Study: Pfizer vaccine less effective in older patients

The effectiveness of the Pfizer COVID-19 vaccine diminishes as patients get older, according to a new study by UT Southwestern Medical Center researchers.

Scientists analyzed blood samples from 51 adults ranging in age from 21 to 82 who had gotten both doses of the Pfizer-biontech vaccine to measure the effectiveness of the antibodies generated by the MRNA shot series. They found that the antibodies generated by people older than 65 were less effective at performing antiviral functions than in people under 65.

Antibodies are proteins produced by the immune system to attach to foreign matter, like viruses, so the body knows which pathogens to destroy. The Pfizer vaccine contains a piece of MRNA specific to the COVID-19 virus’s spike protein, which the virus uses to infect human cells.

“The fact that these antibody functions decrease with age is one reason why the elderly are still more susceptible to severe illness with COVID-19 and highlights the need to develop different approaches for older, vulnerable individuals,” said lead author Dr. Lenette Lu, assistant professor of internal medicine and immunology in the UT Southwestern Division of Infectious Diseases and Geographic Medicine.

Nearly three years after the beginning of the pandemic, COVID-19 finally appears to be easing its grip on the U.S. health care system. But the virus, first discovered in 2019, can still wreak havoc on the elderly and people with compromised immune systems.

New variants, like the highly contagious delta and omicron strains, are also more effective at evading immune responses than the original COVID-19 strain. BA.5, the omicron subvariant that became the dominant circulating strain this summer, is now losing ground to a handful of other subvariants, like BQ.1 and BQ.1.1.

While the COVID-19 vaccine is less effective at preventing all illness from the new variants, it can still help prevent severe disease and death.

When the UT Southwestern researchers evaluated the antibodies generated by study participants, they found that the antibodies helped activate immune cells that could affect the virus after it infected the body.

“Even if an antibody is less able to prevent variants of a virus from infection, it can still block the development of symptoms, disease severity and spread from one person to another,” Lu said.

The antibodies in people under 65 carried out more antiviral activities than in people over 65, the study said. This may be because of sugars attached to the antibodies that change with age, limiting antibody function.

Though the study was relatively small, the data suggests updated vaccines could be particularly important for older adults. Continuing to study COVID-19 vaccines and how they affect the immune system is also important so scientists can better understand how to make effective vaccines in the future, Lu said.

A new, bivalent booster dose that targets both the original and omicron COVID-19 variants is now available for anyone 5 and older who received their previous COVID-19 dose at least two months prior.

Uptake of the new booster recipe has been slow. Only 12 percent of people 5 and older in the U.S. have received the updated shot, according to Centers for Disease Control and Prevention data. Just last week, the Biden administration announced a six-week push to get more Americans boosted ahead of the holiday season.

Public health experts still urge people eligible for the COVID-19 vaccine to get the shot series, even though the current subvariants are far less deadly for people who have some form of immunity against the virus.

“The problem with a lot of people getting infected, even if they’re not being hospitalized or dying, is that that means the virus is replicating and can be making new variants,” said Catherine Troisi, an infectious disease epidemiologist with Uthealth Houston School of Public Health.

“There’s no guarantee that a new variant that does cause more infection or is better at evading the immune system could not arise,” she said.