My Patients Ask — How does Johnson & Johnson’s COVID-19 vaccine compare to Moderna, Pfizer?

With Johnson & Johnson’s COVID-19 vaccine facing an FDA- and CDC-recommended pause after several instances of severe blood clots were reported in recipients, those scheduled to receive J&J shots may find themselves having to find an alternative. How does the Moderna or Pfizer vaccine compare?

According to the FDA and CDC, as of today, there have been six reported cases (including one death and one hospitalization) of a rare and severe type of blood clot in over 6.8 million Johnson & Johnson COVID-19 vaccine recipients.

That means the absolute risk appears to be less than one in a million. If you’ve had the J&J  vaccine, I blogged earlier this week on what to be on the lookout for.

Fox News has a nice article on how the Moderna and Pfizer shots compare.

Vaccines developed by Moderna and Pfizer-BioNTech operate on a newer platform with mRNA, or messenger RNA, technology.

The Johnson & Johnson’s candidate involves a more traditional modified adenovirus vector vaccine with a durable protein exterior encasing the DNA, lending itself to a longer shelf-life. The AstraZeneca vaccine uses the same technology. It was approved for use in Europe, but not yet in the U.S.

Clinical trials indicated vaccines developed by Pfizer and Moderna were about 95% effective against symptomatic illness, and Johnson & Johnson’s candidate had a 66.3% efficacy.

However, the trial data also revealed ALL three vaccines were highly effective in preventing hospitalizations and deaths.

It’s also important to note that Pfizer and Moderna’s vaccines each require a two-dose regimen while, Johnson & Johnson’s product requires just a single dose, which eased logistics prior to the national pause.


While the Pfizer and Moderna COVID-19 vaccines train the body to recognize the spike protein that coats the outer surface of the coronavirus, the J&J and AstraZeneca vaccines use a cold virus, called an adenovirus, to carry the spike gene into the body.

J&J uses a human adenovirus to create its vaccine while AstraZeneca uses a chimpanzee version. The AstraZeneca vaccine is not yet authorized for use in the U.S.

The J&J and AstraZeneca vaccines are considered “ethically problematic” by some (including me) as they may have used tissue cultures originally derived from the cells of an aborted fetus. (See my blog: Is the J&J Vaccine Ethical?)

A possible cause behind the clotting that occurred among vaccine recipients might be a similar mechanism seen with AstraZeneca’s product, another adenoviral vector vaccine being rolled out in Europe, in which a rare immune response occurred post-vaccination, leading to activation of platelets and “extremely rare” blood clots.


Johnson & Johnson’s vaccine candidate is stable for up to two years at -20 degrees Celsius and at least three months at 2 to 8 degrees Celsius. Moderna’s vaccine can last at -20 degrees Celsius for six months and 2 to 8 degrees Celsius for 30 days.

Meanwhile, in February the FDA eased permitted shipping and two-week storage temperatures for the Pfizer vaccine to -25 degrees Celsius to -15 degrees Celsius in a significant shift from an ultra-cold temperature requirement of -80 degrees Celsius and -60 degrees Celsius for up to six months.

This blog was accurate as of the day of posting. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus and the COVID vaccine develops, the information above may have changed since it was last updated. While I aim to keep all of my blogs on COVID and the COVID vaccine up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news.

© Copyright WLL, INC. 2021. This blog provides a wide variety of general health information only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment from your regular physician. If you are concerned about your health, take what you learn from this blog and meet with your personal doctor to discuss your concerns.


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