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The Medical Minute: What you need to know about the COVID-19 vaccine

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A Food and Drug Administration (FDA) panel could vote as early as today on whether to grant emergency use authorization (EUA) for Pfizer’s COVID-19 vaccine. Next week, Moderna plans to seek EUA for its vaccine. Distribution could begin immediately if authorized.

A new type of vaccine

The COVID-19 vaccines from Pfizer and Moderna were developed using a technology called messenger RNA, or mRNA. Traditionally, many vaccines — including the seasonal flu shots — have included a weakened or inactivated virus to trigger an immune response in our bodies. An mRNA vaccine instead introduces genetic material that causes our cells to create a protein — in this case COVID’s spike protein, explains Dr. Thomas Ma, chair of the Department of Medicine at Penn State Health Milton S. Hershey Medical Center. Our immune system then creates a response.

“This type of vaccine — mRNA — has been studied before,” said Dr. Catharine Paules, an infectious diseases physician at the Milton S. Hershey Medical Center. “But this will be the first time they’ve been authorized for use broadly in the United States.”

According to the Centers for Disease Control and Prevention (CDC), the vaccines will be administered into the upper arm, just like flu shots. But unlike the seasonal influenza vaccine, two doses are required for the COVID vaccine.

“There’s likely a limited response after just one dose,” Paules said. “However, without that second dose, you won’t have as much of an immune response and you may not be fully protected against illness.” Pfizer’s vaccines should be administered in two doses 21 days apart, while Moderna’s will be given 28 days apart.

“The vaccine is a scarce resource right now,” Paules said. “So people should be sure that when they request the first dose, they’ll be able to follow through with the second.” The FDA is drafting guidelines for what to do if a patient has to delay the second dose.

Effectiveness and side effects

“The progress made in developing these vaccines has been remarkable,” Ma said. “There have been no shortcuts — the process has been vigorous. And the vaccines’ efficacies are truly impressive.”

Although the FDA had indicated that it was willing to authorize a vaccine with 50% efficacy — meaning that half of the people who received it would be adequately protected from the COVID-19 virus — the efficacy of the two vaccines on track for authorization in the United States are significantly higher, at 95% for Pfizer’s and 94% for Moderna’s.

“These results show that the vaccine can really help — especially high-risk patients,” Ma said. “It will significantly protect individuals from getting the virus, and if they do still get it, it will protect them from becoming seriously ill.”

One concern with vaccines is whether they can keep up with mutating viruses. This is a recurring problem with the flu, but Paules says it should be less of a concern with the virus that causes COVID-19.

“Coronaviruses have what’s called a proofreading mechanism,” she explained. This means they are able to correct mistakes when they happen during replication, limiting mutation. “This is one reason we’re hopeful that these COVID vaccines will maintain their efficacy over time.”

One unknown is long-term side effects. Ma notes that currently, “We only know about short-term side effects. So far it looks good. But we want to know how the vaccine is doing after six months or a year. What about side effects after four months, six months, a year,” Ma said. “Will unusual things pop up?”

These vaccines have gone through phase 3 clinical trials, meaning they’ve been tested in 30,000 to 40,000 people, Paules said. “But sometimes you don’t see very rare side effects until those numbers reach the millions. It is important that safety data continue to be collected as the vaccine is distributed throughout the U.S.”

Health officials in Britain have warned that people should not receive the shot if they have had a significant allergic reaction to a vaccine, medicine or food, including those who have been told to carry an EpiPen or similar device.

Maintaining masking and social distancing

The CDC’s Advisory Committee for Immunization Practices has recommended that the first wave of COVID vaccines be administered to health care workers and nursing home residents. After they’ve received their second dose, these populations will likely have very good protection against the virus. But that doesn’t mean that they can’t transmit COVID-19 to others.

“Right now, we just don’t know,” Paules said. “It’s conceivable you can still get infected. You’re protected against developing illness, but not necessarily against shedding the virus and spreading it onto others.”

Both Ma and Paules warn against letting our guard down once people start getting vaccines.

“We can’t relax with things like social distancing and wearing masks until we get more data and more guidance from public health officials,” Ma cautioned.

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The Medical Minute is a weekly health news feature produced by Penn State Health. Articles feature the expertise of faculty, physicians and staff, and are designed to offer timely, relevant health information of interest to a broad audience.

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