Today, multinational pharmaceutical company Pfizer reported their mRNA-based vaccine candidate, BNT162b2, was more than 90 percent effective against SARS-CoV-2, based on early phase 3 clinical trial data.

The study enrolled 43,538 participants in six countries who were spilt into two groups: a group that was received the vaccine candidate, and a group that received a placebo treatment.

Since the start of the phase 3 trial on July 27th, 94 confirmed cases of COVID-19 have been reported in the study group. Fewer than 10 percent of those cases were from participants who had been given the vaccine candidate, and more than 90 percent of the cases were from the placebo group.

Pfizer reported no serious safety concerns with the vaccine, and that 42 percent of the trial participants had racially or ethnically diverse backgrounds. The second point is key, as BIPOC communities show higher rates of COVID-19 infection, hospitalization, and mortality than white, non-Hispanic communities.

The study will continue monitoring their participants until 164 confirmed cases of COVID-19 occur in the trial population to gain more accurate information about the vaccines efficacy.

How does it work?

The vaccine candidate contains genetic material from the virus called messenger RNA. As its name suggests, messenger RNA carries information between different parts of a cell, providing instructions like which proteins to make.

BNT162b2 uses messenger RNA that describes one of the spike proteins that stud the outer surface of SARS-CoV-2. Though human cells dont make spike proteins, they can still read viral messenger RNA and follow its instructions. When someone receives a dose of BNT162b2, their body responds by producing the spike protein, but only the spike protein, and no other part of the virus.

Since spike proteins arent normally found in human cells, their presence triggers the immune system, leading to a defensive response where the proteins are removed. Now that the immune systems had some practice, its ready for the real thing. If someone who was vaccinated against SARS-CoV-2 was exposed to the virus later on, their immune system is ready to react, and hopefully, fend off the virus.

Messenger RNA vaccines are relatively new on the scene, but have the potential to be safer and more effective than other vaccine types. There is no risk of getting COVID-19 from a vaccine, as the virus is never present in the body.

Hold on, there are some caveats

The Pfizer data is promising, but there are some barriers that will need to be dealt with should BNT162b2 see broad production and distribution.

The logistics are tricky, as the drug must be stored in a -80oC (-112 oF) freezer. This is standard equipment for biomedical research labs in universities and hospitals, but rare in doctors offices and pharmacies. This is a severe requirement even by the standards of vaccines. Inactivated flu vaccines can often be stored in a normal 2-8oC fridge, and even Moderna's similar mRNA vaccine only needs to be frozen at -20oC. Moderna's vaccine is also stable longer once thawed (that is to say that Pfizer's vaccine deteriorates faster once unfrozen), which would make administering it to a population a bit easier.

The vaccine also needs two doses. This means at least twice as much vaccine needs to be manufactured as a single dose treatment, assuming perfect compliance with vaccine scheduling. In their press release, Pfizer reported they expect to produce globally up to 50 million vaccine doses in 2020 and up to 1.3 billion doses in 2021.

Another issue with multi-dose vaccines is that not everyone can reliably get both doses, leading to inequality in vaccine access. For example, Black and Hispanic/Latinx adolescent girls are disproportionately prone to low HPV vaccination completion rates compared to white adolescent girls after adjusting for difference in socioeconomic status and insurance coverage. Solving vaccine access and completion issues will be key to high vaccination rates and creating herd immunity to COVID-19.

Though this is still much work to do (including the completion of the clinical trial), this announcement has been hailed as welcome news in the ongoing worldwide health crisis.

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