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Pfizer and Moderna Covid vaccines 95% effective in clinical trials

Both vaccines performed excellently in clinical trials. What comes next?

BySukee BennettNOVA NextNOVA Next
Doctor administers vaccine to patient

A closeup image of a doctor's hands, vaccine, and patient's arm. Image credit: SELF Magazine

Today, Pfizer and BioNTech announced that their new experimental Covid-19 vaccine is 95% effective in preventing infections and causes no serious safety concerns, according to a final analysis of their clinical trial.

"Efficacy was consistent across age, race and ethnicity demographics. The observed efficacy in adults over 65 years of age was over 94%," Pfizer and its German partner BioNTech said in a joint statement.

The news comes just two days after the biotech company Moderna Inc. said its experimental vaccine was 94.5% effective in preventing disease, according to an analysis of its Phase 3 clinical trial. Last week, Pfizer and BioNTech had announced that their vaccine was more than 90% effective. Both vaccines use new mRNA technology.

Moderna’s study involved 30,000 volunteers. Half of those volunteers received its coronavirus vaccine twice 28 days apart and the other half received two doses of a placebo on the same schedule.

“There were 95 instances of Covid-19 illness among the study participants; only five of those cases were in the vaccinated group,” Joe Palca writes for NPR. “Ninety were in the group receiving the placebo. Of these, there were 11 cases of severe disease. The results indicate the vaccine was inducing the kind of immune response that protects people if they were exposed to the coronavirus.”

The results for Pfizer and BioNTech’s vaccine also come from interim analyses of a large Phase 3 clinical study, which has not yet been peer reviewed by other scientists. The companies’ trial has enrolled more than 43,000 volunteers in six countries to date, and 38,955 of them have completed its vaccine regimen so far. Pfizer and BioNTech’s regimen also consisted of two vaccine injections or two placebo injections, spaced three weeks apart.

Pfizer “counted 170 cases of coronavirus infection among volunteers who took part in the trial. It said 162 infections were in people who got placebo, or plain saline shots, while eight cases were in participants who got the actual vaccine,” Maggie Fox and Amanda Sealy write for CNN.

Moderna and Pfizer used slightly different protocols to identify Covid-19-positive study participants. Participants in the Moderna study had to have at least two Covid-19 symptoms and a positive test result to be counted as a Covid-19 case. Moderna waited 14 days following the second injection to begin counting cases. Pfizer required one Covid-19 symptom and no test to be counted as a positive case, and it started counting cases at seven days, Palca writes.

The companies’ vaccines, however, were strikingly similar. A traditional vaccine, like your annual flu shot, uses killed or weakened versions of a virus, or a piece of the virus, to prepare your immune system to recognize and fight off the living virus if you come in contact with it. Conversely, these two new experimental mRNA vaccines attempt to help the body produce one small component of the virus itself that the immune system can learn from. RNA “is kind of an ancient cousin of DNA,” Rhiju Das told NOVA in April. “RNA molecules are the scripts that viruses use and that our human bodies also use to make proteins.” (mRNA refers specifically to messenger RNA.)

The coronavirus’s RNA codes for at least 24 proteins, including the spike protein, which covers its exterior. The virus uses its spike protein to bind to and enter our cells, where it then injects its RNA, hijacking our human cells to make many more copies of the virus.

“It’s almost like a skeleton key for a lock, opening a portal within human cells that the virus can slip in,” Das told NOVA.

Both Moderna’s and Pfizer’s mRNA vaccines prompt a person’s cells to produce the SARS-CoV-2’s spike protein, so their immune system can learn to recognize it and develop Covid-19-fighting antibodies without having any contact with the actual virus.

“Our bodies won’t make a full-fledged infectious virus,” Das said. “They’ll just make a little piece and then learn to recognize it and then get ready to destroy the virus if it then later comes and invades us.”

Moderna and Pfizer are still gathering safety data that the Food and Drug Administration requires for consideration of an emergency use authorization. This authorization would allow vaccine manufacturers to distribute their vaccines during the pandemic at an earlier date than otherwise possible. “To apply for an emergency use authorization, the FDA requires that half of participants have at least two months of data regarding a Covid-19 vaccine’s safety after they receive the final dose. For Pfizer and BioNTech’s vaccine, that point is expected to come in the third week of November,” Erin Garcia de Jesús writes for Science News.

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Both companies plan to apply for FDA emergency use authorization this month. Moderna stated Monday that it expects to be able to ship about 20 million vaccine doses in the U.S. by the end of this year and another 500 million to 1 billion in 2021, if authorized to do so. Pfizer expects to produce up to 50 million vaccine doses in 2020, and 1.3 billion in 2021, if authorized.

To prepare to store a hopefully forthcoming coronavirus vaccine, large urban hospitals across the U.S. are rushing to buy expensive ultra-cold freezers. (Last week, Pfizer and BioNTech said that their vaccine needs to be stored at minus 94 F. Conversely, Moderna states that its vaccine can be safely stored in freezers at about 25 F for 30-day storage, “a temperature easily reached by a home refrigerator freezer,” Palca writes. However, safe 6-month storage would require a temperature of minus 4 F, Moderna stated in a press release.) Most rural hospitals can’t afford ultra-cold freezers, “meaning health workers and residents in those communities may have difficulty getting the shots,” Olivia Goldhill reports for STAT News.

Medical experts call the temperature-controlled supply chain of vaccines and other protein-based pharmaceuticals the “cold chain,” because the protein molecules in these products can break down at higher temperatures, rendering them ineffective.

“Maintaining vaccines continuously at their required temperature is already one of the biggest challenges developing countries face with routine immunization, and this will only be exacerbated with the introduction of a new [coronavirus] vaccine,” Toby Peters writes for WIRED.

In a paper published in May in the journal Science, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, suggested that the U.S. population alone may require several different vaccines made and distributed by different labs to bring an end to the pandemic, which, according to Johns Hopkins University’s Covid-19 dashboard, has so far sickened more than 11.3 million Americans and more than 55.7 million people worldwide.

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