New study underscores need for COVID-19 booster shots for older adults

Results of the study, published Aug. 15 in Clinical Infectious Diseases, directly support the CDC vaccination guidelines recommending COVID-19 boosters, investigators say.

A previous study documented a significant decline in protective antibody response among all vaccine recipients six months after an initial two-dose series of mRNA vaccines, particularly in older adults whose immune systems weaken with age and respond less efficiently to viral and bacterial infections. These previous studies also showed a sharper decline in immune response in men compared with women in adults over 74 years.

During clinical trials of the mRNA COVID-19 vaccines prior to approval by the U.S. Food and Drug Administration, antibody response was shown to be high in older adults, conferring robust protection against infection and hospitalization. However, continued monitoring of these individuals showed a decline in antibodies after six months.

For the new study, investigators at Johns Hopkins Medicine tested COVID-19 antibody levels in blood samples from more than 80 adults ages 75-98 who had two initial doses of the mRNA vaccines made by either Pfizer or Moderna and no known history of COVID infection.

As a comparison group, researchers also tested the blood of 84 adults under 75 years old with the same vaccination and infection history.

These initial samples showed that the older adults had overall three to eight times lower antibody levels than the younger group, but older males in particular had one to three times lower antibody levels than their female counterparts.

However, when blood samples were again taken and tested 14-30 days after a booster shot, antibody levels for older adults matched those in the younger group. A third dose also eliminated disparities between males and females within the same age group.

"The data support the CDC guidelines for COVID-19 vaccination and affirm that the vaccine is initially able to mount a good antibody response," says Sean Leng, M.D., Ph.D., a professor of medicine who specializes in geriatric medicine at the Johns Hopkins University School of Medicine. But, he adds, older people need to be especially encouraged to get the vaccine and boosters to keep them protected from breakthrough infections as immunity wanes.

Leng says the study also underscores the importance of continued research on factors that may affect immunity, such as type of vaccine, age, sex and frailty.

Other scientists who contributed to this research include Janna Shapiro, Ioannis Sitaras, Han Sol Park, Tihitina Aytenfisu, Christopher Caputo, Maggie Li, John Lee, Trevor Johnston, Huifen Li, Camille Wouters, Pricila Hauk, Henning Jacobsen, Yukang Li, Engle Abrams, Steve Yoon, Tianrui Yang, Yushu Huang, Michael Betenbaugh, Amanda Debes, Rosemary Morgan, Aaron Milstone, Andrew Karaba, Andrew Pekosz and Sabra Klein of Johns Hopkins and Steven Cramer and Andrew Kocot of Rensselaer Polytechnic Institute.

Ioannis Sitaras, Maggie Li, Camille Wouters, Steve Yoon and Andrew Pekosz received funding from the National Institute of Allergy and Infectious Diseases and the Centers for Disease Control and Prevention. Andrew Kocot, Steven Kramer and Michael Betenbaugh received grant support from the National Institute for Innovation in Manufacturing Biopharmaceuticals. Rosemary Morgan received funding from the National Institute on Aging and the National Institutes of Health. Aaron Milstone has received grants or contracts from the Agency for Healthcare Research and Quality, the Centers for Disease Control and Prevention, the National Institutes of Health and Merck. Andrew Karaba received National Institute of Allergy and Infectious Diseases funding and consulting fees from Roche. Sean Leng received National Institutes of Health grants, funding from Cybersecurity and Infrastructure Security Agency, Milstein Medical Asian American Partnership, the Sanofi grant project and the Howard and Abby Milstein Foundation, as well as honoraria for participating in the Sanofi COVID-19 Vaccine International Advisory Board, the Sanofi Speakers Bureau for Influenza Vaccines, and the GSK Speakers Bureau for Herpes Zoster Vaccine Shingrix. Sean Leng is also the president of the Milstein Medical Asian American Partnership foundation. Sabra Klein received support from the National Institute on Aging, National Cancer Institute and is a board member for the National Institutes of Health's Advisory Committee on Research on Women's Health and an editor for PloS Pathogens and the Journal of Virology. All other authors report no potential conflicts.

The research was funded by the National Institute on Aging -- National Institutes of Health, the National Cancer Institute, the National Institute of Allergy and Infectious Diseases, Johns Hopkins Center of Excellence in Influenza Research and Response, the Centers for Disease Control and Prevention, the Irma and Paul Milstein Program for Senior Health, the Milstein Medical Asian American Partnership Foundation, and the Howard and Abby Milstein Foundation, the collective community of donors to the Johns Hopkins University School of Medicine and the Johns Hopkins Health System, and the Fonds de Recherche du Québec-Santé.