RSV can be fatal for vulnerable people
The findings, published in The Lancet Infectious Diseases, come from a target trial emulation study led by researchers at the Veterans Affairs Portland Health Care System in Oregon. The observational study was designed to fill in knowledge gaps remaining after clinical trials (e.g., vaccine effectiveness (VE) in people with weakened immune systems, effects on healthcare use for infection).
Vaccine uptake low
The researchers used electronic health records at the
Veterans Health Administration (VHA) to emulate a target trial comparing a
single dose of RSV vaccine (RSVPreF3 [Arexvy] or RSVpreF [Abrysvo]) with no
vaccination in veterans aged 60 years and older from September through December
2023, with follow-up until March 2024.
By the end of the 2023–24 respiratory illness season,
only 24% of eligible adults in the USA had received an RSV vaccine.
The 146,852 vaccine recipients were matched with as many as four unvaccinated controls (582,936 total) in four monthly nested sequential trials. Of all participants, 94.0% were men, and the median age was 75.9 years. A total of 41.5% of participants had cardiovascular disease, 30.2% had chronic lung disease, and 5.2% had weakened immune systems. Of all vaccinees, 69.2% received Abrysvo, and 29.9% received Arexvy.
"In June, 2023, the Advisory Committee on Immunization
Practices recommended a single dose of RSV vaccine in adults aged 60 years and
older, using shared clinical decision making," the study authors noted.
"By the end of the 2023–24 respiratory illness season, only 24% of
eligible adults in the USA had received an RSV vaccine."
Findings support current recommendations
Estimated VE was 78.1% (95% confidence interval [CI], 72.6%
to 83.5%) against RSV infection, 78.7% (95% CI, 72.2% to 84.8%) against
RSV-related ED/UC visits, and 80.3% (65.8% to 90.1%) against hospital
admission.
Among high-risk subgroups, estimated VE against RSV
infection was 72.3% (57.9% to 84.6%) in veterans aged 80 years and older and
71.6% (55.4% to 85.2%) in those with weakened immune systems.
During a median follow-up of 124 days, the incidence of RSV
infection was 1.7 events per 1,000 person-years (88 total infections) among
vaccinated participants and 7.3 per 1,000 person-years (372 infections) among
the unvaccinated.
Extended follow-up over subsequent respiratory illness
seasons is needed to assess the duration of the protective effect of
vaccination.
In total, there were 66 ED/UC visits (1.3 per 1,000
person-years) in the vaccinated group and 289.3 (5.7 per 1,000 person-years) in
the unvaccinated group. There were 15 hospitalizations (0.3 per 1,000
person-years) and 80.3 (1.6 per 1,000 person-years) in the vaccinated and
unvaccinated groups, respectively.
There were no intensive care unit (ICU) admissions in the
vaccinated group and 0.2 per 1,000 person-years among the unvaccinated. No
vaccinated participants died, versus 0.1 per 1,000 person-years in unvaccinated
participants.
The rates of RSV infections from day 14 among unvaccinated
and vaccinated groups, respectively, were highest among those with weakened
immune systems (19.9 vs 5.8 events per 1,000 person-years) and those
with the highest VHA Care Assessment Need scores (16.1 vs 4.0 events
per 1,000 person-years).
"These findings support current recommendations for RSV
vaccination among individuals aged 60 years and older," the researchers
wrote. "Extended follow-up over subsequent respiratory illness seasons is
needed to assess the duration of the protective effect of vaccination."
Several questions remain
In a related commentary,
Harish Nair, MBBS, PhD, and Thomas Williams, MB BChir, both of the University
of Edinburgh, cautioned that veterans are not representative of the United
States as a whole.
"Moreover, the median follow-up was only 4.1 months,
compared with data from over two seasons available from the vaccine
trials," they wrote. "Therefore, several questions that were
unanswered by the RSV vaccine RCTs remain, and new questions have arisen."
More research is needed to determine the optimal RSV
vaccination schedule, VE in women in a real-world setting, and VE against
post-RSV ICU admissions, complications, and death, "all of which are
likely to feed into the cost-effectiveness models that are needed to inform
expanding RSV vaccination to broader age groups," Nair and Williams wrote.
"It is likely that several more such studies will need
to be conducted using diverse databases over a range of geographies in the next
few years to answer these questions and guide immunisation policies," they
concluded.
