Among the unknowns: To what extent does the vaccine prevent infection vs. simply preventing clinical illness?
Can a vaccinated person who becomes infected, but not sick, transmit the virus to someone else? That’s a pivotal factor in forecasting how rapidly the pandemic will be quashed once there is widespread distribution of vaccines.
Another unknown: How long will the protective effect of the vaccine last?
Scientists will also be vigilant for severe allergic reactions. Last week, two health-care workers in the United Kingdom who were among the first batch of people to get the vaccine after it was authorized developed anaphylaxis, a severe allergic response.
Both were known to have a history of severe allergic reactions, and both were treated and recovered. A third person reportedly suffered a rapid heartbeat. British authorities issued new guidance saying people with a history of anaphylaxis should consult with their doctor before taking the vaccine. Researchers do not know what substance in the vaccine formula triggered the severe allergic response.
“When you make a decision to launch a vaccine like this, it’s not because you know everything,” said Paul Offit, a pediatrician and vaccine expert at Children’s Hospital of Philadelphia and member of a Food and Drug Administration advisory panel that endorsed the vaccine Thursday. But, he added, “I think we know enough.”
Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said Saturday, “I don’t think that the allergic reactions are even close to being a showstopper for the Pfizer vaccine.”
He said the criteria for participation in the random trials excluded people with a history of severe allergic reactions, and it is not surprising that, as the vaccine reached the general population, such rare allergic responses emerged. He said officials will continue to monitor the safety of the vaccines long after they have received emergency authorization.
“Observation of safety does not end when you start administering vaccines to the general public,” he said.
The big picture is that covid-19, the illness caused by the coronavirus, is a known killer, and has already taken nearly 300,000 lives in the United States and more than 1 million worldwide. Vaccines are essential to crushing the pandemic. U.S. public health officials hope at least 70 percent of the population will agree to be inoculated with one of the vaccines rolled out in the coming months.
“I feel like we’re doing something historic, and there’s multiple vaccines, and we should be able to lick this,” said immunologist Stanley Perlman of the University of Iowa, who is also a member of the advisory panel that voted Thursday to recommend the Pfizer-BioNTech vaccine.
But he acknowledged he is concerned about potential side effects that may not yet have been identified.
“I worry about something coming up that we don’t know anything about. The unknown,” he said.
Two criteria for a good vaccine are “effective” and “safe.” The coronavirus vaccine technically named BNT162b2 and developed by industry giant Pfizer and BioNTech meets both standards, according to the professionals who have developed the vaccine, conducted randomized clinical trials and reviewed resulting data during the past several months.
It has received emergency authorization from the FDA and from regulators in the United Kingdom, Canada, Bahrain, Mexico and Saudi Arabia. Another, similar vaccine from biotechnology company Moderna is poised to be greenlighted by the FDA this week after a meeting of an advisory panel.
Data from the randomized Pfizer-BioNTech trial showed the two-dose vaccine to be 100 percent effective in preventing severe illness from covid-19.
But in roughly half the people who get the shot, it can produce modest side effects, including fever, headache, fatigue and pain at the injection site. That’s typical for most vaccines.
This is not a flaw or a failure, vaccine experts hasten to point out. Side effects are a sign the immune system is kicking into gear, as intended. They’re a feature and not a bug, to borrow the language of computer programmers.
“Things like fever or soreness at the injection site are normal, and actually they indicate that your body is reacting to the vaccine, which is what you want,” said Ellen F. Foxman, an immunologist at the Yale School of Medicine. “That’s a good thing.”
Side effects were roughly the same in trial volunteers who got the vaccine and those who got a saltwater placebo.
“The immune system needs a better public-relations team, because it’s just the immune system doing what it does,” Offit said.
The newly authorized vaccine, like the Moderna shot, uses a synthesized scrap of genetic information, called messenger RNA, that is wrapped in a protective fat layer to keep it from disintegrating. When it goes into cells in the muscle of the upper arm, it incites cellular machinery to manufacture a protein that mimics the shape of the spike protein that protrudes from the surface of the coronavirus.
At no point, in this type of vaccine, is the coronavirus itself or even part of the coronavirus injected into the body. The body, in effect, becomes the vaccine maker, creating a new protein that triggers an immune response. The immune system manufactures antibodies that can disable anything with structural features resembling this protein — including the coronavirus.
Such a vaccine has never been deployed before.
“It’s very important to think about the whole picture,” Foxman said. “The vaccine prevents a disease that we know has a lot of bad outcomes, right? Mortality is an outcome — death.”
She added: “To me, it’s very clear it’s very beneficial to avoid all the known problems of getting covid-19. I would take this vaccine in a minute if I were offered it.”