A model built on Korean data says vaccinating boys clears Korea's cost-effectiveness threshold. The national programme still vaccinates girls only

Immunisation policy usually lags evidence, and the gap is normally argued over in general terms. In this case the argument has been made in Korean numbers, against the Korean programme, using Korea's own cost-effectiveness threshold — and published.

The comparison the model ran#

An established dynamic transmission model of HPV epidemiology was adapted to the South Korean population. It compared vaccinating girls and boys with the nonavalent vaccine against the programme currently administered, which vaccinates girls only with the quadrivalent vaccine.

Reductions of 4.8 to 8.2 percent were also projected in HPV-related vaginal, vulvar, anal and head and neck cancers in women.

Professional guidance has moved four times#

The Korean Society of Gynecologic Oncology first issued HPV vaccination guidelines tailored to Korea in 2016. It revised them in 2019 after the nonavalent vaccine became available, and again in 2021 to add recommendations for middle-aged women and men and for vaccination after conisation.

Its latest revision focuses on the necessity of vaccination in middle-aged men, states a position on the single-dose schedule the World Health Organization now recommends, addresses additional nonavalent vaccination for people previously given the bivalent or quadrivalent vaccine, and updates the evidence for two doses at ages 9 to 14.

Four revisions in a decade, each widening the recommended population, against a national programme whose scope has not changed, is the shape of an unresolved policy question rather than a settled one.

What the vaccine would not cover#

Among 44,065 Korean men tested for HPV between 2014 and 2022, overall positivity was 59.1 percent. HPV 6 was the most common low-risk type at 33.3 percent and HPV 11 next at 11.0 percent; HPV 16 dominated high-risk infection at 5.2 percent. Just under half of positive men — 49.3 percent — carried more than one genotype.

High-risk genotypes outside the nonavalent vaccine's nine types, principally HPV 53, 51, 39 and 66, accounted for between 27.6 and 35.0 percent of infections annually. The authors of that study conclude the data supports including males in national vaccination strategies with the current nonavalent vaccine, and that genotype surveillance needs to continue.

What this does not establish#

1. A model is a projection under assumptions, not a measurement. Its outputs depend on the transmission parameters, coverage assumptions and time horizon chosen, and a 100-year horizon accumulates benefit that a shorter one would not.
2. The cost-effectiveness ratio applies to a combined change of vaccine and target population and cannot be read as the incremental cost of adding boys alone.
3. Cost-effectiveness is one input to immunisation policy. Budget impact, vaccine supply, delivery capacity and competing programmes are others, and none of them appear in this figure.
4. Six of the seven authors are employed by the vaccine manufacturer. That does not make the model wrong, and it does mean the assumptions were chosen by a party with an interest in the result.
5. The genotype study covers men who presented for HPV testing, a group already more likely to be positive than the general population.
6. None of this describes what an individual should do, which is a separate question this publication covers separately.

What is on the record is that the case for vaccinating Korean men has been modelled on Korean data, cleared the threshold Korea uses to judge such things, and been echoed by the relevant professional society across four revisions — and that the national programme, as the model itself describes it, still vaccinates girls only.