'Enhanced' Flu Vaccines Provide Better Protection for Elderly

As the push to boost flu vaccination rates rolls on, public health officials will put a particular emphasis on vulnerable groups such as the elderly and young children. Now, new research is shedding new empirical light on which vaccines might work best for the elderly.

Most people who receive a flu vaccine receive a trivalent or quadrivalent inactivated influenza vaccine, with 45 micrograms of hemagglutinin (HA) and 15 micrograms each of 2 influenza A strains and 1 or 2 influenza B strains.

Over the past decade, however, new “enhanced” versions of the flu vaccine have become available. Some early evidence has suggested that these stronger versions might better protect elderly patients against the flu, but scientific data has so far been relatively scant. In a new study in Clinical Infectious Diseases, a multinational team of investigators report on what they found when they directly compared standard-dose vaccines with 3 enhanced vaccines.

Corresponding author Benjamin J. Cowling, PhD, of Hong Kong University’s School of Public Health, noted that the elderly population is disproportionately affected by the flu.

“Influenza epidemics cause considerable health impact, and an average winter influenza season is responsible for 12,000-61,000 deaths and 140,000-810,000 hospitalizations in the US,” he said. “The majority of these occur in older adults, and this age group are a particular target for influenza vaccination campaigns.”

Cowling told Contagion® that because standard-dose flu vaccines tend to be merely “moderately” effective, it was important to understand whether enhanced vaccines would better protect this community.

“Each of the enhanced vaccines is thought to work better than standard dose vaccines in older adults, based on previous studies,” Cowling said. Our trial is the first large trial to provide direct comparisons between the vaccines.”

To study the question, Cowling and colleagues recruited approximately 1800 community-dwelling residents of Hong Kong between the ages of 65 and 82 years. None of the participants had already received a flu vaccination for the 2017-2018 flu season, the season first covered by the study. The enrollees were divided into 11 groups. (A large number of groups was necessary because the investigators plan to track participants over multiple years and examine different combinations of repeated vaccines.)

Three of the groups were given a standard-dose quadrivalent vaccine. Another 3 groups were given the trivalent MF59-adjuvanted vaccine, an enhanced vaccine that includes MF59, a squalene-based emulsion, and is marketed as Fluad. Another 3 groups were given a different enhanced vaccine, the trivalent FluZone, which has 4 times the standard amount of HA (180 micrograms). The final 2 groups received the recombinant HA-protein quadrivalent FluBlok, an enhanced vaccine that also contains 180 micrograms of HA.

Sera were collected from 200 patients who received each vaccine prior to vaccination and 30 days after vaccination. Analysis showed that all 3 enhanced vaccines led to stronger humoral and cell-mediated immune responses when compared to the standard-dose group. The findings were statistically strong with regard to the influenza A strains.

Cowling said he wasn’t surprised by the results, but he is eager to see what the continued research finds in future years.

“I am looking forward to subsequent years of this trial where we investigate repeat vaccination with enhanced vaccines,” he said.