By Jonny Lupsha, News Writer

Two vaccines for the coronavirus have each proven over 90% effective, BuzzFeed reported. Although no timeline can be promised, health experts believe mass vaccinations could begin in April 2021. How good is 95% when it comes to vaccines?

According to BuzzFeed, a long-awaited piece of good news about the coronavirus may be just around the corner as two candidate vaccines appear to be very effective. “The promising new results from Moderna suggested that its vaccine is 94.5% effective at preventing COVID-19, coming just one week after the drug company Pfizer reported better than 90% effectiveness in its early data,” the article said.

“Both firms say they will request emergency authorization from the FDA within weeks, kicking off a long-anticipated start of the campaign to vaccinate the United States.”

Is 95% considered effective enough? And how do vaccines work?

High Odds

The BuzzFeed article said that the FDA set a minimum of 50% effectiveness as a rate for a vaccine to qualify for use, in its summer guidelines for vaccine makers. It also said that Dr. Anthony Fauci, chief of the National Institute of Allergy and Infectious Diseases, said he’d hoped for 70-75% effectiveness in a coronavirus vaccine. The 94.5% rate of Moderna’s vaccine not only exceeds both rates, but it also compares well with efficacy rates of established vaccines used in disease prevention.

“The evidence is extremely clear: Vaccines are about 95% effective,” said Dr. Steven Novella, Assistant Professor of Neurology at the Yale School of Medicine. “This means that 95% of people who are vaccinated with a vaccination schedule—which may involve boosters—will develop a functional immunity to the substance against which they’re being vaccinated.”

However, vaccines are generally less effective in the elderly and in people with compromised immune systems, which is concerning since they need vaccines the most. This is where the theory of herd immunity comes in.

“There are estimates that when about 90% or more of any population—people who are likely to be exposed to each other—are vaccinated against an infection, you achieve herd immunity,” Dr. Novella said. “That infection cannot spread easily from person to person. Anyone who is harboring the virus or bacteria is very unlikely to encounter somebody else who isn’t immune.

“Therefore, they’ll be able to fight it off before they spread it around, [which] prevents outbreaks and also prevents infections from being endemic.”

A Brief History Vaccines

Dr. Novella said that vaccines work by provoking a response from our immune system that’s targeted at something it’s encountering for the first time. At first contact, the response takes five to 10 days while the body learns to fight the new substance. Subsequent exposures work after one to three days.

“The most primitive type of vaccines, called inoculations, utilized living viruses or bacteria and was essentially just a controlled infection,” he said. “The next step was the development of an attenuated virus or bacteria. The process of attenuation is to breed it in another species so that it will be less virulent in humans.”

Attenuated vaccines allowed the body to develop immunity, but came with a risk of mutation. Then there are inactivated vaccines, in which a virus that has been rendered unable to replicate is introduced to the system so the body can easily learn to recognize and defeat it.

Subunit vaccines only contain a part of the virus, like its protein shell, so there’s zero risk of infection; while toxoid vaccines are vaccinations against a toxin that the virus produces. This way, the infection can run its course and the body can learn to fight the virus, but without any negative health consequences.

More details about the coronavirus vaccines will likely be announced by manufacturers soon.

This article was proofread and copyedited by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Dr. Steven Novella contributed to this article. Dr. Novella is Assistant Professor of Neurology at the Yale School of Medicine. He earned his MD from Georgetown University and completed his residency training in neurology at Yale University.