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Undetectable viral load at time of immunisation enhances yellow fever vaccine protection for people with HIV
Michael Carter, 2017-11-24 07:50:00
at the time of immunisation is the most important determinant of long-term
response to yellow fever vaccination among people with HIV, Swiss
investigators report in Clinical
Infectious Diseases. Every person
with an undetectable viral load at the time of first yellow fever vaccination
continued to have a protective response ten years after vaccination, they found.
with HIV demonstrated good short-term immune response to YFV [yellow fever
vaccination], which decreased to 75% ten years p.v. [post vaccination,” comment
the authors. “The long-term immune response of patients with HIV RNA suppressed
at vaccination remained unimpaired for up to ten years.”
believe their findings have implications for vaccination strategies, writing:
“HIV-infected patients mount a long-standing protective immune response to YFV
up to at least ten years if they are vaccinated while remaining on successful
cART [combination antiretroviral therapy]…until further data are available a
single booster after ten years seems to be adequate to restimulate the vaccine
response in the event of new travel to a YF [yellow fever] endemic area.”
Yellow fever is a
mosquito-borne severe viral haemorrhagic disease. There is no antiviral
treatment. However, there is a highly effective vaccine. The World Health
Organization issued guidance in 2013 recommending that individuals should
receive yellow fever vaccination boosters every ten years to obtain life-long
protection against the disease.
Many HIV-positive individuals
live in or travel to areas where yellow fever is endemic. The long-term
response to yellow fever vaccination in patients with HIV is poorly understood.
Investigators from the Swiss HIV Cohort Study therefore identified 247 patients
with a documented first yellow fever vaccination after their diagnosis with
HIV. Stored blood samples were examined to see if patients had an immune
response at one, five and ten years post-vaccination. A yellow fever plaque
reduction neutralisation titre (PRNT) of 1: >10 was regarded as
reactive and protective. Predictors of vaccine response were also examined.
The majority of
patients were from sub-Saharan Africa. Most (82%) were taking cART at baseline
and 83% had an undetectable viral load (below 400 copies/ml). Median CD4 cell
count was 536 cells/mm3.
vaccination is only recommended for asymptomatic HIV-positive patients with a
CD4 cell count above 200 cells/mm3. This is because it is a
live-attenuated vaccine and therefore poses significant health risk for
patients with very weak immune systems. Despite this recommendation, the
investigators identified eleven individuals who were immunised against yellow
fever while their CD4 cell count was dangerously low.
Overall, PRNT was
reactive in 46% of patients before vaccination. A protective immune response
was present one, five and ten years post-vaccination in 95%, 86% and 75% of
In patients with
suppressed viral load at the time of immunisation, the proportion with reactive
PRNT remained consistently high: 99% at year one, 99% at year five and 100% at
viral load at the time of vaccination was the single biggest determinant of
long-term response to the vaccine.
The authors recommend
that patients with HIV should be vaccinated against yellow fever once their
viral load is suppressed and that they should receive a booster after ten years
if they remain on suppressive cART. However, patients who were vaccinated while
their viral load was detectable should either have their immune response to the
vaccine measured or receive a booster vaccination, irrespective of the time
since first yellow fever vaccination.