If ever there were a noble new year’s resolution for 2021, successfully defeating the COVID-19 disease would have been it. Unfortunately, complete eradication of this global virus is not looking likely as the World Health Organization’s definition of disease eradication applies only if it can be eliminated everywhere. However, thanks to vaccine production, we may be able to control COVID-19 and its variants, and perhaps get a semblance of our normal lives back.

There are currently three major COVID-19 vaccines in play – those developed by:

  • Pfizer-BioNTech
  • Moderna
  • Johnson & Johnson (J&J)

At the time of writing, over 42 million COVID-19 vaccination doses have been administered throughout the US. None of these vaccines is technically FDA-approved; however, both the Pfizer and Moderna drugs have been granted emergency use authorization (EUA), Pfizer on Dec 11th 2020 and Moderna one week later. Johnson & Johnson released results of its vaccine in early February indicating that it was 85% effective in preventing severe illness from COVID infections. As a result, it has submitted a request for EUA to the FDA.

Emergency Use Authorization is granted by the FDA for unapproved medical products to diagnose, treat, or prevent life-threatening diseases when there are no other adequate, approved, and available alternatives.

With memorable names like BNT162b2 (Pfizer’s vaccine), mRNA-1273 (Moderna), and JNJ-78436735 (J&J), all the information about the COVID immunization scene can be a little overwhelming. Here’s a summary of the interesting bits.

How the COVID vaccines work

Both the Pfizer and Moderna vaccines are based on a piece of single-stranded genetic material known as messenger RNA, or mRNA. The mRNA instructs the body’s cells to produce a spike protein on the surface of the cell. This spike protein is a harmless replica of the same surface proteins found on the SARS-CoV-2 virus, the virus behind COVID-19. By presenting this foreign protein throughout the body, the body’s immune system is then triggered to build an immune response against the real virus but without the life-threatening effects of an actual COVID-19 infection.

Conversely, the J&J vaccine employs the use of double-stranded DNA to induce human cells to produce the SARS-CoV-2 spike protein. This is known as a viral vectored vaccine, using a modified existing virus, in this case, an adenovirus, engineered to contain the DNA needed to make the SARS-CoV-2 surface protein. Adenoviruses are a common family of viruses, often responsible for the common cold. When used in a viral vectored vaccine, the virus is altered in such a way that it can enter our body’s cells (necessary for the production of the spike proteins) but it cannot replicate itself and cause an illness.

Similar to the Pfizer and Moderna mRNA drugs, the presentation of this SARS-CoV-2 spike protein then activates the body’s immune system to produce the appropriate antibodies at the ready should one be unfortunate enough to encounter the real SARS-CoV-2 virus.

Administration and dosage

All three vaccinations are administered via intramuscular injection into the upper arm. Both Pfizer and Moderna vaccines require two shots, Pfizer’s given 3 weeks apart and Moderna’s 4 weeks apart. A big plus of J&J’s developing drug is that it only requires one sting in the arm but the company is also testing the outcome of a two-shot series with 8 weeks in between; these results are expected to be revealed closer to mid-year 2021.


The efficacy of a vaccine is tied to its performance at reducing the incidence of disease under defined and controlled circumstances. While being mindful that this may not necessarily translate to real-world vaccine effectiveness, the trials conducted in the development of all three vaccines yielded promising results.

Pfizer’s drug demonstrated 95% efficacy at preventing COVID-19 in people without previous infection during clinical trials after two doses of the vaccine while Moderna’s offering was 94.1% effective after completing the two-shot series. The clinical trials for both companies included participants across a range of ethnicities, ages, both males and females, and also included some people with pre-existing medical conditions. However, it should be noted that “efficacy” criteria between the companies’ clinical trials were not the same. While both determined efficacy based on the number of symptomatic cases, Pfizer began noting these cases one week following the second dose while Moderna began noting cases 2 weeks following their second dose.

Johnson & Johnson determined efficacy based on the number of moderate-to-severe COVID cases (defined as a positive COVID test result and at least one symptom). Numbers were counted at both 14 days and 28 days after the shot was given. After 28 days, the vaccine was found to be 66% effective. This sounds low, but remember the criteria was specifically moderate-to-severe disease, and more optimistically, after day 49 of the vaccination, efficacy was 100% at preventing severe illness. When calculating based on geographic location, J&J’s vaccine was found to be 72% overall effective in the US.

Safety and side-effect profiles

When it comes to any medication, safety tends to be near the top of the list of public concerns (along with whether the medication actually works or not). When it comes to side effects, most, if not all, vaccines are associated with some sort of adverse reaction. Many of these effects are a result of the vaccine doing what it’s supposed to do – jumpstart your immune system. The most common side effects associated with COVID vaccines are pain, swelling, and redness at the injection site, and chills, tiredness, and headache throughout the body. These reactions are more common with the second dose and typically fade away in a few days after receiving the vaccine.

More severe allergic reactions to Pfizer and Moderna vaccines, known as anaphylactic reactions, have been reported. If not treated promptly, anaphylaxis can be life-threatening. Although a longer period of time is required to really ascertain the risk of anaphylaxis, existing data suggests the risk of the vaccine causing anaphylaxis is around 6.2 cases per million doses (Pfizer) and 2.1 cases per million (Moderna). J&J’s drug has not yet reported any anaphylactic reactions.

Safety and side effect feedback is not available for pregnant and breastfeeding women because this demographic was not included in the clinical trials.

Storage and distribution

In addition to the advantage of only needing to be injected once, J&J’s vaccine offers another big plus when it comes to storage and transport. Pfizer and Moderna mRNA drugs both require cold chain transportation, with the Moderna vaccine needing to be kept under -4 degrees Fahrenheit and the Pfizer drug requiring a very chilly -94 degrees Fahrenheit to remain viable. J&J’s vaccine, on the other hand, is happy in a regular freezer, and can be quite content there for at least 3 months. Pfizer’s vaccine must be used within 5 days of emerging from the ice while Moderna’s is stable at fridge temperature for only 30 days. The high maintenance requirements of the mRNA vaccines limit its distribution and administration in locations that cannot meet these cold chain demands while J&J’s more robust double-stranded DNA drug makes it much more convenient to get around.

Long-term view

At the moment, there has simply not been enough time to determine 1) the length of time these vaccines will protect us from SARS-CoV-2, 2) their long-term safety, and 3) whether we will need ongoing booster shots to maintain protection. While vaccinations continue to be rolled out around the world, please continue to practice simple hygiene measures such as thorough 20-second, lathered handwashing, wearing appropriate face masks, and social distancing.