The Differences Between the COVID-19 Vaccines

By: Gordon Chan

Introduction

Last month, the FDA authorized an Emergency Use Authorization for the Johnson & Johnson’s single-dose coronavirus vaccine. The decision, which the FDA announced through a press release, allows the company to distribute the vaccine in the U.S. for use in individuals 18 years and older. Johnson & Johnson (J&J) has already shipped 4 million doses to the U.S. following the vaccine’s new authorization, with an additional 16 million doses to be available by the end of March. With three authorized vaccines in its arsenal, the U.S. aims to distribute 500 million doses by the end of May, which should be enough for every adult. 

Developed by J&J’s vaccine division, Jansen pharmaceuticals, the vaccine was shown to be 66% effective at preventing moderate to severe COVID-19 symptoms. The first two U.S.authorized vaccines, Pfizer and Moderna, are 95% and 94.1% effective at preventing symptomatic infections. At a first glance, the J&J vaccine doesn’t appear to be as effective as the Pfizer and Moderna vaccine, but it does have other advantages over its competition. 

How they work

The Pfizer and Moderna vaccines use messenger RNA, or mRNA, to deliver instructions for your cells to make a ‘spike’ protein, which is found on the surface of the SARS-CoV-2 virus that causes COVID-19. The spike proteins made with mRNA instructions trigger an immune response inside our bodies, which prompts our body to produce antibodies that protect against future infection. 

The J&J vaccine does not use mRNA. Instead, it uses an adenovirus to deliver instructions for your cells to make the spike protein. The adenovirus uses a virus we know is harmless to act as a Trojan horse. But instead of hiding Greek soldiers, the adenovirus releases genes for the spike protein. When the adenovirus gets into your cells, the cell’s DNA is turned into mRNA, causing the cells to make the protein which triggers your body’s immune response. This approach is not new. J&J used a similar method to make its Ebola vaccine, which was authorized for use by the European Union last July. 

Vaccine Efficacy 

The overall efficacy of the Pfizer and Moderna vaccine is higher than the J&J vaccine. The Pfizer vaccine is 95% effective at preventing symptomatic infection after two doses. The Moderna vaccine is 94.1% effective at preventing symptomatic infection after two doses. By contrast, the J&J vaccine is 66% effective at preventing moderate to severe infections. 

It’s important to recognize that the Pfizer and Moderna clinical trials were done over the summer and fall of 2020, before newer more contagious variants emerged. A new study published in the New England Journal of Medicine reports that the Pfizer vaccine was not as effective at preventing symptomatic infections against the coronavirus variant that first appeared in South Africa. The same could apply for the Moderna vaccine as well. The J&J trials were done more recently and include data against these new variants. 

The difference in the trials make direct comparisons a bit unfair, like comparing apples to oranges. The way the vaccines calculate cases of infection is also different. Pfizer started counting cases 7 days after the application of the second dose whereas Moderna waited until the 14 days after the second dose to start counting. J&J assessed vaccine efficacy beginning 14 days after vaccination. 

Number of doses 

Both the Pfizer and Moderna vaccines require two shots, a priming dose followed by a booster shot. The Pfizer vaccine requires 30 micrograms of vaccine for each dose whereas the Moderna vaccine requires 100 micrograms for each dose. So while the Moderna vaccine uses 3 times as much vaccine per person as the Pfizer vaccine, the results are not significantly different. The interval between shots for the Pfizer vaccine is 21 days, whereas the Moderna vaccine interval is 28 days. 

On the other hand, the J&J vaccine is a single-dose vaccine. It does not require a booster shot like the Pfizer and Moderna vaccine. However, J&J is conducting a two-dose trial with 30,000 individuals where the shots are administered eight weeks apart. The results of the trial are expected sometime in May. 

Storage requirements 

The Pfizer vaccine needs to be shipped in thermal containers with dry ice and kept at -70 °C, which is colder than winter in Antarctica. The Pfizer vaccine has a shelf life of five days once it’s removed from it’s cold storage (-70 °C) and stored at normal refrigeration temperatures (2-8 °C). The Moderna vaccine is a bit less extreme, only requiring to be shipped in normal freezer temperatures at -20 °C. The Moderna vaccine can be stored at regular refrigeration temperatures and remain effective for up to 30 days.

The mRNA vaccines require an elaborate cold chain distribution system for shipping and storage, which could slow the rollout of new vaccines in rural U.S. The J&J vaccine does not require such stringent handling and storage conditions. It can be kept at normal refrigeration temperatures (2-8 °C) for up to 30 days, which makes distribution to clinics and rural hospitals much easier. 

Regardless of which vaccine you have access to, it is highly recommend that those who are eligible get vaccinated as soon as possible. Doing so will help us move our lives back to normal as quickly as possible.