Bloom's Health and Safety Q&A:
Your COVID-19 Vaccine Concerns Answered

Authors: Sima Sobhiyeh, Ph.D.; Alexander Stemer, M.D. Infectious disease; Joe Kurland, M.P.H., C.I.C.; Leah Shaffer, Ph.D.; Sarah Ali, M.P.H.; Yasmin Saidi

Bloom Advisory strongly advises people to get vaccinated as it is a critical step to our way out of the pandemic. 

Up to 3 million lives are saved by vaccines worldwide per year, and thanks to past vaccine roll-outs, diseases like smallpox, polio, and diphtheria no longer exist or are very rare. If enough people are vaccinated, pathogens are prevented from spreading to people who can’t have vaccines. For example, people who are ill or have a weakened immune system. This is called “herd immunity.”

How do COVID-19 vaccines work?

They work the same way all vaccines do by triggering our immune system to produce antibodies that can prevent the virus from entering our cells, stopping the infection. 

Our team of experts has compiled answers to common questions and concerns about the COVID-19 vaccines:

If an ill family member is hospitalized, will my COVID-19 vaccination affect them in any way?

No, getting the vaccine will protect you, allow you to care for your family member, and may even reduce the chance that you could unknowingly spread the virus to them if you were exposed to COVID-19 somewhere. Recent studies show that vaccinated people are much less likely to spread the virus. The vaccine does not cause COVID-19, it gives protection against it.

Do the vaccines cause infertility?

No, the vaccine does not cause infertility, nor does it cause issues with the placenta. Pregnant and breastfeeding women can get the vaccine. Many OB-GYN clinicians may advise expecting moms to get vaccinated as infection with the virus poses an increased risk for pregnant women. As additional fertility evidence, a recent study published by the New England Journal of Medicine reported vaccinated women have become pregnant after COVID-19 vaccination. 

Do the vaccines give you COVID-19?

None of the vaccines contain live viruses and cannot cause COVID-19 infections. The vaccines provide the immune system either the proteins or the blueprints to build proteins on the surface of the SARS-CoV-2 virus. Your immune system uses these proteins as target practice to better recognize and fight the real virus if and when it appears.

Do these vaccines alter your DNA?

No. The Pfizer BioNTech and Moderna vaccines use mRNA or messenger RNA, which is very different from DNA. The vaccines cannot change or edit your DNA. mRNA cannot enter the portion of your cell that holds DNA. Your DNA is in the middle of the cell (in the nucleus), whereas the mRNA vaccines do their work in the part of the cell outside of the nucleus. The mRNA does not enter the cell’s nucleus, so it cannot alter your DNA.

In our cells, mRNAs act like recipes, telling the cell how to make all the different protein molecules that are essential for our cells and organs to work. In the case of these vaccines, the mRNA instructs your cells to make the COVID-19’s spike protein only. It does not have the information to make the whole virus. Your body then produces an immune response by creating antibodies to fight the virus protein. This makes your immune system ready to fight the real virus if it enters your body. 

The Oxford/ AstraZeneca and Janssen (J&J) vaccines don’t use mRNA – instead, they use a weakened virus, called adenovirus, to deliver genetic instructions to your cells. The adenovirus vaccines use genetic codes to produce a spike protein in the body, and like the mRNA vaccines, this code is not incorporated into your genetic material. The adenovirus is weakened and isn’t able to replicate within your body, and it cannot alter or edit your DNA.  After the genetic instructions in mRNA and adenovirus vaccines have been delivered to your cells, they are broken down by your cells and disappear from your body within a few days.

We do not know what is in these vaccines. Do they contain animal fat?

No. The Pfizer-BioNTech and Oxford-AstraZeneca vaccines do not contain human or animal-derived ingredients. Pfizer and Moderna vaccines DO NOT contain human cells (no fetal cells, blood products, or human material), other animal cells, any virus, preservatives, shellfish, common food allergens, or latex. They do not contain microchips.

Specifically, the Pfizer vaccine contains: Messenger RNA (aka mRNA): A molecule made in a lab out of smaller molecules, A blend of four different fat molecules, Four different types of salts, which combine to form phosphate-buffered saline (PBS), a very common drug ingredient that stabilizes the acidity of the mixture, Sugar.

The Moderna vaccine contains: Messenger RNA (aka mRNA). A molecule made in a lab out of smaller molecules, A slightly different blend of four different fat molecules: Four ingredients that stabilize the acidity of the mixture: acetic acid, two different acid stabilizers, and a salt, Sugar.

In both cases, this ingredient list has been reviewed by the FDA and is printed on the vaccine package inserts.

I have already had COVID-19, so the vaccine will not benefit me. True or false?

COVID-19 is a virus. Just like any other virus (e.g., flu), it can mutate and replicate and infect again. Therefore, taking the vaccine will benefit you even if you have already had COVID-19 before. There is increasing evidence to show that, unlike vaccination, natural infection with COVID-19 does not lead to long-lasting immunity.

These vaccines have been developed so quickly; how do I know that they have been tested properly?

The COVID-19 pandemic led to an international effort in vaccine development. The urgent need to control the pandemic, and save lives, meant that development processes were significantly accelerated. This does not mean that steps were skipped or that safety was compromised. The science behind these vaccines has been in development for several decades. Since the 2003 SARS-1 outbreak, scientists have been working to develop vaccines against Coronaviruses. It was a quick and (relatively) easy change to make the vaccines under development target SARS-CoV-2 rather than the SARS virus that struck in 2003. Vaccine production is a balance between cost, safety and efficacy, and speed.  The US government spent $10 billion to allow the vaccine companies to focus on how well the vaccines would work and how quickly they could be mass-produced.  These funds came from our tax dollars.  We’ve already paid for the vaccines; let’s use them!


  1. Pardi et. al., mRNA vaccines – a new era in vaccinology, Nature Reviews Drug Discovery, vol. 17, pp. 261–279, 4/2018. 
  2. Shimabukuro et. al., Preliminary Findings of mRNA COVID-19 Vaccine Safety in Pregnant Persons, New England Journal of Medicine, 04/21/2021. 
  3. Shah et al., Effect of vaccination on transmission of COVID-19: an observational study in healthcare workers and their households, BMJ Yale – MedRxiv, 04/21/2021 (pre-print).
  4. Levine-Tiefenbrun, et. al., Decreased SARS-CoV-2 viral load following vaccination, BMJ Yale – MedRxiv, 02/08/2021(pre-print).
  5. FAQs about COVID-19 Vaccines, Vaccine Knowledge Project, Univ of Oxford, 03/17/2021.
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