Moderna's COVID-19 Vaccine May Be Best for Seniors - Everyday Health

Trying to decide what kind of COVID-19 vaccine to get? While the risk of experiencing complications after receiving any type of mRNA shot is exceptionally low, a new study revealed that older adults were somewhat less likely to have serious issues after getting a first dose of the Moderna vaccine compared with those who got the Pfizer-BioNTech shot.

In a paper published this week in JAMA Network Open, scientists also found that older adults (average age 76) who received Moderna had a 14 percent lower risk of being diagnosed with COVID-19 compared with those who received Pfizer.

"The Moderna vaccine was associated with a slightly reduced risk of some adverse events, but it's also a more effective vaccine," says lead study author Daniel Harris, PhD, an epidemiologist and research scientist in the Center for Gerontology and Healthcare Research at the Brown University School of Public Health in Providence, Rhode Island. "The reduction in COVID-19 risk may likely have this downstream impact that reduces the risk of adverse events like pulmonary embolism [a sudden blockage in a lung artery]."

The overall analysis showed that the risk of adverse events was very low in both vaccine groups, and the vaccines did not differ in risk for most outcomes.

Researchers Analyzed Data From Over 6 Million People

The research team analyzed customer data from two large pharmacy chains linked to Medicare claims. Participants included more than six million adults age 66 and older who had received an mRNA dose between December 11, 2020, and July 11, 2021. Nearly 6 in 10 were women and 86.5 percent were white. About 3.3 million had received Pfizer while 2.9 million had received Moderna.

When looking at 12 possible negative health outcomes during 28 days after a first dose was administered, the Moderna group had a 4 percent lower risk of pulmonary embolism and a 2 percent lower risk of thromboembolic events (several conditions related to blood clotting).

Dr. Harris notes that the risk of adverse events from a natural COVID-19 virus infection is substantially higher than the risk of adverse events from either mRNA vaccine.

Moderna's COVID-19 Vaccine Has the Highest Levels of mRNA

Sean Leng, MD, director of the Johns Hopkins Center on Aging and Immune Remodeling in the Division of Geriatric Medicine and Gerontology, says that the results were not surprising given that Moderna contains 100 micrograms of mRNA while Pfizer contains 30 micrograms.

Nucleoside-modified mRNA teaches cells how to make a protein that triggers an immune response.

"With the higher amount of antigen [substance that triggers an immune response] in the vaccine, that should be able to actually stimulate a more robust response," says Dr. Leng, who was not involved in the study.

This current research, however, did not examine what mechanisms may be making the Moderna vaccine more effective.

In the Frail Elderly, Vaccine Differences Were Smaller

Harris and his colleagues also compared outcomes specifically among older adults who are defined as being frail. Measures of frailty take into account many factors, including loss of energy, physical ability, and cognition, and general health. Frail individuals may have multiple chronic conditions, such as diabetes, heart disease, and cancer.

In frail older adults who received Moderna, the risk difference of being infected with COVID-19 went down to 6 percent, and there was no significant risk difference for pulmonary embolism between the Moderna vaccine and the Pfizer vaccine, according to Harris.

"As you become more frail, the differences between the Moderna vaccine and the Pfizer vaccine become smaller," he says. "This sends a message that we should be thinking about frailty level when we're designing these types of vaccines, and we may possibly need a higher dose COVID vaccine for folks who have frailty."

The differences in risk from the two vaccines become less pronounced in part because the more frail a person becomes, the harder it is to mount an immune response, Leng explains.

What's Ahead for COVID-19 Vaccines?

Public health officials are expecting a new formulation of the COVID-19 vaccines for use in the United States beginning in the fall. As new shots are developed to address new strains of the virus, the differences between mRNA brands may change in unknown ways.

"You can imagine regularly updating these types of analyses as new vaccines are developed," Harris says. "Depending on which one comes out on top, even on a very small scale, that may have big implications at the population level and render a preference for that particular vaccine."

With all this in mind, Leng still urges older Americans to get their booster shots.

"We don't know for sure if new boosters will stimulate a stronger response than prior vaccination, but at least they should help to sustain immunity," he says.

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