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Get answers to some of the most common questions people ask about the COVID-19 vaccine, including the science behind the vaccine, availability, eligibility and side effects.

About the vaccine science

Messenger RNA (mRNA) is a technology used in the Pfizer-BioNTech and Moderna vaccines that helps the body learn how to protect itself against COVID-19.

No, it does not manipulate your DNA. mRNA does not get anywhere near the cellular DNA. Instead, mRNA gives instructions to the body’s cells. In the COVID vaccine, those instructions tell the body’s cells how to make one part of the virus that causes COVID-19. When your body produces this protein, the immune system will recognize that it does not belong and begin to fight it by making antibodies. Importantly, the protein by itself does not give you COVID-19.

Basically, the mRNA is preparing your body to fight a COVID-19 infection without ever getting the infection. The mRNA “instructions” are rapidly degraded and do not last more than a couple of days following vaccination.

Some media reports have suggested that mRNA can impact a woman’s fertility: these reports have no basis whatsoever in science; there is no relationship between this vaccination and either fertility or pregnancy.

There are small differences in how these vaccines were made and some of the components of the vaccine, but these differences do not have any impact for the vaccine recipient. Both are safe and remarkably effective.

One difference is the period of time between getting the first and second dose:

  • For the Pfizer vaccine: 21 days after the first dose
  • For the Moderna vaccine: 28 days after the first dose

Other differences are how the vaccines are stored and the tiny fat molecules (lipids) that coat the mRNA to help it make its way into your cells. There are no other functional differences or variations in effectiveness or safety.

A vector vaccine contains the genetic material of a safe virus (such as the adenovirus) that has been created so that it cannot replicate and therefore cannot cause disease. The Johnson & Johnson / Janssen COVID-19 vaccine is a vector vaccine, and so are some other COVID vaccines in development. The gene encoding the coronavirus spike protein was spliced into this inert viral backbone.

When you receive this vaccine, the adenovirus rapidly transits to muscle cells in your arm (where the injection occurred), allowing the spike protein to be synthesized. When your body produces this protein, the immune system will recognize that it does not belong and begin to fight it by making antibodies. Just as with the mRNA vaccines, the spike protein itself does not give you COVID-19.

It’s good, especially for people who have egg allergies. These vaccines are as simple as you can get in a vaccine. That simplicity is a good thing. It means that the vaccine is safe for people who have had allergic reactions to other vaccines in the past. It also allows people who are immunocompromised or pregnant to receive the vaccine.

It’s all about availability and storage. The Pfizer vaccine needs to be kept at -112 degrees Farenheit until 2 weeks before use. In contrast, the Moderna vaccine is kept in a standard freezer and the Johnson and Johnson vaccine is stored in a refrigerator. This is one of the primary reasons why some places are giving people one vaccine over the other. The Moderna vaccine can also be kept longer after it thaws, while the Pfizer vaccine has to be used within a few days.

No. Each of the approved vaccines have received authorization by the FDA, and accomplish the same goal: to keep you from getting the virus that causes COVID-19. One vaccine isn’t better than the other, they are just different in the way they accomplish this goal. The best vaccine to get is the one you’re offered first.

It’s very common for viruses to mutate or change, creating new variations. Actually, there are several variations of the virus that causes COVID-19 already in the United States and around the world. The variant that emerged in the UK may spread more easily, but it does not cause a different kind of disease.

Scientists are researching how the vaccines work against the variations, and so far have found the vaccines to still be effective, although efficacy may be somewhat diminished. This is just one more reason why getting vaccinated as soon as it is offered to you is an excellent idea.

We know that these vaccines are very successful at preventing people from getting sick with coronavirus disease (COVID). What we don’t know is whether they prevent people from getting the virus at all, although new data indicate the good news that they do this as well.

Even if a vaccinated person caught the virus, they would almost certainly not have symptoms, and so the amount of virus they would spread through coughing and sneezing would be much less. It is for this reason, however, that people who are vaccinated still need to wear a mask and stay 6 feet apart from others.

About vaccine distribution

The Centers for Disease Control and Prevention (CDC) gives guidance, and then the state and local governments make plans for distribution.

In our area, the City of Philadelphia/Philadelphia Department of Public Health are responsible for the instructions on who goes first, second, and third, and where and how the vaccine is distributed. Many of the hospitals and healthcare providers have been given vaccine supplies so that healthcare workers and high-risk patients are able to get the vaccine as quickly as possible. The government is also giving pharmacies like Rite Aid doses of the vaccine to distribute to community members, and they are opening mass vaccination sites such as the Convention Center.

The distribution plan is updated frequently, so we recommend checking the City’s website (or the website of the county where you live) regularly for those updates and to see if you’re eligible.

No. Each hospital or doctor’s office may have its own policy. Whether or not an employee has been vaccinated, they will still follow current guidelines such as wearing a mask and goggles, and keeping 6 feet of distance whenever possible.

Anyone 12 years old and up in Philadelphia is now eligible to receive the COVID vaccine.

The supply of vaccines in Philadelphia mostly comes from the City of Philadelphia. Other counties in the area receive their own supplies and follow their own distribution plans. The local government determines how much each distribution site gets, when they get it, and who is eligible to get the vaccine. Check your local county’s website for up-to-date information.

Temple Health is offering vaccinations to anyone 16 years old and up who lives or works in Philadelphia, as well as to Pennsylvania residents. Find out how to schedule a vaccine appointment.

The City of Philadelphia is running mass vaccine clinics to Philadelphia residents. Learn more and register for an appointment.

There is also a federal program that allows retail pharmacies to get vaccines and distribute them locally. Search vaccinefinder.org/search to find out if a pharmacy near you has the vaccine available.

Other vaccine clinics around Philly include those operated by:

No. There is no tracking device or microchip in the vaccine. The only ingredients in the vaccine are those that will help prevent you from getting COVID-19. On the outside of the vaccine vial, there is a chip so that doses can be tracked to the location where they’re distributed. But this chip does not go inside the vaccine, nor inside your body.

On April 13, 2021, out of an abundance of caution, the FDA paused the use of the Johnson & Johnson vaccine to review data involving 6 reported U.S. cases (out of a total of over 6 million doses given) of a rare yet serious type of blood clot in people after receiving it.

Then on April 25, the CDC and FDA announced to resume the use of the Johnson & Johnson COVID vaccine. A review of the data showed that the potential benefits outweigh its known and potential risks. The CDC says that women younger than age 50 should be aware of the rare but increased risk of thrombocytopenia syndrome (TTS) following the Johnson & Johnson vaccine, and that there are other vaccine options available. Learn more from the CDC.

That said, it is important to be aware that people who have received the J&J vaccine who develop a severe headache, abdominal pain, leg pain or shortness of breath within 3 weeks after vaccination should call their doctor.

About receiving the vaccine

The vaccine is given through an injection (a shot) in the muscle in your upper arm. It’s the same way most people get a flu shot. A trained medical professional such as a doctor, nurse or pharmacist will give you the injection.

After you receive the vaccine, you will stick around for about 15 minutes to make sure that you do not have an allergic reaction. Please note that these are extremely rare! However, if there are any problems or you have questions, healthcare professionals will be around to care for you. Before you leave, you will be given instructions about how to schedule your second dose.

The most common side effect is arm soreness and redness, which can last a few days, or even a week or two after the vaccination.

With the mRNA vaccines from Moderna and Pfizer, side effects are more common after the second dose than the first dose. Tiredness, headache, muscle aches and fever can happen with both doses, but are more common with the second dose.

For most people, these symptoms have lasted no longer than a day. The side effects do not mean that you have COVID-19, but rather evidence that your body is making a good response to the vaccine.

Importantly, if you do NOT have symptoms, there is no need to worry: your body is making an effective response as well, you just happen to be in the lucky group to not have these side effects. Learn more about potential side effects.

The FDA has recommended that you DO NOT take pain medicine BEFORE getting the vaccine. Once you get the vaccine, if you develop side effects like arm pain or fever, then you can take medicine, such as Aspirin, Motrin or Tylenol.

No. There were no cases of severe allergic reactions (also called anaphylaxis) in either the Pfizer or the Moderna vaccine clinical trials. Severe allergic reactions have happened to a few people since the public rollout, but vaccine administrators were there and prepared to handle it.

When you’re vaccinated, you will wait for at least 15 minutes to make sure that you do not have an allergic reaction. There is also epinephrine (EpiPen©) kept on-site to treat someone if they do have an allergic reaction.

If you have a severe allergic reaction to the first dose, it’s recommended that you do not get the second dose. If you have had a severe allergic reaction to a vaccine or to other injections in the past, talk to your doctor about whether you should get the COVID vaccine.

Both mRNA vaccines (Pfizer and Moderna) are two doses. Unless you have a severe allergic reaction, there are no common reasons to miss a second dose. The second dose is important to ensure that you get maximal benefit from the vaccine.

Scientists and doctors believe most people who get the virus have antibodies that last 2 to 3 months. The risk that you catch the virus again within those 90 days is very low. The CDC guidance says that people who have had the virus can wait to get the vaccine for those 90 days.

But if you’re 14 days past your positive test and your symptoms have gone away, you can get the vaccine right away. For the second dose of either the Pfizer or Moderna vaccine, you should still get it as close to the 21- or 28-day follow-up interval as possible. Just make sure you’re not feeling symptoms anymore so that you avoid passing the virus to the person giving you your vaccine.

If you’ve had Bell’s palsy in the past, it does not prevent you from getting the vaccine. You should still get the vaccine. The only reasons to not get the vaccine are a history of severe allergic reactions or anaphylaxis from other vaccines. If you have concerns, talk to your doctor about what is best for you.

There is limited data available about how the mRNA vaccines affect people who are pregnant or breastfeeding. However, experts — including all pediatric medical societies —believe that based on how mRNA vaccines work, it’s unlikely that pregnant people are at a higher risk of side effects. If you’re pregnant or nursing, talk to your doctor to help make the decision on whether to get vaccinated.

The decision to receive the vaccine should be made with the help of your doctor. Typically, the risk of vaccine side effects is no different for people who have these conditions. In fact, sometimes those with weaker immune systems will have fewer side effects from vaccines.

But the risk of more severe illness from COVID-19 is higher for people who have these conditions, and thus the general recommendation is for individuals with immunological disorders to still get the vaccine.

Yes, you’re eligible to be vaccinated. Reach out to your clinical trial principal investigator first to let them know you’ve been invited to get vaccinated and that you intend to. Once you’ve been vaccinated, you cannot join a clinical trial later on.

Once you’re vaccinated, you are much, much safer from getting sick with COVID, but it remains possible that you may still be able to pass the virus to someone else. We still need to wear masks and stay 6 feet apart. All the precautions in place need to remain in place until a high percentage of people are vaccinated. But the vaccines mean that we are closer than ever to ending the pandemic.

If you got your vaccine, encourage your friends and family to do so as well, and refer them to this site if they have questions you cannot answer. You can also refer to the CDC’s latest guidelines once you’re fully vaccinated.

About vaccine clinical trials and the development process

The first 3 vaccines available to the public are from the pharmaceutical companies Pfizer/BioNTech, Moderna, and Johnson and Johnson. These vaccines have gone through safety trials just as other vaccines have. Tens of thousands of people received them during the clinical trials’ phases, and now millions have been vaccinated with each.

With the exception of a very small number of allergic reactions (which can be easily addressed and would occur during the short observation period after vaccination), NO serious or unexpected side effects have occurred in any of these millions of people.

These 3 vaccines have been shown to be effective, meaning that the vast majority of people who get them develop immunity against COVID-19. Specifically, they’re immune from infection by SARS-CoV-2, the virus that causes COVID-19.

The easy answer is that we had no choice: thousands of people were dying every day. By comparison, the previous record for fastest vaccine development was 4 years. A number of things made the process happen faster this time:

  • The mRNA technology that is used in the Pfizer and Moderna vaccines had been in development for more than 10 years already. They just incorporated this particular coronavirus strand into the development process in the last year.
  • Researchers were able to evaluate the safety and effectiveness of the vaccines at the same time instead of one after another.
  • Everyone worked together on a high priority goal. Pharmaceutical manufacturers partnered with each other, and got the government involved very early on.
  • There was no downtime between the trial phases. The researchers, scientists, pharmaceutical companies and government agencies made sure that there were no delays in any of the steps.
  • Tens of thousands of people volunteered immediately to participate in the clinical trials.

Importantly, while these vaccines were expedited, no corners were cut in any of the safety trials. The only thing that was cut was red tape.

Yes. Members of the Food and Drug Administration (FDA) advisory panel, which is the group that releases the authorization for the vaccines, are not all employed by the federal government. They’re scientists and researchers from academic and clinical organizations around the country who are looking at this with independent eyes.

The CDC guidelines have changed during this pandemic, which may seem like they’re indecisive or cannot be trusted. What this really means is that information about this virus is changing every day, so the CDC’s advice may also change when they find out more information.

All of the companies have been open about releasing their data and evidence. Their research has been and will continue to be peer reviewed by scientists and physicians who are not part of that company to ensure accuracy, transparency, and feedback.

During a public health emergency, the U.S. Food and Drug Administration (FDA) may allow unapproved medical products to be used to diagnose, treat or prevent serious diseases when there are no adequate, approved and available alternatives. If the evidence shows that patients have benefited from the medical product in clinical trials, and that the drugs or vaccines are safe, the agency can issue an EUA to make it available to the public.

The first vaccines from Pfizer/BioNTech and Moderna showed positive results in clinical trials. The companies showed these results to the FDA, and they gave these vaccines an EUA. This made the vaccines immediately available while more data continues to be collected. Once enough data is reported, the FDA evaluates the vaccines for approval.

Page last updated May 19, 2021.