Moderna vs Pfizer vaccine: what are the major differences between these vaccine candidates and what do we know so far?

Moderna recently announced that their mRNA vaccine candidate was 94.5% effective in preventing Covid-19, according to an analysis of a clinical trial involving 30,000 patients. This announcement came only a week after Pfizer and BioNTech revealed that their Covid-19 vaccine, which was also created using mRNA technology, was more than 90% effective in a clinical trial of 60,000 patients. So, what are the major differences between these vaccines?

As of now, the efficacy of the vaccines appears to be similar, which is unsurprising given that the vaccines are both based on the same kind of technology (mRNA vaccines). The Moderna vaccine appears to be protective in important subsets of the population, including the elderly and people from communities of color. In the clinical trial, there were only 11 cases of severe disease, all occurring in the placebo group. While the clinical trial conducted by Pfizer and BioNTech included the same subpopulations of participants, they have not yet released any specific results.

In terms of safety, both vaccines are generally tolerable, with only a few short-lived side effects observed in the trial for Moderna, including fatigue, muscle pain, and headache. Pfizer showed no serious safety concerns, aside from mild or moderate fever and pain at the site of injection which resolved over time.

However, it is not yet known how effective these vaccines are in the long-term, or what the "durability of protection will be," according to Anthony Fauci. Further, the trials primarily look at the impact on symptomatic Covid-19, but it is also important to know if the vaccines can block infections entirely. 

All of the current top vaccine candidates are targeting the virus' spike protein which the pathogen uses to infect cells, so "today's announcement provides further confirmation that spike-directed vaccines can provide a protective immune response," according to Richard Hatchett, CEO of the Coalition for Epidemic Preparedness Innovations.

Further, the success of Moderna and Pfizer's vaccines is a massive affirmation of the promise of mRNA vaccines, a technology that has has "advanced in fits and starts for three decades." The fact that two companies have been able to develop an effective vaccine for SARS-2 within less than a year of SARS-2 hitting suggests that mRNA technology can be employed to rapidly design and deploy vaccines for other pathogens in the future. This is very encouraging for Moderna as it continues to develop vaccines for Zika virus and cytomegalovirus and yearly fly vaccines, as well as for BioNTech which is in the process of developing vaccines for cancer, HIV, and influenza. 

Both Moderna and Pfizer plan to file emergency use authorization and if the FDA grants them, as it is expected to by the end of the year, the companies will send the doses to the federal government which will then allocate the supplies to frontline workers and those at higher risk of sever Covid-19. For the rest of the population, neither vaccine is likely to be available until Spring at the earliest, largely due to logistics. The companies are expected to make 70 million doses by the end of 2020, which is enough for only 35 million individuals. Another issue is that of storage and transportation; Pfizer vaccines must be shipped and stored at very cold temperatures, which makes it difficult to transport in parts of the world lacking special freezers, but Moderna vaccines can safely be stored in a normal refrigerator. 

- Claire Hillier

Reference:

Adam Feuerstein, et al. “On Covid-19, Two Vaccines Offer More Answers about the Road Ahead.” STAT, 16 Nov. 2020, www.statnews.com/2020/11/16/with-strong-data-on-two-covid-19-vaccines-we-have-more-answers-about-the-road-ahead-and-questions-too/.