Cancer risk reduced by 80% when kids under 16 are vaccinated
The reviews span both randomized controlled trials (RCTs)
and large population-level studies, drawing on data from more than 132 million
people.
80% reduction in cervical cancer
A population-level analysis included
225 studies from 46 countries and found an 80% reduction in cervical cancer
among girls vaccinated by age 16 (risk ratio [RR], 0.20). Risk reductions were
smaller among those vaccinated later in adolescence or in adulthood.
The review also reported moderate-certainty evidence that
vaccination lowers rates of precancerous cervical lesions and the incidence of
anogenital warts.
The review also found no evidence linking HPV vaccination to
widely discussed harms, including infertility, chronic fatigue syndrome (also
known as myalgic encephalomyelitis), Guillain-Barre syndrome, and complex
regional pain syndrome.
A separate analysis of
RCTs evaluated four HPV vaccines approved by the World Health Organization
(WHO)—Cervarix, Gardasil, Gardasil-9, and Cecolin—across 60 trials including
157,414 participants.
While the trials did not last long enough for cancers to
develop, the vaccines reduced high-grade vaccine-matched precancerous cervical
lesions 60% (RR, 0.40) in females ages 15 to 25 after six years. A pairwise
analysis of 39 studies showed that rates of serious adverse events did not
differ between the vaccine and control groups (RR, 0.99) at up to 72 months
follow-up.
Geographic gaps, need for longer-term research
The two reviews “provide the most comprehensive and
up-to-date evidence on HPV vaccination to date,” notes a Cochrane press release.
Still, the authors highlight some evidence gaps and limitations. Most of the
research was conducted in high-income countries, so more research is needed in
lower- and middle-income countries where cervical cancer screening programs are
lacking. The researchers also call for more long-term studies.
“Longer-term data will continue to strengthen our
understanding of how HPV vaccination protects against cancer over a lifetime,”
senior author Jo Morrison, DPhil, gynecologic oncology consultant at Somerset
NHS Foundation Trust and honorary associate professor at the University of
Exeter, says in the release. “Whilst we now have sufficient data to see a
beneficial effect of HPV vaccination on cervical cancers, which tend to develop
in younger women, it will take decades to fully understand the impact of vaccination
on vulval, peri-anal, penile and head and neck cancers, which often develop
later in life.”
