Previous Seasons' Flu Shots Protective, Less So for Elders

By Reuters Staff

June 07, 2019

NEW YORK (Reuters Health) - Influenza vaccines given in previous seasons still provide some protection against infection, according to a new study.

The protective effects weren't as long-lasting in elders and chronically ill patients, however, Dr. Jesus Castilla of the Instituto de Salud Publica de Navarra in Pamplona, Spain, and colleagues found.

Public health officials in Navarra have conducted annual vaccine effectiveness (VE) studies since 2009, the authors note in the Journal of Infectious Diseases, online May 20. They reviewed VE data from seven influenza seasons for nearly 9,000 swabbed patients, including 4,124 from primary care settings and 4,809 from hospitalized patients.

Influenza was confirmed in 61% of the primary-care patients and 35% of the hospitalized patients.

Based on the last influenza vaccine dose a person had received, VE was 40% for the current season, 42% for the previous season, 35% for the second and third previous seasons, and 31% for the fourth and fifth previous seasons, Dr. Castilla and his team found.

Current-season vaccination was 41% effective for preventing consultations with primary healthcare in which influenza was confirmed, and effectiveness was similar for vaccines received up to four to five seasons previously.

Current-season VE and previous season VE were 40% and 43%, respectively, but VE was lower for the third, fourth and fifth previous seasons.

The more doses a person had received in the past, the stronger the protective effect. In several analyses, VE for people who had received at least three previous doses or had their last shot in the previous season was similar to VE for the current season.

"In healthy young people the residual effect of prior vaccinations was long-lasting and showed a similar magnitude to the effect of current season vaccination," Dr. Castilla and colleagues write. "In the elderly and chronic patients the residual effect of prior vaccines declined with the time since the last dose, and having received more than one dose of vaccine seemed important to achieve a long-lasting residual effect."


J Infect Dis 2019.