Vaccines FAQ

Being vaccinated against COVID-19 helps the body develop a memory response to fight off the virus that causes COVID-19, without having to get the illness. COVID-19 vaccines also decrease the likelihood of severe illness or death if infection does occur. For more information, see Understanding How COVID-19 Vaccines Work (CDC).

The COVID-19 vaccines manufactured by Pfizer and Moderna are mRNA vaccines. After our cells make copies of the protein, they destroy the genetic material from the vaccine. Our bodies recognize that the protein should not be there and build T-lymphocytes and B-lymphocytes (white blood cells) that will remember how to fight the virus that causes COVID-19 if we are infected in the future.

mRNA vaccines do not contain a live virus and do not carry a risk of causing disease in the vaccinated person. mRNA from the vaccine never enters the nucleus of the cell and does not affect or interact with a person’s DNA. For more information on mRNA vaccines, see Understanding and Explaining mRNA COVID-19 Vaccines (CDC).

The COVID-19 vaccine manufactured by Janssen (Johnson & Johnson) is a viral vector vaccine. Viral vector vaccines use a modified version of a different virus (the vector) to deliver important instructions to our cells. For COVID-19 viral vector vaccines, the vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then use the cell’s machinery to produce a harmless piece of the virus that causes COVID-19. This piece is known as a spike protein and it is only found on the surface of the virus that causes COVID-19.

The cell displays the spike protein on its surface, and our immune system recognizes it doesn’t belong there. This triggers our immune system to begin producing antibodies and activating other immune cells to fight off what it thinks is an infection. At the end of the process, our bodies have learned how to protect us against future infection with the virus that causes COVID-19. For more information, see Understanding Viral Vector COVID-19 Vaccines.

• birth year (not reported for people over 80 years old)
• sex
• the county where the vaccine is administered.

Serious adverse events after COVID-19 vaccination are rare, and the FDA has determined that the benefits of the vaccines far outweigh the risks. The risk of severe disease, hospitalization, or death from COVID-19 in unvaccinated/unboosted persons is much greater than any risk of serious side effects from the COVID-19 vaccines themselves. Due to the risk of a rare (but serious) side effect of the J & J vaccine, the CDC recommends that the Pfizer or Moderna vaccine is used in all eligible persons, including for booster doses. The J & J vaccine is still authorized by the FDA for those who prefer it or who are not able to receive the Pfizer or Moderna vaccine. Getting any of the three available vaccines is better than being unvaccinated. For more information, see Things to Know About COVID-19 Vaccines (CDC).  

For more information about the risks associated with the J&J vaccine, please see Have there been any serious side effects from the vaccines? or talk with your healthcare provider.  

For more information about risks associated with the Novavax vaccine, please see the CDPH fact sheets in English or Spanish . 

• No preservatives like thimerosal or mercury or any other preservatives.  

• No antibiotics like sulfonamide or any other antibiotics.  
• No medicines or therapeutics like ivermectin or any other medications.  
• No human or animal tissues like aborted fetal cells, gelatin, or any materials from any animal.  
• No food proteins like eggs or egg products, gluten, peanuts, tree nuts, nut products, or any nut byproducts (COVID-19 vaccines are not manufactured in facilities that produce food products).  
• No metals like iron, nickel, cobalt, titanium, rare earth alloys, or any manufactured products like microelectronics, electrodes, carbon nanotubes or other nanostructures, or nanowire semiconductors.  

• No latex. The vial stoppers used to hold the vaccine also do not contain latex.  

Some people experience side effects after getting the COVID-19 vaccine. These side effects are common as the body builds cells to defend against COVID-19. They usually develop within 3 days of getting the vaccine and go away after a day or two. Side effects are more common after the second dose from the primary series.

Side effects in the arm (or thigh in the youngest children) where you got the vaccine may include:

• Pain
• Redness
• Swelling

Side effects throughout the rest of your body may include:

• Tiredness
• Headache
• Muscle pain
• Chills
• Fever
• Nausea
• Irritability, crying, sleepiness, and loss of appetite in infants and younger children

Yes. COVID-19 vaccination is recommended for all persons ages 6 months and over, including persons who are pregnant, breastfeeding, trying to become pregnant, or may become pregnant in the future. Pregnant and recently pregnant persons are more likely to get severely ill with COVID-19 compared to non-pregnant persons. In addition, pregnant people who have COVID-19 are at increased risk of pre-term birth (delivering a baby before 37 weeks).

Getting a COVID-19 vaccine can help protect pregnant and/or breastfeeding persons from severe illness from COVID-19. 

• COVID-19 vaccines have been carefully studied in pregnant persons. There is NO increased risk of miscarriage or other negative outcomes for pregnant persons OR the developing fetus.
• Vaccination during pregnancy protected BOTH pregnant person and their infants ages 0 to 5 months.
• There is NO evidence that any vaccines, including COVID-19 vaccines, cause fertility problems in women or men. 
• Breastfeeding is SAFE after vaccination. Breastfeeding persons who have received COVID-19 mRNA vaccines (Moderna and Pfizer) have antibodies in their breastmilk, which can help protect their babies. 
  
  

For more information, please review COVID-19 Vaccines While Pregnant or Breastfeeding (cdc.gov), Guidance for Vaccination during Pregnancy (CDPH), and this statement from the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM).

• V-safe app from the CDC is a smartphone-based, after-vaccination health checker for people who have received the COVID-19 vaccine. V-safe uses text messaging and surveys to check in with COVID-19 vaccine recipients after vaccination. Simply put, anyone with symptoms enters their information into V-Safe so that researchers can continue to study the safety of the vaccine on all populations.
• The Vaccine Adverse Event Reporting System (VAERS) is a national system used by the CDC and the FDA. This system collects reports from healthcare professionals, vaccine manufacturers, and the public regarding any adverse events that may happen after vaccination.
• National Healthcare Safety Network (NHSN) is an acute and long-term facility monitoring system that reports to the Vaccine Adverse Events Reporting System (VAERS).
• Vaccine Safety Datalink (VSD) is a network of nine healthcare organizations from across the US that conduct active surveillance and research. This system is used to aid in determining if possible side effects identified in the VAERS are actually related to the vaccine.
• Clinical Immunization Safety Assessment (CISA) Project is a collaboration between seven medical research institutions and the CDC. CISA provides consultation on a case by case basis, and conducts research about vaccine safety.

Please wait until your quarantine period is over before getting vaccinated or boosted. This helps reduce the risk of potentially spreading the virus that causes COVID-19 to others during the vaccination visit.

Please continue to follow all COVID-19 safety measures and quarantine guidance.

The CDC does not recommend taking medications that treat fever and pain, such as acetaminophen or ibuprofen, before your vaccine to prevent side effects. These medicines might affect how well your body’s immune system responds to the vaccine. If you take these medications regularly for another health condition, talk to your healthcare provider before skipping any doses.

You can ask your healthcare provider about whether you can take these medications after vaccination for symptoms such as fever or arm pain. To soothe arm pain, the CDC also recommends applying a clean, cool, wet washcloth over the area where you feel discomfort and exercising your arm. If you experience fever, drink plenty of fluids and keep your body cool.

If you have COVID-19 or tested positive for SARS-CoV-2, you should wait to get your second dose until your symptoms have resolved (if you have symptoms) AND until you have finished your isolation period. According to the CDC, it’s OK to consider delaying a primary series or booster dose for 3 months after having COVID-19. Sometimes this will require rescheduling your second dose, but there is no need to retake the first dose.

Because vaccines are not 100% effective, the number of infections in vaccinated persons will increase as the number of people who are fully vaccinated goes up. People with COVID-19 who have completed a primary vaccine series, especially if they are up to date with booster recommendations, are less likely to develop serious illness than those who are unvaccinated and get COVID-19. Even when up-to-date people develop symptoms, they tend to be less severe symptoms than in unvaccinated or unboosted people. This means they are much less likely to be hospitalized or die than people who have not completed a primary vaccine series or gotten boosted. However, vaccinated persons who get COVID-19 can spread COVID-19 to others.

For information on booster doses, see Who should get a COVID-19 booster dose?

Pfizer/BioNTech  

• 46,331 enrolled  

• 153 clinical sites in 39 United States  
• Racial/ethnic distribution:  

• 70% White  
• 13% Hispanic/Latino (>5.5k)  
• 10% African American/Black (>4k)  

• 6% Asian  
• 1% Native American  

• Age distribution:  

• 45% ages 56-85  

Moderna 

• 30,000 enrolled  
• 89 clinical sites in 32 United States  
• Racial/ethnic distribution: 

• 63% White  
• 20% Hispanic/Latino (6k)  

• 10% African American/Black (3k)  
• 4% Asian  
• 3% All others  

• Age distribution: 

• 39% ages 45-64  

• 25% ages 65+  

Janssen (Johnson & Johnson) 

• 43,783 enrolled 
• Racial/ethnic distribution: 
• 74% White 
• 15% Hispanic/Latino, 
• 13% Black/African American 
• 6% Asian 
• 1% American Indian/Alaska Native 

• Age distribution: 

• 66% ages 18-59 
• 34% ages 60+ 

It’s OK to wait up to 3 months after having COVID-19 to get a booster dose. 

The updated booster was authorized by the FDA in August 2022 and may provide better protection against current variants.  

In alignment with the CDPH, visit MYTurn.ca.gov to find a location near you. You can also check with your healthcare provider or local pharmacy to see if vaccination walk-ins or appointments are available. You can also find vaccination locations at Where to get a Vaccine in Alameda County.

Please note that you do not need a note from your healthcare provider to receive aCOVID-19 booster. If you are part of any of the groups eligible for a COVID-19 booster, you may self-attest and receive a booster.

The COVID-19 vaccines are working well to prevent severe illness, hospitalization, and death due to COVID-19. Cases by vaccination status can be viewed here: https://covid19.ca.gov/state-dashboard/#postvax-status. However, there is reduced protection over time, especially among populations such as older adults and those with underlying medical conditions, against mild and moderate disease. Make sure to stay up to date by getting booster doses when eligible.  

No. It is a moral and public health imperative to ensure that all individuals residing in the United States have access to the vaccine. Alameda County and the Department of Homeland Security (DHS) encourage all individuals, regardless of immigration status, to receive the COVID-19 vaccine once eligible under local distribution guidelines. For more information, please see DHS Statement on Equal Access to COVID-19 Vaccines and Vaccine Distribution Sites.

There is no cost associated with getting vaccinated against COVID-19— regardless of insurance, immigration status, or vaccine phase at Alameda County-operated or supported clinics. If you choose to receive a vaccine at a pharmacy or health care provider's facility, remember to ask if there is an out-of-pocket cost associated with the vaccination, if they accept insurance, or what cost coverage options are available for people who are uninsured, a non-U.S. citizen or have already started your vaccination process elsewhere.

• Photo Identification (ID). Your photo ID does not have to be government issued.
• Appointment Confirmation. If you have an appointment, print the confirmation, or provide it on your phone.
• Mask. Please remember to wear a mask and practice social distancing.

• The Pfizer-BioNTech vaccine consists of two doses given at least 21 days apart. 
• The Moderna vaccine consists of two doses given at least days apart. 
• The Novavax vaccine consists of two doses given 21 days apart. 
• The Johnson & Johnson vaccine consists of one dose. 

The CDC allows up to 8 weeks between doses of Pfizer, Moderna and Novavax for certain persons, such as males ages 12 to 39 years due to the small risk of myocarditis after receiving these vaccines. This longer interval between doses may also increase vaccine effectiveness. Talk with your healthcare provider if you have questions about when you should get your second dose.  

Please bring your COVID-19 vaccination record card with you to your second vaccination appointment. It is recommended that you make a backup copy of your COVID-19 vaccination record card, such as taking a picture of your vaccination card with your phone.     

Additionally, your first vaccine dose is recorded in the California Immunization Registry (CAIR). Therefore, at your second dosing appointment you can ask your vaccine administrator pull up your information on CAIR to ensure vaccine mixing does not occur.  

Yes. If you have symptoms, you should get tested immediately and isolate if your test is positive. If you have been exposed to someone with COVID-19, you should get tested 3 to 5 days after the exposure and isolate if your test is positive. The vaccine does not affect the results of COVID-19 diagnostic tests, such as PCR or antigen tests. Anyone with symptoms of COVID-19 should be tested even if they were recently vaccinated.

The vaccine will protect you from developing severe illness, but it may not stop you from spreading COVID-19 to others if you become infected. Until we get enough people vaccinated to protect our entire community, it is critical that everyone—even those who have been vaccinated—continue to follow other COVID-19 prevention guidance, such as wearing masks. It is also important to get tested if you experience symptoms of COVID-19 or are exposed to someone who has COVID-19 and isolate if your test is positive.

The dosage of vaccine for children ages 5-11 is smaller than the dosage for those ages 12 and older, and it is given with a smaller needle. Children ages 5-11 will receive 1/3 of the dosage for teens and adults of the Pfizer vaccine. Children 5 years of age who receive the Moderna vaccine will receive ¼ of the dosage for teens and adults. Children ages 6-11 will receive half the dosage of Moderna as teens and adults.

Yes. The CDC recommends that children and adolescents ages 6 months and older get the vaccine, even if they’ve had COVID-19. People can get infected with COVID-19 more than once, and we don’t know how long someone is protected against getting infected again after recovering from the virus. Current antibody tests cannot tell us whether a person is protected from getting another COVID-19 infection. We also don’t know whether the immunity developed against one strain, such as Omicron, will provide enough protection against new variants.

If you are vaccinating your child after they have had COVID-19, they should wait until they are symptom-free, and their isolation period is over. According to the CDC, it’s OK to consider delaying a primary series or booster dose for 3 months after having COVID-19. If your child has a history of multisystem inflammatory syndrome in children (MIS-C), consider delaying vaccination until your child has recovered from being sick and for 90 days after they were diagnosed with MIS-C.

Serious adverse events after COVID-19 vaccination are rare. The FDA determined that the benefits of the vaccine far outweighs the risks. The risk of severe disease, hospitalization, or death from COVID-19 in unvaccinated/unboosted persons is much greater than any risk of serious side effects from the vaccines.  

The CDC recently changed its recommendations to allow up to 8 weeks between doses of Pfizer, Moderna and Novavax for certain persons, such as males ages 12 to 17 years due to the small risk of myocarditis after receiving these vaccines. This longer interval between doses may also increase vaccine effectiveness. For some children and youth, such as those who are immunocompromised or who have certain medical conditions, a longer time between first and second doses may not be recommended. Talk with your child’s healthcare provider if you have questions about when your child should get their second dose.  

The American Academy of Pediatrics has released statements on the importance of vaccinating children 6 months and older. For more information, see Things to Know About COVID-19 Vaccines (CDC).  

After getting a COVID-19 vaccine, children and youth may have some side effects, such as:

• Sore arm (or thigh in the youngest children)
• Feeling tired for a day or two
• Muscle aches or headache
• Low grade fever
• Chills
• Upset stomach
• Irritability, crying, sleepiness, and loss of appetite in infants and younger children

Most side effects are mild and will go away in a few days. Side effects can be more intense after the second shot in the primary series than the first. Side effects happen as the body is building protection against the virus, but they should go away in a few days. If side effects do not improve, contact your child’s healthcare provider.

There have been cases of myocarditis (heart inflammation) and pericarditis (inflammation of the sac around the heart) among youth after getting an mRNA vaccine like Pfizer and after getting Novavax. These have been mostly in male teens and young adults within a few days of getting the second dose of vaccine from the primary series. Since authorization, over 18 million doses of the Pfizer vaccine have been given to children ages 5 to 11, and the CDC has confirmed 20 cases of myocarditis in this age group, mostly after Dose 2. Most of the youth who received care responded well to medicine and rest and quickly felt better. There were no reported cases of myocarditis during the vaccine clinical trials for children ages 6 months through 4 years of age. The CDC and its partners are actively monitoring reports of myocarditis and pericarditis, by reviewing data and medical records, to learn more. Safety monitoring systems are in place to collect information if more cases are detected.   

Children and teens should seek medical attention right away if they have any of the following symptoms after receiving the COVID-19 vaccine:    

• Chest pain   
• Shortness of breath    
• Feelings of having a fast-beating, fluttering, or pounding heart.   

An 8-week interval between first and second doses may be a good choice for some persons, including males 12-17 years of age because of the small risk of myocarditis associated with mRNA vaccines and with Novavax. You can also visit the CDC’s Myocarditis and Pericarditis Following mRNA COVID-19 Vaccination webpage to learn more.  

There are systems in place to monitor for adverse events and side effects of the vaccine in real-time, including:

• Enroll in the V-safe app from CDC. Parents and guardians can enroll children and youth ages 5 years and older in V-safe and complete health check-ins on their behalf after they have been vaccinated for COVID-19. Anyone 16 and over can enroll themselves. V-safe is a smartphone-based, after-vaccination health checker for people who have received the COVID-19 vaccine. V-safe uses text messaging and surveys to check in with COVID-19 vaccine recipients after vaccination. Simply put, anyone with symptoms enters their information into V-Safe so that researchers can continue to study the safety of the vaccine on all populations. 
• The Vaccine Adverse Event Reporting System (VAERS) is a national system used by the CDC and the FDA. This system collects reports from healthcare professionals, vaccine manufacturers, and the public regarding any adverse events that may happen after vaccination.
• National Healthcare Safety Network (NHSN) is an acute and long-term facility monitoring system that reports to the Vaccine Adverse Events Reporting System (VAERS).
• Vaccine Safety Datalink (VSD) is a network of nine healthcare organizations from across the US that conduct active surveillance and research. This system is used to aid in determining if possible side effects identified in VAERS are actually related to the vaccine.

• Clinical Immunization Safety Assessment (CISA) Project is a collaboration between seven medical research institutions and the CDC. CISA provides consultation on a case by case basis, and conducts research about vaccine safety.
• Learn more about how the safety of the COVID-19 vaccine is ensured.

• Get very sick from COVID-19, including requiring hospitalization. Children with underlying medical conditions are at higher risk for severe illness, but one-third to one-half of children and teens who are hospitalized have NO underlying medical conditions
• Develop serious complications like multisystem inflammatory syndrome (MIS-C)—a condition where different body parts become inflamed, including the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal organs.
• Develop post-COVID complications, also called “long COVID”.
• Spread COVID-19 to others, including vulnerable members of their family.
• Miss school, sports, extracurricular activities and other important events if they get infected.

Vaccine doses are given by a child’s age, not their weight, because that’s how they were studied during clinical trials. Children and youth should receive a dose based on their age on the day of vaccination. Sometimes this means that the second dose will be higher than the first dose.

Yes! COVID-19 vaccines and other vaccines can be given at the same time. If your child has missed recent vaccinations due to the pandemic, now is a great time to get caught up. Talk to your healthcare provider if you have questions about your child getting multiple vaccines at once.

Children under age 12 need consent from a parent or legal guardian, and should be accompanied by a parent, legal guardian or qualified relative (ages 18 and older) to and from the vaccination site. A qualified relative is defined as a spouse, parent, stepparent, brother, sister, stepbrother, stepsister, half-brother, half-sister, uncle, aunt, niece, nephew, first cousin, or any person denoted by the prefix “grand” or “great,” or the spouse of any of the persons listed in this definition.

Youth ages 12 and older need consent from a parent or legal guardian, but they do not need to be accompanied by an adult to the vaccination site.

You may read the full CDPH Pfizer Vaccine Minor Vaccination Guidance online or a summary of the guidance below. The ACPHD Pfizer Minor Consent Guidance is available on this website under “Resources.” 

Per the California Department of Public Health Pfizer Vaccine Minor Consent Guidance, anyone younger than 18 years (a “minor”) must have a parent or legal guardian consent on their behalf prior to receiving the Pfizer COVID-19 vaccine. A Relative Caregiver (e.g., someone who is 18 years or older and lives with the minor such as a grandparent, aunt, uncle, or cousin) may provide consent after completing a Caregiver Affidavit Form. 

An emancipated minor may consent for himself/herself/themselves. 

Unaccompanied minors* may consent to their own medical care if all the following conditions are satisfied: 

1. The minor is 15 years of age or older. 
2. The minor is living separate and apart from the minor's parents or guardian, whether with or without the consent of a parent or guardian and regardless of the duration of the separate residence. 
3. The minor is managing their own financial affairs, regardless of the source of the minor's income. 

*Unaccompanied minors are defined in U.S. law as children who cross our borders and (1) have no lawful immigration status in the U.S., (2) have not attained 18 years of age, and (3) have no parent or legal guardian in the U.S. or no parent or legal guardian in the U.S. who is available to provide for their care and physical custody. 

The process for developing and authorizing vaccines is well established. No steps were skipped in developing the COVID-19 vaccines, including in the clinical trials for children and youth. However, some of the steps were performed at the same time, thus speeding up the process.

No. COVID-19 vaccines do not interact with or change your DNA in any way. 

The vaccines manufactured by Pfizer and Moderna are mRNA vaccines. mRNA vaccines do not contain a live virus and do not carry the risk of causing an infection in the vaccinated person. mRNA from the vaccine never enters the nucleus of the cell and does not affect or interact with a person’s DNA. 

Some people who menstruate have noticed changes in their menstrual cycle around the time they got their COVID-19 vaccine. However, people can experience health issues following vaccination that would have happened even if they did not get vaccinated. There is currently no research suggesting that that any of the COVID-19 vaccines affect menses or the onset of puberty. However, both stress and illness can cause irregular menstrual cycles, and in the first few years after people get their periods, it’s not uncommon for their cycles to be irregular. Using an additional method of birth control may be important for some after vaccination. 

According to the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics, there is no evidence that COVID-19 vaccines can affect the ability to get pregnant. While fertility was not specifically studied in the clinical trials of the vaccine, no loss of fertility has been reported among trial participants or among the millions who have received the vaccines since their authorization. In addition, no signs of infertility appeared in animal studies. 

Clinical trials of Pfizer COVID-19 vaccine were found to be safe and effective in protecting against severe illness, hospitalization, and death in children and youth ages 5-11 and 12-15.

Pfizer Clinical Trial Participant Summary, Children and Youth ages 5-11
Pfizer’s clinical trial for those ages 5 to 11 initially enrolled 2,268 children, and then later enrolled an additional 2,379 children. Vaccination was nearly 91% effective in preventing COVID-19 infection among children ages 5-11 years.

In the original enrollment group of 2,268 children:

• All participants were based in the United States
• Sex distribution:
• 47% female
• 53% male
• Racial/ethnic distribution:
• 79% White
• 21% Hispanic or Latino
• 6% Asian
• 6% Black or African American
• 1% American Indian or Alaska Native
• <1% Native Hawaiian or other Pacific Islander

Pfizer’s clinical trials for those ages 12 to 15 enrolled 2,260 children and youth in the United States. None of the youth who received the vaccine developed COVID-19.

Pfizer Clinical Trial Participant Summary, Children and Youth ages 12-15

• 2,260 enrolled, all based in the United States. 
• Sex distribution: 
• 49% Female 
• 51% Male 
• Racial/ethnic distribution:   
• 86% White 
• 12% Hispanic or Latino 
• 6% Asian 
• 5% Black or African American 
• <1% American Indian or Alaska Native 
• <1 % Native Hawaiian or Pacific Islander, no participants in the Placebo 

The COVID-19 vaccine is free for all Alameda County residents, regardless of their immigration or health insurance status.

Check with your child’s healthcare provider about whether they offer COVID-19 vaccination. Alameda County parents and legal guardians can also schedule appointments for young people in their families 5 years of age and older to receive a COVID-19 vaccine using the statewide and county booking system.

The best place for you to get your 6-month to 4-year-old child vaccinated is their pediatrician’s office. This is an excellent opportunity to obtain a child’s routine vaccinations and learn about other programs and services that can support a child’s healthy start. Children 3 and older can also get their vaccination at some pharmacies.

If you need support signing up your child for health insurance, please contact our Inquiries line at 510-268-2102.

Make an appointment with an Alameda County site: AlCoVax Signup or call 510-208-4VAX. You can also visit Where to Get a Vaccine in Alameda County.

• Been receiving active cancer treatment for tumors or cancers of the blood  

• Received an organ transplant and are taking medicine to suppress the immune system  
• Received a stem cell transplant within the last 2 years or are taking medicine to suppress the immune system  
• Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)  
• Advanced or untreated HIV infection  
• Active treatment with high-dose corticosteroids or other drugs that may suppress your immune response