recover from COVID-19, but develop long-term side effects such as chronic exhaustion, shortness of breath, neurologic impairment and headaches. This phenomenon, called COVID long-hauling, has been reported in up to 10% of individuals with COVID-19, including those with mild disease that did not require hospitalization, and is severe enough to prevent those affected from returning to normal activities months after infection. Beyond this, we know children with COVID-19 may develop an inflammatory syndrome (multi-system inflammatory syndrome in children; MIS-C) that is life-threatening and cases are now being reported in adults. If this isn’t bad enough, almost 300,000 Americans have died and we know many thousands more will lose their lives before vaccine is widely available and the pandemic runs its course.

Even though I’m young and healthy, I’ve learned through this experience that we’re all in this together and that, collectively, our actions impact the lives of those around us. My parents are older, and like so many their age, have chronic medical conditions that place them at high risk for severe disease. When I take all this into consideration, the likelihood of harm to me and my loved ones or long-term risk to my own health is far greater from COVID-19 disease than it is from any rare side effect that might be experienced after receiving either the Pfizer and BioNTech or Moderna COVID-19 vaccines.

I’m confident in the technology used to develop these vaccines, the possible mild side effects, and the scientific community’s ability to monitor for long-term, rare side effects. I am eager to roll up my sleeve to receive this life-saving vaccine as soon as I’m offered a dose. I will have done my part to help return us to a more normal life.