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Your Questions About COVID-19 Vaccines, Answered

Are coronavirus vaccines safe? What's in them? Is one option better than another? Will a vaccine make me immune? How long will they remain effective? Has anyone died after getting the vaccine?

By Nathaniel Scharping
Mar 26, 2021 4:48 PMMar 21, 2023 8:19 PM
senior residents in los angeles waiting for their covid-19 vaccine - shutterstock
(Credit: Ringo Chiu/Shutterstock)


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The first vaccines against COVID-19 began to be injected into people’s arms in December of 2020, less than a year after the pandemic began. It’s a staggering, unprecedented achievement that will undoubtedly save millions of lives. Today we have not one, but three, effective vaccines against COVID-19.

Understandably, questions about what’s in the vaccines, what side effects exist, and more abound. While the Centers for Disease Control and Prevention (CDC) is your best resource for information about the vaccines, here’s a quick primer on the various options and how they work.

What’s in the COVID-19 vaccine?

Traditional vaccines give our bodies an actual virus (or a piece of it), often in a weakened or dead form. This lets our bodies learn to recognize this particular threat and produce specialized defenses against it. But mRNA vaccines, like those made by Pfizer-BioNTech and Moderna are different. Instead of giving our bodies a piece of a virus, mRNA vaccines teach us to make it ourselves. 

This is how it works: The vaccines contain a piece of RNA, which is the genetic code our cells use to make proteins. In this case, the RNA contains the specific genetic blueprints for the SARS-CoV-2 spike protein, which the virus uses to attach to our cells.

Once given the RNA, our cells churn out replica spike proteins (which are harmless to us), and that allows our immune systems to create special antibodies for the virus that causes COVID-19. That way, if we’re infected by the actual virus, our bodies know what to do. The Johnson & Johnson vaccine also delivers genetic instructions for making the spike protein (though as DNA, not RNA), but it uses a more traditional viral vector to deliver them. 

How long will the COVID-19 vaccine last?

There’s not enough data yet to say how long immunity to COVID-19 from vaccines will last. Remember, large-scale vaccinations only began at the end of 2020. It will take months before we start to see reliable data on how long people remain protected for.

For a rough idea, we can look to data on how long people who actually got infected with COVID-19 remain immune for. Though it’s not a perfect proxy, multiple studies are showing that recovered COVID-19 patients still show evidence of adaptive immunity to the virus after six months, and perhaps even longer. As with the vaccines, it’s still too early for us to have really good data on this.

But new variants of the disease could add a level of uncertainty to these figures. Mutated versions of COVID-19, as we’ve seen pop up in South Africa and the U.K., could pose a threat even to people who have been vaccinated or have already had the disease. Preliminary data is showing that existing COVID-19 vaccines offer some protection against new variants of the disease, but at lower levels than before.

Has anyone died from the COVID-19 vaccine? Are there side effects?

There’s no evidence that anyone has died as a result of receiving a COVID-19 vaccine in the U.S. Allergic reactions can happen rarely, and there are a number of mild, common side effects that can follow a vaccination. These include soreness at the injection site, tiredness, headache, muscle pains, fever and chills, according to the CDC.

More rarely, people may have an allergic reaction to specific components of the vaccine. These can be more serious, but reports of this happening are rare, and no one has died. These allergic reactions are the reason healthcare providers ask vaccine recipients to stick around for up to half an hour after getting the shot.

While you may see reports from the CDC that mention people dying after getting the COVID-19 vaccine, there’s an important distinction to be made. That data captures people that died for many unrelated reasons, and includes things like cancer and old age. There’s no evidence that the COVID-19 vaccine played a role in any of those deaths. 

Which vaccine is better?

The three vaccines currently approved for use in the U.S. differ slightly in their rates of effectiveness. But all of them confer a significant level of protection against COVID-19.

Trials of the Pfizer-BioNTech vaccine showed it to be up to 95 percent effective at protecting people against symptomatic disease, and the Moderna vaccine is 94 percent effective. Meanwhile, the Johnson & Johnson vaccine, approved more recently, is 66 percent effective at protecting against COVID-19, but 85 percent effective against severe disease. Those statistics may vary somewhat as the vaccine rollout continues and more people get the shots.

Vaccine effectiveness numbers can be confusing. For example, a 95 percent effectiveness rate does not mean that five of every 100 people who get vaccinated contract COVID-19. Instead, it means that five percent of people exposed to the virus experience symptoms. If just one percent of vaccinated people are actually exposed to the virus, that works out to just .05 percent of the vaccinated population contracting the disease.

Side effects from these three vaccines all appear to be roughly similar, and more serious adverse events occur only very rarely.

While the lower effectiveness rate of the Johnson & Johnson vaccine might seem to make it a poorer option, there are other factors to consider. That vaccine can be delivered in just one shot, compared to two for Moderna and Pfizer-BioNTech. The Johnson & Johnson vaccine also does not need to kept as cold as the other two. It can be stored using commercial refrigeration technology, as opposed to the deep freeze necessary to keep the two-shot vaccines viable.

That means the Johnson & Johnson vaccine can be delivered more quickly to more people with less logistical hassle. Vaccinating people quickly can be as important as giving them strong protections from the disease, so it’s difficult to say which vaccine is truly the best. Ultimately, any of these three will help protect you from COVID-19. 

Does a vaccine mean you're immune?

Getting vaccinated against COVID-19 does not mean you’re completely immune to the disease. You can still get infected with the SARS-CoV-2 virus, and some people may still experience symptoms of the disease. But symptomatic cases of COVID-19 are far lower among people that get vaccinated — just 5 percent of people that get the Pfizer-BioNTech vaccine and are exposed to the coronavirus experience symptoms. 

Furthermore all three vaccines approved in the U.S. appear to be very effective at preventing severe disease in COVID-19 patients.

But even if you’re vaccinated you could still potentially pass the virus to those around you. That’s because, while the vaccine does help your body recognize and fight off SARS-CoV-2, it doesn’t prevent the virus from entering your body. That means the coronavirus can still infect your body’s cells and replicate, and potentially be passed to someone else.

For that reason, the CDC still recommends that people who have been vaccinated continue to wear masks and socially distance in public and around people from multiple households that haven’t received the vaccine yet.

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