Frequently Asked Questions

Q. I have doubts about the Covid vaccines because they were developed so quickly.

A. It’s true that these vaccines were developed a lot more quickly than traditional vaccines, but the development wasn’t rushed. Several factors made it possible. Scientists already knew a lot about coronaviruses because they cause other diseases. They also started working on the mRNA technology used in the Pfizer and Moderna vaccines more than 10 years ago with the goal of using it to develop vaccines for new diseases quickly in an emergency. Once the Covid vaccines were developed, researchers went through all the usual steps of testing them, but saved time by doing them in parallel instead of one after the other.

Q. How do we know the vaccine is safe and effective?

A. The Covid-19 vaccines available in the United States have been tested in clinical studies of tens of thousands of people and in real-world observational studies of millions of people. We know from these studies that the available vaccines are almost 100% effective in preventing hospitalization and death from Covid, and that they are also highly effective in preventing most Covid disease and new infections.

The safety and effectiveness of the vaccines is constantly being evaluated. But it’s already clear, after 100s of millions of doses, that it’s far safer to be vaccinated than to risk getting Covid, which can be deadly even to young people.

Q. Are there important differences between vaccines?

A. The Moderna and Pfizer vaccines are made with similar technology and provide similar high levels of protection against Covid. These vaccines require two doses several weeks apart.

The Johnson & Johnson vaccine is made with older technology and was designed to require only one dose. Recent studies suggest it is less effective against new strains of the coronavirus. Rare, but potentially serious, side effects have also been linked to this vaccine. For this reason, the Pfizer or Moderna vaccine is recommended for most people.

Q. What do we know about side effects?

A. When questions come up about illnesses that might be vaccine related, they are investigated and the public is given detailed information about the risks of taking the vaccine compared to the risks of getting COVID-19.

The most common side effects are similar to the ones many people have from other vaccines: pain or tenderness at the site of the shot and tiredness and flu-like symptoms about a day later.

Some people have developed severe allergic reactions after getting a Covid-19 vaccine. These reactions are rare (less than 5 per million). For your safety, you will be asked about your history of allergy before you are given a vaccine and you will be observed for up to 30 minutes afterward to be sure you are okay. In the unlikely event that you do have a reaction, emergency medical providers will be on site to treat you immediately.

Q. I have doubts about the Covid vaccines because they were developed so quickly.

A. It’s true that these vaccines were developed a lot more quickly than traditional vaccines, but the development wasn’t rushed. Several factors made it possible. Scientists already knew a lot about coronaviruses because they cause other diseases. Scientists also started developing the technology used in the Pfizer and Moderna vaccines 10 years ago with the goal of using it to develop vaccines for new diseases quickly in an emergency. Once the Covid vaccines were developed, researchers went through all the steps of testing them, but saved time by doing them in parallel instead of one after the other.

Q. How do we know the vaccine is safe and effective?

A. The Covid-19 vaccines available in the United States have been tested in clinical studies of tens of thousands of people and in real-world observational studies of millions of people. We already know from these studies that all three vaccines are almost 100% effective in preventing hospitalization and death from Covid, and that they are nearly as effective in preventing mild Covid and new infections. 

Studies are still going on to answer other questions about the vaccines, like how well they work in children and how long the protection lasts. But it’s already clear, after 100s of millions of doses, that it’s far safer to be vaccinated than to risk getting Covid, which can be deadly even to young people.

Q. What do we know about side effects?

A. When questions come up about illnesses that might be vaccine related, they are investigated and the public is given detailed information about the risks of taking the vaccine compared to the risks from getting COVID-19.

The most common side effects are similar to the ones many people have from other vaccines: pain or tenderness at the site of the shot and tiredness and mild flu-like symptoms about a day later. 

Some people have developed severe allergic reactions after getting a Covid-19 vaccine. These reactions are rare (less than 5 per million), but for your safety, you will be asked about your history of allergy before you are given a vaccine and you will be observed for up to 30 minutes afterward to be sure you are okay. In the unlikely event that you do have a reaction, emergency medical providers will be on site to treat you immediately.

So far, no other serious side effects have been definitely linked to the vaccines. Blood clots have been found in some women who were given the Johnson & Johnson vaccine and some children and adolescents who got the Pfizer or Moderna vaccine developed inflammations of the heart. These conditions are very rare and are being investigated, but they don’t appear to be more common in vaccinated people. More importantly, Covid can cause both conditions and the risk of developing them is much higher if you have Covid than if you are vaccinated.

Q. I read the vaccine is 95% effective. Does that mean there is still a 5% chance I could get Covid?

A. No. It means that the risk of getting Covid is 95% lower for a vaccinated person compared to an unvaccinated person.

Q. I heard I could still get infected and transmit the virus to someone else, even if I’m vaccinated. Is that true?

A. It is possible, but the chance of that happening if you are vaccinated is much smaller than if you are not vaccinated. 

Q. Is it true that messenger RNA (mRNA) in the Pfizer and Moderna vaccines can interfere with our own DNA?

A. This isn’t true. The vaccines’ mRNA teaches our cells to recognize the coronavirus and attack it, but it can’t interact with DNA or cause genetic changes because it doesn’t enter the nucleus of the cell, where DNA is located. The mRNA is also broken down quickly and doesn’t accumulate in the body.

Q. Is it true that the vaccines can interfere with a woman’s ability to get pregnant?

A.This is a common question, but there is no evidence that women in clinical trials or the millions of women who have been vaccinated have had trouble getting pregnant. Medical organizations like the American College of Obstetricians and Gynecologists recommend vaccination for women who are pregnant or trying to become pregnant.

Q. I am pregnant. Is it ok for me to be vaccinated?

A. Yes, it is recommended you do! Although the effects of vaccination during pregnancy are still being studied, we know already that women who are infected by the coronavirus while they are pregnant are more likely to have severe Covid and to be hospitalized. We also know that Covid increases the risk of premature birth. Because of this, experts believe it is safer for pregnant women to be vaccinated than not to be. It is also important to get started with prenatal care in the first 2 months of pregnancy. You may want to discuss whether to get the COVID-19 vaccine with your pregnancy medical provider.

Q. I already had Covid, so why would I need the vaccine?

A. Vaccination is recommended for people who have had Covid because scientists believe that the immunity from vaccination is stronger and lasts longer than the immunity from having the disease. 

Q. Will the vaccine protect me against variant strains of the coronavirus?

A. The virus is constantly evolving new variants, but so far the vaccines are giving good protection against the strains that are circulating in California. In fact, being vaccinated helps stop the virus from developing new strains. 

Q. How much will it cost to be vaccinated?

A. Nothing. The Covid-19 vaccination is free.