  Background: After a decade of a treatment as prevention (TasP) strategy based
on progressive HIV testing scale-up and earlier treatment, a reduction in the
estimated number of new infections in men-who-have-sex-with-men (MSM) in
England had yet to be identified by 2010. To achieve internationally agreed
targets for HIV control and elimination, test-and-treat prevention efforts have
been dramatically intensified over the period 2010-2015, and, from 2016,
further strengthened by pre-exposure prophylaxis (PrEP).
  Methods: Application of a novel age-stratified back-calculation approach to
data on new HIV diagnoses and CD4 count-at-diagnosis, enabled age-specific
estimation of HIV incidence, undiagnosed infections and mean time-to-diagnosis
across both the 2010-2015 and 2016-2018 periods. Estimated incidence trends
were then extrapolated, to quantify the likelihood of achieving HIV elimination
by 2030.
  Findings: A fall in HIV incidence in MSM is estimated to have started in
2012/3, eighteen months before the observed fall in new diagnoses. A steep
decrease from 2,770 annual infections (95% credible interval 2.490-3,040) in
2013 to 1,740 (1,500-2,010) in 2015 is estimated, followed by steady decline
from 2016, reaching 854 (441-1,540) infections in 2018. A decline is
consistently estimated in all age groups, with a fall particularly marked in
the 24-35 age group, and slowest in the 45+ group. Comparable declines are
estimated in the number of undiagnosed infections.
  Interpretation: The peak and subsequent sharp decline in HIV incidence
occurred prior to the phase-in of PrEP. Definining elimination as a public
health threat to be < 50 new infections (1.1 infections per 10,000 at risk),
40% of incidence projections hit this threshold by 2030. In practice, targeted
policies will be required, particularly among the 45+y where STIs are
increasing most rapidly.
