COVID-19 vaccines: Your biggest questions, answered

·8 min read
As more Americans schedule their COVID-19 vaccine appointments, here's what you need to know about the shots. (Photo: Getty Images)
As more Americans schedule their COVID-19 vaccine appointments, here's what you need to know about the shots. (Photo: Getty Images)

With President Biden announcing an order for 100 million Johnson & Johnson vaccine doses this week, states will soon begin expanding the list of those eligible for vaccination. According to the Centers for Disease Control and Prevention, over 65 million people have received at least one dose of vaccine in the U.S. thus far, with 35 million fully vaccinated. The president is requesting that states ensure all adults are eligible for the vaccine by May 1. And with 2.1 million doses being administered per day, the number of those vaccinated is increasing at a rapid rate.

As Americans schedule their appointments, many questions continue to swirl about how the vaccines work — and how quickly. Here are some common questions answered.

How soon after the first Pfizer or Moderna shot do I get the second one?

Although both the Pfizer and Moderna vaccines generate some immunity after the first shot, studies have shown that both offer the most protection after a second dose is given. The window between the doses varies with each vaccine, so it's important to pay attention to which one you receive. Individuals who are given the Pfizer-BioNTech vaccine need to wait 21 days after the initial dose to the get the second one; those who get the Moderna vaccine must wait 28 days.

How is the Johnson & Johnson vaccine different?

Johnson & Johnson is the third drugmaker to get emergency use authorization from the Food & Drug Administration for its COVID-19 vaccine. Much like the Pfizer and Moderna vaccines, Johnson & Johnson's works by teaching the body how to build the spike protein found on the surface of the SARS-CoV-2 virus — thereby triggering an immune response against it. But unlike its predecessors, this one uses an inactivated virus instead of messenger RNA to carry the genetic code. J&J's single dose proved 72 percent effective at preventing COVID-19 in clinical trials in the U.S., but additional research has shown that the number is likely even higher when it comes to preventing severe disease: 85 percent.

Is the Johnson & Johnson vaccine inferior to the others?

Local news reports show that many people have begun asking to be prioritized for Moderna or Pfizer due to the higher efficacy rates of those vaccines. But Dr. Aditya Shah, an infectious disease specialist at the Mayo Clinic, explains that the numbers may not tell the real story. "Vaccine efficacy percentages only matter when the majority of the population gets vaccinated, that is how it works," Shah says. "Those individual numbers are based on studies done in 40,000, 50,000, 60,000 people — the number is a constant moving target based on how many people get vaccinated."

New York Times journalist Carl Zimmer also pointed out this week on the podcast The Daily that the timeline of the vaccine trials matters. "Pfizer and Moderna started their trial in late July; Johnson & Johnson didn’t start for a couple of months after that. So by the time that Johnson & Johnson had a lot of recruits getting vaccinated, we were in the middle of a really intense surge of COVID, much bigger than what we had dealt with before," Zimmer said. "And what vaccine developers have found is that if you run a trial when rates are really high, you might end up with an efficacy estimate that ends up being low. And that’s just because your volunteers are getting exposed to the virus more."

At what point after getting the COVID-19 vaccine are you immune?

Shah says that both Moderna and Pfizer provide some protection against COVID-19 two weeks after the first dose (Pfizer, 46 percent; Moderna, 92 percent), but that the second dose helps the body ramp up antibodies. "Ideally, [the first dose] needs to be supplemented by the second dose," says Shah. "We don't have enough evidence to say with a good amount of confidence that we should change the recommendation to just do one dose."

In terms of who qualifies as "fully vaccinated" — a term the CDC used this week in new guidance — Shah says, "People can be considered fully vaccinated two weeks or more after they have received the second dose of a two-dose series [either Moderna or Pfizer] or two or more weeks after they have received a single dose of the Johnson & Johnson vaccine. That is when they should be considered immune per the data that we have."

Is it normal to get a fever and body aches after the second vaccine shot?

Yes. Since the arrival of the COVID-19 vaccines, infectious disease experts have warned that the mRNA vaccines in particular have shown more "reactogenicity" than other vaccines — a word used to describe "the physical manifestation of the inflammatory response to vaccination." Recipients of the Moderna or Pfizer vaccine have reported side effects such as fever, body aches, chills and fatigue, all of which should subside in 24 to 48 hours.

In an earlier interview with Yahoo Life, Dr. Gregory Poland, co-director of the Mayo Clinic's Vaccine Research Group, confirmed that these flulike symptoms don't mean you have COVID-19 and shouldn't be cause for concern. "You're likely to have some [local] side effects after the second dose," Poland said. "It doesn't mean anything is going wrong — in fact, it means you're developing a good immune response that will protect you."

Have there been any serious adverse outcomes associated with these vaccines?

Not at this point. The CDC compiles safety data on vaccines through a system called the Vaccine Adverse Event Reporting System, which then investigates any adverse outcomes to see if other people are experiencing something similar. Thus far, the only serious outcome causally linked to any of the three vaccines has been anaphylaxis — a potentially life-threatening allergic reaction that is treatable. Reports of deaths or other serious conditions have to be taken into context, said Susan Ellenberg, professor of biostatistics, medical ethics and health policy at the University of Pennsylvania’s Perelman School of Medicine, in an earlier interview with Yahoo Life.

“The vaccine is intended to prevent illness associated with the infection, but it can’t prevent any other bad things that happen to people,” Ellenberg said. “It’s not going to prevent you from being killed in an automobile accident. It’s not going to prevent you from having a heart attack. All of the things that happen to older people especially. So when you start giving a vaccine to millions and millions of people, all of the bad things that would have happened to people without the vaccine are still going to happen.”

Considering it's a new technology, is mRNA really safe?

Both Pfizer and Moderna rely on a newer technology known as messenger RNA to create immunity to SARS-CoV-2. While some worry about these being the first approved vaccines with this technology, experts have clarified that it's a model that has been studied in humans for almost a decade. In this time, no serious adverse outcomes have been linked to mRNA vaccines. To be sure, although the COVID-19 vaccines rely on technology that has been studied in humans for years, long-term safety data on these particular vaccines has yet to be collected.

Is it OK to hug your grandkid after getting fully vaccinated?

One of the main questions circulating on the internet — "Is it safe to hug my grandkid?" — likely stems from how long Americans have been told to avoid gathering with high-risk individuals outside their household. But multiple experts, as well as the CDC, have now confirmed that it is safe for fully vaccinated people to give their grandkid a squeeze. "The CDC has said that a fully vaccinated person can visit with unvaccinated people from a single household without wearing a mask or physical distancing," says Shah. "So yes, hugging your grandkid should be OK."

How do these vaccines compare with others, such as the flu shot?

Shah does not mince words when talking about the overall picture of the COVID-19 vaccines. "Data that are coming with literally every vaccine — not just in the U.S. but other parts of the world too — are showing extremely promising results," he says. "This amount of efficacious vaccines have not been seen in the history of humanity."

Indeed, all three vaccines currently being distributed in the U.S. have higher efficacy rates than the flu shot, which hovers between 40 and 60 percent each year. But even more effective ones may be on the way. On Friday, U.K. company Novavax released results from clinical trials for its vaccine, which found it to be 96 percent effective. "I know that people are fatigued by this. I am fatigued by it too, but it's just a few more months, and things are already getting better," says Shah. "So get the vaccine. And if you have any questions, then call your local health care provider."

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