The Food and Drug Administration (FDA) advisors have begun to review Emergency Use Authorization (EUA) for the first two COVID-19 vaccines, much-awaited remedies since the pandemic began last spring. If approved, the Pfizer-BioNTech and Moderna Inc. vaccines will begin to arrive at health departments and hospitals shortly after. Patients will likely have a myriad of questions about their availability, efficacy, safety and potential side effects. Here’s a quick vaccine cheat sheet to keep handy when the phones start ringing.

The COVID-19 mRNA vaccine is a new type of inoculation. Is it safe and effective?

The mRNA, or messenger RNA vaccines, developed independently by Pfizer and Moderna, are indeed different from prior vaccines administered to humans. The traditional vaccines typically expose people to either dead or weakened pathogens, prompting the immune system to mount a response. The mRNA vaccine injects a snippet of the SARS-CoV-2 genetic code into human cells, which then produce the coronavirus’s spike proteins. That triggers an immune system response and generates neutralizing antibodies. While these are the first mRNA vaccines to be licensed for human use, the technology had previously been used in some Phase 1 trials that used the mRNA technology and didn’t find safety concerns, says Brian Garibaldi, associate professor in the Division of Pulmonary and Critical Care Medicine at Johns Hopkins. Bruce Walker, professor of immunology and infectious diseases at Harvard Medical School, adds that the mRNA method was used in the development of Ebola and cytomegalovirus vaccines, but those haven’t been approved yet. More traditional vaccines are also in the works, but their development takes longer than the mRNA ones. And the fact that the two available vaccines are 90% to 95% effective is “a grand slam home run,” notes Warner Greene, director emeritus of Gladstone Institute of Virology and Immunology. “It is a triumph of science over the disease.”

Most vaccines take years to develop, but the COVID-19 vaccines have been part of Operation Warp Speed (OWS), arriving within months. How do we know the trials have gathered enough data for efficacy and side effects?


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Most vaccines take a few years to develop, but COVID-19 posed such a tremendous threat to people and societies that scientists worldwide joined forces to accelerate the timeline. Also, some of the early vaccine research had been done in the aftermath of the 2003 outbreak of SARS, a close cousin of SARS-CoV-2; those early candidates were on their way to clinical trials. Typically, the FDA evaluates several years worth of data to license a health product, but the agency can grant an EUA to vaccines that pass the safety and efficacy requirements, explains Margaret Hamburg, a former FDA commissioner. The FDA and vaccine-makers will also continue gathering the data while vaccines are being administered. Nonetheless, so far, the data from trials shows that the benefits outweigh the potential side effects. The Pfizer-BioNTech vaccine demonstrated 95% efficiency, which means that 95% of people who received it did not fall ill with COVID-19, says Greene. And the 5% who did get sick did not develop severe disease, Greene points out. The bottom line is — it’s safer to get the vaccine than risk contracting the disease.

How will these vaccines be distributed, and when can my family and I get them?

The Centers for Diseases Control (CDC) has an advisory committee whose job is to develop vaccine distribution proposals, explains Robin Alta Charo, professor of law and bioethics at the University of Wisconsin Madison. Once approved, these recommendations will be shared with the states’ health departments, which will receive vaccine batches and route them to health institutions. Your personal vaccination timeline will depend on your occupation, age and risk factors. The CDC recommended that frontline healthcare workers and residents of nursing homes and long-term care facilities receive the vaccines first. Next in line will be the workers in essential and critical industries, people with underlying medical conditions and adults over 65.

Will I be contagious or have a mild case of COVID-19 once I receive the vaccine?

The COVID-19 vaccine will not make you contagious, but you may have some flu-like symptoms, including headache, body aches and even fever, as your body mounts an immune response. The mRNA vaccines are given in two doses with several weeks in between, and the second dose seems to produce stronger side effects, but they usually don’t last long. Despite the side effects, it is critically important to receive both doses to develop immunity. Notably, the majority of the trial volunteers had very mild side effects, such as pain at the injection site, which is similar to many other vaccines.

How long will my immunity last? Some studies found that the antibodies to the coronavirus disappear after only a couple of months.

It is true that the strong, neutralizing antibodies to the SARS-CoV-2 virus disappear quickly—about 60% of people lose them within 60 days after infection, Greene says. But that doesn’t mean that vaccines’ protection will only last two months. If vaccines can create memory B cells, which will remember the virus and produce the antibodies should people contract it again, the immunity will last longer. There were also signs that the vaccines engendered a strong response from T cells, another type of immune system warrior that actively fights the virus. So the hope is that even though people may contract the virus months later, they would develop only mild symptoms, such as a cough, but not pneumonia, Greene says. Walker also thinks there are reasons for optimism. “New data from Moderna suggest that immunity is sustained at least since the first doses were given last spring,” he says.

Can I stop wearing my mask or travel to see my family once I get the vaccine?

Not immediately. The vaccine will prevent you from developing severe disease, but it won’t prevent you from contracting it and passing it to other people, who may not yet be vaccinated, explains Nancy Messonnier, the CDC’s director of the National Center for Immunization and Respiratory Diseases, who leads the COVID-19 vaccine program. So until a significant proportion of the population receives the vaccines, we will have to continue wearing masks and practice social distancing. That’s why it’s important to vaccinate as many people as possible, achieving so-called herd immunity, or community immunity. “If everybody got vaccinated, we’d be all protected,” Messonnier says.