Vaccine FAQs
What is in the vaccine?
The active ingredient is messenger RNA (mRNA) that carries instructions for making the virus’s spike protein, that the virus uses to gain entry to your cells. The mRNA is synthetic, not extracted from actual viruses. It is delivered in a tiny sphere of inert fatty material called a lipid nanoparticle. The RNA-bearing nanoparticles are mixed in saline solution and injected into muscle tissue in your upper arm. The mRNA is then taken up by special immune cells, which then follow instructions, coded in the mRNA, to make the coronavirus spike protein, just as they would do if they had become infected with the actual virus. The mRNA instruction only produces a small piece of the virus and cannot make a person sick nor can it cause the virus to be manufactured in the person’s body. This mRNA instruction only lasts a short time inside the cell and is subsequently disintegrated by the cell. It does not become part of your genetic code. You cannot pass this on to other people from products of your blood, nor can you pass this on to unborn children.
The COVID19 Spike protein is recognized as foreign by your immune system, which mounts an attack against it. Antibodies, B cells and T cells (long-lasting regulatory parts of your immune system) from your body are activated. Your immune system learns from this how to defeat the virus and is primed to mount a swift response if it encounters the coronavirus again.
How long does protection from the vaccine last?
We don’t know how long protection lasts for those who are vaccinated. What we do know is that COVID-19 has caused very serious illness and death for a lot of people. If you get COVID-19, you also risk giving it to loved ones who may get very sick. Getting a COVID-19 vaccine is a safer choice.
Experts are working to learn more about both natural immunity and vaccine-induced immunity. CDC will keep the public informed as new evidence becomes available.
If I have an underlying condition, can I get the COVID-19 vaccine?
People with underlying medical conditions can receive a COVID-19 vaccine as long as they have not had an immediate or severe allergic reaction to a COVID-19 vaccine or to any of the ingredients in the vaccine. Learn more about vaccination considerations for people with underlying medical conditions. Vaccination is an important consideration for adults of any age with certain underlying medical conditions because they are at increased risk for severe illness from COVID-19.
How long does it take for immunity to develop fully after vaccination?
We know that partial protective immunity builds up within weeks of the first dose and is more complete 4 weeks after the second dose.
It’s a two-shot vaccine, so what happens if people miss their second shot? Is a single shot still protective?
Two shots are needed, and the second shot is required to attain immunity. The gap between doses in the trial ranged between 19 and 42 days. Only 2 percent of people in the trial missed their second dose so it isn’t entirely clear what happens under those circumstances.
Are there any side effects?
Sometimes, but they are mild and last 1-2 days. It is best to think of these as evidence of your immune system responding as expected to the vaccine rather than something bad. In the trial, the vaccine was well-tolerated, and an independent data monitoring committee reported no serious safety concerns. The worst side effects were fatigue and headaches, more common after the second dose. Approximately 26% reported mild fatigue with the first injection and 21% with the second injection.
Approximately 56% of people reported mild injection site pain, 47 percent of people reported mild fatigue and 27 percent a mild headache. These are common reactions you would have with vaccination. Older adults reported fewer and milder side effects.
Warmth, slight swelling and a little bit of firmness are typically seen at the injection site. In the clinical trials, 55% had mild injection site soreness, 3% had mild redness and 4% had mild swelling. These numbers increased slightly with the second dose
Three percent of individuals in the clinical trial developed a fever (temperature greater than 100.4) with the first injection while 16% did on the second injection. Approximately 11% developed mild muscle pains on the first injection while 15% it on the second injection
Does it work in older people?
Yes. Trial participants were aged up to 85, and the efficacy in people over 65 was 94 percent – slightly lower than the overall number but still very protective, and much higher than some vaccine experts thought.
What about other vulnerable groups?
The vaccine appears to be equally effective regardless of recipients’ age, sex and ethnicity. It has been tested extensively in people who have already had the virus and it did not cause any ill effects. It has also been tested in people with “stable” pre-existing conditions – also known as comorbidities – including diabetes, cancer, hepatitis B, hepatitis C and well-managed HIV.
What if I am pregnant or breast-feeding?
Yes, COVID-19 vaccination is recommended for all people 12 years and older, including people who are pregnant, breastfeeding, trying to get pregnant now, or might become pregnant in the future. You might want to have a conversation with your healthcare provider about COVID-19 vaccination. While such a conversation might be helpful, it is not required before vaccination. Learn more about vaccination considerations for people who are pregnant or breastfeeding.
If you are pregnant and have received a COVID-19 vaccine, we encourage you to enroll in v-safe, CDC’s smartphone-based tool that provides personalized health check-ins after vaccination. A v-safe pregnancy registry has been established to gather information on the health of pregnant people who have received a COVID-19 vaccine.
Does this vaccine contain any preservatives or was it made using fetal tissue?
The vaccine does not contain any preservatives, (thimerosal (mercury) for example). No fetal stem cells or human blood products are involved in its production.
I have recovered from COVID19 infection earlier this year, should I receive the vaccine now?
Yes, you should receive the vaccine. Individuals with previous infection received the vaccine in the clinical trials without appreciable adverse effect. The duration of protection from natural infection is not known and vaccination may extend your degree and duration of protection.
Can I get vaccinated while I'm currently sick with COVID-19?
No. People with COVID-19 who have symptoms should wait to be vaccinated until they have recovered from their illness and have met the criteria for discontinuing isolation; those without symptoms should also wait until they meet the criteria before getting vaccinated. This guidance also applies to people who get COVID-19 before getting their second dose of vaccine.
