Pfizer announces coronavirus vaccine that is over 90% effective, here’s all you need to know about it

Questions such as how long the protection may last, whether it protects those who have previously had the infection and whether it stops virus transmission, remain unanswered

                            Pfizer announces coronavirus vaccine that is over 90% effective, here’s all you need to know about it
(Getty Images)

The Covid-19 vaccine being developed by Pfizer and its partner BioNTech has shown to be over 90% effective at protecting people against the virus in the ongoing Phase 3 clinical trial, according to an interim analysis by an independent data monitoring committee. “Vaccine candidate was found to be more than 90% effective in preventing Covid-19 in participants without evidence of prior SARS-CoV-2 infection in the first interim efficacy analysis,” the companies announced on November 9. 

Commenting on the results, Dr Albert Bourla, Pfizer Chairman and CEO, emphasized that the first set of results from the Phase 3 Covid-19 vaccine trial provides the “initial evidence of our vaccine’s ability to prevent Covid-19.”

“We are reaching this critical milestone in our vaccine development program at a time when the world needs it most with infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen. With today’s news, we are a significant step closer to providing people around the world with a much-needed breakthrough to help bring an end to this global health crisis. We look forward to sharing additional efficacy and safety data generated from thousands of participants in the coming weeks,” said Dr Bourla.

However, is this a breakthrough and what do we know about this vaccine candidate so far?

What the results say?

The first interim efficacy analysis was conducted on November 8, by an external, independent Data Monitoring Committee (DMC). The analysis evaluated 94 confirmed cases of Covid-19 in trial participants. They received two shots of either the vaccine or the placebo and results revealed that the vaccine was more than 90% effective at seven days after the second dose.

“The case split between vaccinated individuals and those who received the placebo indicates a vaccine efficacy rate above 90%, at 7 days after the second dose. This means that protection is achieved 28 days after the initiation of the vaccination, which consists of a 2-dose schedule. As the study continues, the final vaccine efficacy percentage may vary,” the statement reads. 

How the vaccine works?

Called BNT162b2, it is an mRNA-based vaccine candidate. What this implies is that the vaccine is based on genetic material called mRNA, which targets the spike protein that sits on the outside of the SARS-CoV-2 virus that allows the virus to attach to and invade human cells, initiating infection.

The vaccine introduces this mRNA to the human body, triggering human cells to produce the spike protein. In response to these proteins, the body produces antibodies and other immune pathways are activated, guarding against infection.

The vaccine candidate was found to be more than 90% effective in preventing Covid-19 in participants without evidence of prior SARS-CoV-2 infection in the first interim efficacy analysis, the companies announced on November 9 (Getty Images)

Is it safe?

According to Pfizer, the study enrolled 43,538 participants with 42% of global participants and 30% of US participants having racially and ethnically diverse backgrounds. No serious safety concerns have been observed but safety and additional efficacy data continue to be collected.

“The DMC has not reported any serious safety concerns and recommends that the study continue to collect additional safety and efficacy data as planned. The data will be discussed with regulatory authorities worldwide. The clinical trial will continue through to final analysis at 164 confirmed cases to collect further data and characterize the vaccine candidate’s performance against other study endpoints,” it says.

Pfizer and BioNTech are continuing to gather safety data and currently estimate that a median of two months of safety data following the second (and final) dose of the vaccine candidate – the amount of safety data specified by the US Food and Drug Administration (FDA) in its guidance for potential Emergency Use Authorization – will be available by the third week of November.

Additionally, participants will continue to be monitored for long-term protection and safety for an additional two years after their second dose. “Along with the efficacy data generated from the clinical trial, Pfizer and BioNTech are working to prepare the necessary safety and manufacturing data to submit to the FDA to demonstrate the safety and quality of the vaccine product produced,” it adds. 

Many unanswered questions

The vaccine results were announced via a press release and the details are yet to be published in a peer-reviewed journal. Pfizer and BioNTech plan to submit data from the full Phase 3 trial for scientific peer-review publication.

However, many questions remain. The release does not specify how many of the cases were severe or mild or if different age groups had varying levels of protection. Moreover, it is not known yet whether the vaccine blocked mainly mild cases, or if there is evidence that it seemed to prevent some severe infections, too. It is not known whether the vaccine protects against asymptomatic carriers.

Other aspects such as how long protection via the vaccine might last, and whether it protects those who have previously had coronavirus, are not known. Whether it prevents people from catching the virus, whether it stops virus transmission or just reduces the severity of the symptoms, are also unclear. 

“The data provided in the press release do not provide enough information to assess whether or not the vaccine protects against infection or only against illness. The information provided does not allow us to understand the severity of illness among placebo and vaccine recipients, which it is important to understand, as the objective is not only to prevent symptoms of milder disease but to prevent hospitalization and death. The duration of protection offered cannot be assessed. Pfizer also needs to collect and finalize the safety database so the benefit-risk ratio can be calculated. These data are eagerly anticipated,” states Dr Penny Ward, visiting professor in pharmaceutical medicine at King’s College London.  

Dr Ward explains that if the protection offered is primarily a reduction in risk of disease, but not against infection, then mitigating measures would need to remain in place until sufficient numbers of individuals have been vaccinated to protect those at most risk.

The data monitoring committee has not reported any serious safety concerns and recommends that the study continue to collect additional safety and efficacy data as planned (Getty Images)

Stating that the primary efficacy being reported is based on symptomatic cases, Professor Azra Ghani, chair in infectious disease epidemiology, Imperial College London, emphasizes that “this does not tell us whether it prevents the same level of infections nor anything about onward transmission.” 

Natalie E Dean, a biostatistics expert at the University of Florida, tweeted that while the results are exciting, “of course we will want to independently evaluate them. Unlike treatments, promising data from vaccines do not immediately change the standard of care. The vaccines will undergo a rigorous review process first which will play out over time.”

She adds that information she will be most interested in seeing are how well does the vaccine prevent severe disease, how well does the vaccine prevent infection, and how well it works across different subgroups. 


Pfizer notes, “The study will evaluate the potential for the vaccine candidate to provide protection against Covid-19 in those who have had prior exposure to SARS-CoV-2, as well as vaccine prevention against severe Covid-19 disease.” 

There may be logistical and distribution challenges too. The vaccine has to be stored and shipped and moved at ultra-cold temperatures — minus 94 degrees Fahrenheit or minus 70 degrees Celsius — which could make it hard to get to some places quickly.

What happens now and when will it be available?

Pfizer plans to submit an Emergency Use Authorization (EUA) request to the FDA after the required safety milestone is achieved, which is currently expected to occur in the third week of November. The FDA then needs to decide whether to give emergency approval. It is unclear how long this might take. Even after it is granted EUA, it could be months before the vaccine is available to many people.

Alex Azar, head of the Department of Health and Human Services, said that the FDA will conduct an “independent review process.” Based on current projections, Pfizer expects to produce up to 50 million vaccine doses in 2020 for the whole world, and up to 1.3 billion doses in 2021. Exactly who will qualify for the initial doses has not been decided, but groups that are at higher risk for infection, or are more vulnerable to the virus, are likely to get priority in the US.

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