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On Monday, Nov. 9, Pfizer and BioNTech — the pharmaceutical companies currently leading a phase 3 coronavirus vaccine trial, in which efficacy and safety tests are being conducted — issued a press release explaining how their COVID-19 vaccine candidate had prevented the disease in over 90 percent of enrolled volunteers who had no evidence of previous coronavirus infection.

Approximately 250 volunteers were enrolled in the Pfizer trials through a partnership between the Yale New Haven Hospital and the Yale Center for Clinical Investigation, according to Chief Medical Officer of the Yale New Haven Hospital Thomas Balcezak. At Yale, associate professor of medicine Onyema Ogbuagu is currently leading this study, as well as other clinical trials for COVID-19 therapies. Approximately 43,500 people around the world are participating in the Pfizer vaccine trials — half of whom have received the actual vaccine and half of whom were injected with a placebo. Out of all enrollees, there were 94 confirmed cases of COVID-19 infection thus far, with the majority of them concentrated among volunteers who received the placebo, according to Balcezak.

“While we don’t have that data in a peer-reviewed publication to review, it is being overseen by the FDA and the data safety monitoring board of the FDA,” Balcezak said in a press conference on Wednesday. “I have great personal confidence that they’re doing a great job there, and I think we will be seeing that vaccine in a few short weeks.”

Balcezak explained that although these results are encouraging, they are only the product of interim, or provisory, analyses. For the trial to conclude, the FDA and Pfizer defined 164 confirmed COVID-19 cases as the threshold that would provide a reasonable level of confidence in the vaccine’s safety. Once 164 of the volunteers test positive, statisticians will identify which of them received the placebo versus the vaccine, allowing them to calculate a final measure of efficacy.

In an email to the News, Richard Martinello –– medical director of infection prevention at the YNHH and associate professor at the School of Medicine –– emphasized the need for “cautious optimism” in response to these interim results. He explained that until complete reports or peer-reviewed manuscripts are publicized, news releases on vaccines should be taken with a grain of salt.

“While press releases are great to rapidly communicate high level findings and conclusions from research, these reports lack the detail required for an in-depth understanding of the research and the necessary consideration of the limitations of those findings,” Martinello wrote. “Cautious optimism is warranted until a complete report is presented as a peer reviewed manuscript.”

Pfizer’s CEO, Albert Bourla, called the date of the press release a “great day for science and humanity” and suggested that by the end of November, the company may be ready to apply for Emergency Use Authorization through the Food and Drug Administration.

One of the concerns that physicians and public health experts have raised regarding the Pfizer vaccine candidate relates to its cold chain requirements. The vaccine has to be stored at minus 70 degrees Celsius to prevent the decomposition of the viral genetic material it contains. These requirements could pose challenges in terms of distribution if the Pfizer vaccine were the only candidate available, experts have suggested. In addition, the fact that the Pfizer vaccine requires two doses for immunization has also been identified as a potential difficulty in reaching community immunity.

According to Balcezak, Pfizer is able to ship their vaccines in a super cooler with dry ice to the centers that are currently administering it in trials. He also explained that the U.S. Army has been assisting in the logistics of this dispatch.

Balcezak added that the YNHH is collaborating with the Connecticut Hospital Association to organize the distribution of the vaccine when it becomes available. He also pointed out that professionals at the YNHH are familiar with the Pfizer vaccine candidate’s challenging requirements, as they had to store and then thaw it to administer it to volunteers.

“We have capacity for storing up to 50,000 doses right now within our freezers, and we are actively pursuing the addition of more of those freezers,” Balcezak said.

According to Co-Director of the Yale Center for Clinical Investigation Brian Smith, one of the main challenges the team is facing is patient recruitment, since the prevalence of the virus during pandemics changes over time and geographically. Fluctuating case numbers make it hard to predict how much risk of exposure the participants face. Smith also explained the importance of having a diverse sample population take part in the trials.

“For vaccine trials it is important to include diverse patient populations who are at sufficient risk of viral transmission that one can assess the efficacy of the vaccine,” Smith wrote in an email to the News.

Smith explained that to circumvent this challenge, the YCCI has benefited from its Cultural Ambassadors program, a 10-year partnership between the center and community leadership in New Haven. According to Smith, the program has been “particularly instrumental” in recruitment of a diverse participant pool.

Smith also wrote that the vaccine’s high efficacy rate, observed this early in the clinical trials, is encouraging. Martinello, who is a member of Gov. Lamont’s vaccine advisory group, believes that 90 percent efficacy compares extremely well to other vaccines against different diseases.

“90% efficacy is excellent,” Martinello wrote. “As a comparison, a meta-analysis estimated the influenza vaccine to be 59% efficacious to prevent lab-proven influenza among adults. The [measles, mumps and rubella] vaccine is estimated to be about 95% efficacious.”

There are around 60 studies currently being conducted at Yale relating to different aspects of the coronavirus pandemic, according to Smith. These studies range from therapeutic trials to the analysis of viral structure and behavior. The YCCI is also planning on developing a collaboration with Merck — another pharmaceutical company with a COVID-19 vaccine in human clinical trials.

According to the New York Times’ vaccine tracker, there are currently 53 vaccines being tested in human clinical trials.

Beatriz Horta | beatriz.horta@yale.edu

Maria Fernanda Pacheco | maria.pacheco@yale.edu

Correction, Nov. 14: A previous version of the article stated that the Pfizer vaccine candidate prevented COVID-19 transmission in over 90 percent of candidates. The article has been updated to reflect that the data referred to COVID-19 infection, not transmission.