| • We do not know how well HPV vaccination will protect
against cervical cancer. Trials have not focused on the
outcome of cervical cancer because they had too few
participants and did not follow them up for long enough:
cervical cancer may take decades to develop. |
| • Published numbers from randomised controlled trials may
overstate efficacy because: (a) testing occurred too
frequently in the trials when, in real-world settings,
lesions may regress spontaneously; (b) trials used composite
surrogate outcomes, some of which, such as HPV-infection and
CIN1, occur more frequently than others and are very
unlikely to progress to cancer; and (c) subgroups were
over-analysed. |
| • The trial populations have limited relevance and validity
for real world settings: for example, women in the trials
were older than the target population; we do not have enough
data on the benefits in women who may have been exposed to
HPV before they were vaccinated and who do not know their
HPV status. |
| • We do not have enough data on the impact of the vaccine on
CIN3, which is more likely than CIN1 and 2 to progress to
cervical cancer. We also have less data on the impact on
cervical disease due to any HPV type rather than just
lesions due to HPV 16 and 18. |
| • Women should still attend regular cervical screening
because efficacy in preventing cervical precursors is
<100% and there are more oncogenic types than those
covered by the vaccines. We have good evidence that cervical
screening significantly reduces the risk of cervical cancer
in women regardless of whether they have been vaccinated.
The number of new cancers and deaths has decreased markedly
such that cervical cancer now accounts for only 1% of cancer
deaths in women in the UK (854 deaths in 2016).1
|
| • Information from the trials can tell us what happens
between five and nine years after vaccination, but we do not
know if protection wanes after this time. |
| • A recent observational study provides some evidence of
efficacy against CIN3+ in girls vaccinated before sexual
debut. Ongoing observational studies may tell us about the
long-term effect on rates of cervical cancer, but it will
take many years before we have the evidence. |
