Yes, Bonnie, the Covid vaccine is safe.

Moderna’s mRNA vaccine for Covid-19. [Image credit: AP/Paul Sancya]

An open letter to my niece.

Dear Bonnie,

This is the summary of my thoughts on the Covid-19 vaccines that you recently requested. You told me I had helped you change your mind about getting the vaccine when we discussed it on the phone, and you said you wanted to share my thoughts with others who might be reluctant to get vaccinated.

I’ll start by introducing myself to any readers who know nothing about me. I’m Bonnie’s uncle, which is part of the reason she trusts me, but she also appreciates that I know a lot about biology. I’m retired now but spent most of my adult life in science. I have a bachelor’s degree in biology from Caltech and a PhD in neuroscience from UC San Diego. I’m also a computer nerd, and most of my work has involved using computers to try to solve interesting puzzles in biology. I am not a specialist in any of the fields most relevant to the issues of vaccine safety and efficacy:  virology, immunology, or epidemiology. I am not a medical doctor. But I know how science works and I know enough about molecular biology and clinical trials to evaluate recent news reports about the success of the Covid-19 vaccines.  I’m also qualified to assess the many rumors and conspiracy theories about them. I will try to address the most common reasons given for vaccine reluctance, starting with the main one that Bonnie was worried about:

Objection 1: This vaccine is a rush job, so how can I trust it?

A few weeks ago, Bonnie told me she was afraid of getting either of the new vaccines (from Pfizer and Moderna) because they had been developed so quickly (less than a year). She correctly pointed out that vaccine development normally takes several years, so how could she trust the product of a rush job?

I explained that there are three good reasons that these vaccines could be developed so quickly, without taking any dangerous shortcuts:

  1. Genome sequencing is now cheap, easy, and fast. Chinese scientists were able to determine the complete sequence of the SARS-CoV-2 viral RNA genome within a matter of days. They published the sequence online on January 10, 2020. Scientists all over the world could then know the complete molecular structure of this virus and start developing vaccines to attack it.
  2. Thirty years of research went into the SARS-CoV-2 vaccines, but that all happened before the pandemic. To understand how that is possible, you need to understand how mRNA vaccines work. Both the Pfizer/BioNTech and Moderna vaccines are based on a new approach that uses synthetic messenger RNA (mRNA) to generate an immune response. Messenger RNA is a temporary “working copy” of a gene that a cell uses to make a protein molecule. All living cells do this all the time; it is a completely natural process essential to life. The mRNA vaccine uses a synthetic mRNA (made by a machine) that contains the instructions for making the spike protein that covers the surface of the SARS-CoV-2 virus particle. When the vaccine is injected into a person, the mRNA enters that person’s cells, which then read the instructions and start producing the viral spike proteins.  The immune system detects these and generates an immune response to attack them.  There were many technical problems that had to be overcome to make mRNA vaccines work. Thirty years of research went into their development. Those problems had all been solved before the pandemic began in 2019. All that was needed was to plug in the sequence of the viral protein. When the genetic sequence of the spike protein was published by the Chinese in January of 2020, an mRNA vaccine could be (and was) synthesized within a matter of days. A mere 42 days after the sequence was published, Moderna sent its first batch of several hundred vials to the National Institutes of Health for preliminary trials. Full-scale clinical trials, involving tens of thousands of subjects, would take months, but the results were stunning: more than 90% efficacy.
  3. Phase 3 clinical trials run faster if the disease is out of control, and that was the case with Covid-19 in America in 2020. Partly because of widespread Covid denial and refusal to wear masks and practice social distancing, and also because of inadequate testing and contact tracing, the pandemic exploded across our country last year. Remember spring of 2020, when we thought 125,000 Americans might die before it was over? Now we know the final body count will be at least quadruple that. Ironically, however, our botched response to the pandemic accelerated vaccine development. To prove safety and efficacy of a vaccine, we enroll tens of thousands of patients and randomize them into two groups. One group gets the vaccine and the other group gets a placebo. We wait until a significant number of subjects get infected and then look to see how many of those infections were in the vaccine group compared to the placebo group. Typically it takes a year or two for enough people to get infected that you can make this comparison. By the time the phase 3 trials started for the Covid vaccine, the virus was so far out of control that within a mere two months there were enough infections to prove that the vaccine worked extremely well at preventing disease.

Objection 2: I’m from a racial minority. Why should I trust a medical establishment that used black men as guinea pigs for a study of syphilis?

The Infamous Tuskegee Study

America has a history of slavery and racism, and the Tuskegee study of syphilis, from 1932 to 1972, is part of that shameful past. So are less egregious but more pervasive sins, like implicit bias in physicians when evaluating the symptoms of minority patients or the underrepresentation of minorities in clinical trials. Like the rest of American society, the scientific and medical communities are evolving and trying to right their past wrongs. There are now strict laws and regulations demanding informed consent in any scientific study of human subjects; medical students are being taught about implicit bias; and outreach programs have increased the representation of minority groups in clinical trials.

But if you’re worried about racial disparities and Covid, vaccine safety is not where you should focus your attention. The real problem is that minorities are significantly more likely than whites to catch Covid-19 and, once infected, more likely to die from it. This makes the need for vaccination especially urgent for minorities.

Objection 3: I’m worried that the vaccine might cause Covid-19 disease.

No, it won’t. This is a legitimate concern for vaccines derived from whole virus particles, either weakened or killed. Polio vaccines were made this way, and if the procedures for weakening or killing the virus were not properly followed during manufacture, a small fraction of people getting the vaccine could and did get polio.

This is not a problem with either of the two approved mRNA vaccines for SARS-CoV-2. The only piece of the virus introduced into the body by the vaccine is the spike protein, which is harmless by itself.  Because the other 26 proteins of the virus are missing, the vaccine cannot cause Covid-19 disease.

As I’m writing this, data from clinical trials of the Johnson & Johnson vaccine have just been announced, and it will likely be approved soon. This is a whole virus vaccine, but the virus used is not the one that causes Covid-19.  Instead it is a harmless virus that has been modified to produce the spike protein from SARS-CoV-2. As with the mRNA vaccines, the only piece of the deadly virus is the spike protein, which is harmless by itself, so the Johnson & Johnson vaccine cannot cause Covid-19.

Having said all that, I hasten to add that you will probably feel weak and feverish for a day or two after getting any of the Covid-19 vaccines.  Those are merely symptoms of the immune response your body is mounting to attack the alien spike protein.

Objection 4: I heard the vaccine will alter my DNA.

This is false. Messenger RNA is a temporary working copy of a gene, not the gene itself. If you have a copy of the Declaration of Independence and use white-out and a pen to change “all men are created equal” to “all people are created equal”, it will not in any way affect the original document housed in the National Archives. So it is with the mRNA vaccines and your own DNA. There are some viruses (not vaccines) that are capable of incorporating their genes into your DNA, and confusion about this fact may be the source of this rumor. Although SARS-CoV-2 is not one of those viruses, there is evidence that fragments of the SARS-CoV-2 genome can be integrated into the genome of infected patients. So if you don’t want Covid genes incorporated into your DNA, your best strategy is to avoid getting infected, and the best way to do that is to get vaccinated.

Objection 5: I heard there have been severe allergic reactions to the Covid vaccines.

This is true, and if you have a history of severe allergic reactions to anything – especially to some other kind of vaccine – then you should discuss this with your doctor before getting the vaccine. Allergic reactions to the mRNA vaccines are rare, and to my knowledge no one has yet died from this, but some people with severe allergies are being advised not to get the vaccine. If you are one of them, then you must depend on masks, social distancing, and the vaccination of everyone around you to keep you safe. And that brings us to…

Objection 6: I won’t take the vaccine because I believe that Covid is a hoax, or that it’s not as bad as everyone says, or that the vaccine is more dangerous than the disease. It’s my life and I’ll take the risk.

Anti-lockdown protesters in PA, May 2020 [Image credit: AFP/Nicholas Kamm]
The problem with this is that your refusal to take the vaccine doesn’t only affect you. It affects others around you who may not be able to take the vaccine, either for medical reasons (see Objection 5) or because of scarcity of the vaccine. Even if you are one the many people who catch Covid and never have severe symptoms, you can easily spread it to others who will get sick and possibly die. Also, by refusing the vaccine, you are offering your body as fertile ground in which the virus can replicate, mutate, and evolve into ever more dangerous strains. We know that the Covid vaccines are highly effective at preventing disease. We don’t yet know that vaccinated subjects are less likely to spread the virus, though this seems likely. The pandemic will stop only when the virus runs out of people to infect, and masking, social distancing, and mass vaccination are the only safe ways to make that happen.

There are other objections that I will not discuss here. Instead, I recommend this commentary from the Mayo Clinic.

Update, February 9, 2021: Immune thrombocytopenia: Yesterday the New York Times reported that a small number of cases of a serious autoimmune disorder, immune thrombocytopenia, may be linked to the Moderna and Pfizer vaccines for Covid-19. In patients with this condition, the immune system attacks and destroys platelets in the blood. The disease is treatable, but in severe cases the risk of hemorrhage is life-threatening. The article specifically describes two cases and mentions that 36 similar ones have been reported among the more than 31 million recipients of the mRNA vaccines. It is not yet known whether these cases are caused or triggered in some way by the vaccine, though one expert quoted in the article said it is possible. Typically there are about 50,000 people in America who have this autoimmune disease, which sometimes appears following a severe viral infection. Even if the few dozen cases so far reported turn out to be caused by the Covid vaccine, the roughly one-in-a-million risk of getting thrombocytopenia is negligible compared to the risk of death from Covid-19. You can read the full article here.

Finally, science is not a conspiracy, and scientists are not out to get you. Science is the most effective means humans have yet devised for discovering the truth about how reality works. The proof of that statement is all around you: your computer, your smartphone, your car, your prescription drugs, your reliable food supply, and your extended life expectancy. Scientists can do a lot to save lives and end the Covid-19 pandemic, but they can’t do it alone. They need your help and cooperation. Wear a mask, practice social distancing, and get vaccinated as soon as you can.


Special thanks to my dear friend Meg Marshall (a physician and immunologist) who read an early draft of this and suggested significant improvements.

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Posted January 31, 2021; Filed under: Nature Tags: , , , , , , , ,

11 Comments on “Yes, Bonnie, the Covid vaccine is safe.

  1. Uncle Jack,
    Thank you so much for composing all of this information and sharing your wisdom! I will encourage as many people as I possibly can to get vaccinated! ❤

  2. Thank you Bonnie for sharing this information. It has definitely put some of my thoughts and concerns at ease!

    Sharon B

  3. Thank you so much. I got vaccinated last week due to my PCP signing me up at the Gastonia Hospital and I was concerned but I am a caregiver for a 85 year old with many health problems. I certainly don’t want to get him infected due to my lack of trying to do the best I can not to get infected. This was very helpful.

  4. Thank you so much for this information. The simple explanations to the questions that I had asked is comforting. Please keep us informed! Bonnie, I absolutely love you!

  5. Thank you Bonnie for sharing this information with us. It touched on every concern I had about getting vaccinated.

  6. Thank you Bonnie for sharing this information
    From your uncle and thank him as well for
    Taking his time, expertise, and resources to
    Address some of the concerns a lot of us have.

  7. Here’s a an update: My wife and I each got our first dose of the Moderna vaccine two days after I posted this article. We had a little soreness at the injection site for about a day after that, but since then no problems at all. We’re looking forward to getting dose number 2 in early March. I recently read that the symptoms of fever and muscle aches are more common after the second dose than after the first.

  8. Another update: My wife and I got our second doses in mid-March and are now as immune as we can be. We are enjoying the freedom to shop, travel, and see friends in person without fear of infecting others or getting infected ourselves. Life is still not completely back to normal, of course, because most people have not yet been vaccinated and new, more virulent strains of SARS-CoV-2 are emerging and spreading rapidly. In Europe, hospitals are again being overwhelmed in some areas and new lockdowns are being imposed. The same could easily happen in America in the coming months, so I urge all of my friends to get vaccinated as soon as possible and follow other public health guidelines. For me, one of the most satisfying aspects of my newly acquired immunity is the knowledge that I am part of the solution, not part of the problem. Please do your part and share that feeling.

    For more on the situation in Europe:

  9. Hi Uncle Jack!
    Many of my coworkers and I have been “fully vaccinated” since the first week of April! Our Mecklenburg County Clerk of Court, the Honorable Elisa Chinn-Gary arranged for the County to vaccinate us on site at work. Thank you again for sharing the abundance of facts, as well as your knowledge and wisdom! So glad to hear you and aunt Maryann are doing well and enjoying life!
    Love you guys!

    1. Dear Bonnie,

      I’m delighted that you and your coworkers are vaccinated. You can all take pride in being part of the solution. You are helping us avoid the fate that has befallen poor India now. I hope our nation can help them.

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