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Are COVID-19 vaccines safe and effective? How were they tested and approved?

Last Updated: 09/01/2021

All currently approved or authorized COVID-19 vaccines are safe, effective, and will help protect you from getting COVID-19.

Currently, the Pfizer, Moderna, and Johnson & Johnson vaccines are being administered in New Jersey.

The Pfizer vaccine is recommended for individuals 12 years of age and older, and the Moderna and Johnson & Johnson vaccines are recommended for individuals 18 years and older. For all vaccinations, consent from a parent or guardian is required for minors.

A third dose of the Pfizer or Moderna COVID-19 vaccines is recommended for people with moderately to severely compromised immune systems who have received the initial two-dose vaccine series.

What to Know About Available COVID-19 Vaccines

COVID-19 vaccines are safe, effective, and will help protect you from getting COVID-19. Millions of people in the United States have received COVID-19 vaccines under the most intense safety monitoring in U.S. history.

  • COVID-19 vaccines will not give you COVID-19. The vaccines cannot give you COVID-19. None of the COVID-19 vaccines in use in the United States use the live virus that causes COVID-19.
  • COVID-19 vaccines will not cause you to test positive on COVID-19 viral tests. Vaccines won't cause you to test positive on viral tests, which are used to see if you have a current infection.
  • Receiving a COVID-19 vaccine will not alter your DNA. COVID-19 vaccines do not change or interact with your DNA (genetic material) in any way. Both mRNA (Pfizer and Moderna) and viral vector (Johnson & Johnson's Janssen) COVID-19 vaccines deliver instructions to our cells to start building protection against the virus that causes COVID-19. However, the material never enters the nucleus of the cell, which is where our DNA is kept.
  • COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products. The safety and efficacy of a mixed-product series has not been evaluated. Both doses of the series should be completed with the same product.
  • You should be vaccinated even if you already had COVID-19. Evidence is emerging that people get better protection by being fully vaccinated compared with having had COVID-19. One study showed that unvaccinated people who already had COVID-19 are more than 2 times as likely than fully vaccinated people to get COVID-19 again.
  • Getting vaccinated can help prevent getting sick with COVID-19. There is no way to know how COVID-19 will affect you. If you get sick, you also may spread the disease to friends, family, and others around you while you are sick. COVID-19 vaccination helps protect you by creating an immune response without having to experience sickness.

Vaccine Trials and Testing

COVID-19 vaccines that are approved or authorized for use have gone through clinical trials involving tens of thousands of participants to determine their safety and efficacy.

The known and potential benefits of approved vaccines outweigh the known and potential harms of becoming infected with COVID-19.

The FDA has fully approved and licensed Comirnaty, previously known as the Pfizer vaccine for those 16 and older and has authorized the Moderna and Johnson & Johnson vaccines for emergency use. The Pfizer vaccine continues to be available under emergency use authorization for individuals ages 12 through 15 and as a third dose for individuals who have aremoderately or severelyimmunocompromised (weakened immune system).

The two-dose Pfizer-BioNTech (Pfizer) COVID-19 vaccine is FDA-authorized to prevent COVID-19 in individuals 12 years of age and older and to provide a third dose to individuals who have been determined to have certain kinds of immunocompromised (weakened immune system). The vaccine is FDA-approved as Comirnaty to prevent COVID-19 in individuals 16 years of age and older.

The two-dose Moderna COVID-19 vaccine is FDA-authorized to prevent COVID-19 in individuals 18 years of age and older and to provide a third dose to individuals who have been determined to have certain kinds of immunocompromise.

The one-dose Janssen (Johnson & Johnson) COVID-19 vaccine is FDA-authorized to prevent COVID-19 in individuals 18 years of age and older.

More information from the FDA about these three vaccines can be found here:

For the Comirnaty or Pfizer-BioNTech vaccine, please consult these FDA fact sheets:

For the Moderna vaccine, please consult these FDA fact sheets:

For the Janssen (Johnson & Johnson) vaccine, please consult these FDA fact sheets:

Clinical Trials

The FDA has approved Pfizer-BioNtech's Comirnaty vaccine and has issued Emergency Use Authorizations for the Pfizer-BioNTech vaccine, Moderna vaccine, and Johnson & Johnson's Janssen vaccine. Additional vaccines are in Phase 3 clinical trials. Visit the CDC's "Developing COVID-19 Vaccines" page for more details on the development and approval process.

Clinical trials are research studies performed in people that are aimed at evaluating a medical, surgical, or behavioral intervention. They are the primary way that researchers find out if a new treatment, like a new drug, vaccine, or medical device is safe and effective in people.

Currently, clinical trials are evaluating COVID-19 vaccines in many thousands of study participants to generate scientific data and other information for the FDA to determine their safety and efficacy. These clinical trials are being conducted according to rigorous safety standards. For detailed information, visit this CDC page.

Side Effects

After receiving an injection of a COVID-19 vaccine, you will be observed for 15 minutes by healthcare staff to monitor any side effects. Observation may be longer (30 minutes) if you have a history of anaphylaxis (severe allergic reaction).

Like many vaccines, a COVID-19 vaccine may cause some temporary discomfort. In addition to a sore arm, side effects of the vaccines may include tiredness, headache, muscle pain, chills, joint pain, fever, injection site swelling, injection site redness, nausea, feeling unwell, and swollen lymph nodes.
There is a small chance that vaccines could cause a severe allergic reaction. A severe allergic reaction would usually occur within a few minutes to one hour, which is why all individuals should be observed for at least 15 minutes after vaccination and 30 minutes if they have a history of a severe allergic reaction due to any cause.

There is a remote chance that the Johnson & Johnson vaccine could increase risk of blood clots with low levels of platelets. Nearly all reports have been in adult women younger than 50 years old. After a temporary pause in the use of the Johnson & Johnson vaccine, the FDA and CDC determined that the vaccine's known and potential benefits outweigh its known and potential risks and recommended use of the Johnson & Johnson vaccine resume.

There have been reports of cases of inflammation of the heart – called myocarditis and pericarditis – happening after mRNA COVID-19 vaccination (Pfizer and Moderna). In most cases, patients have responded well to medications and rest and had prompt improvement of symptoms. Reported cases have occurred predominantly in male adolescents and young adults 16 years of age and older. The CDC continues to recommend COVID-19 vaccination for everyone 12 years of age and older given the greater risk of other serious complications related to COVID-19.

The CDC and FDA are monitoring rare reports of Guillain-Barré syndrome (GBS) after the Johnson & Johnson vaccine. The majority of cases have occurred in males aged 50 and older about two weeks after vaccination, mostly within six weeks.

For more information on vaccine safety, visit https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety.html and speak with your healthcare provider.

Source: https://www.state.nj.us/health/cd/documents/topics/NCOV/Public_FAQ.pdf; https:/www.cdc.gov/coronavirus/2019-ncov/vaccines/safety.html; https://www.fda.gov/coronavirus-disease-2019-covid-19/covid-19-vaccines