Few vertical HIV transmissions in the UK but contributing factors remain associated with inequality

Polly Clayden, HIV i-Base

Vertical HIV transmission is rare in the UK, occurring mainly among undiagnosed women and often reflecting poor social circumstances – according to surveillance data presented at the 5th Joint Conference of the British HIV Association (BHIVA) with the British Association for Sexual Health and HIV (BASHH).

The UK vertical transmission rate has been below 0.3% since 2012. Despite very high uptake of antenatal screening, a small number of vertical transmissions still occur.

These transmissions are monitored by the Integrated Screening Outcomes Surveillance Service (ISOSS), part of Public Health England’s Infectious Diseases in Pregnancy Screening programme. ISOSS performs the following:

  • Conducts active surveillance of all pregnancies to women living with HIV, their infants and any children diagnosed with HIV at less than 16 years of age.
  • Conducts enhanced data collection of vertical transmissions in children born since 2006.
  • Collects supplementary maternal and infant information through interviews with paediatric, maternity and HIV clinicians involved in each case.
  • Establishes circumstances surrounding transmissions and any contributing factors through a Clinical Expert Review Panel (CERP).

A poster presentation at the conference described the latest findings on vertical transmissions from a review of cases reported between January 2014 and December 2019.

There were 35 vertical transmissions in infants born to 33 mothers (including 1 set of siblings and 1 pair of twins). Years of birth ranged from 2006 to 2019 and infant age at diagnosis from birth to 11 years.

The CERP identified the main factors contributing to transmission – in some cases there were overlapping and multiple factors.

Two thirds of children were born to women diagnosed after pregnancy: 24 (69%) after, 4 (11%) during and 7 (20%) before pregnancy.

Almost half were born in London: 15 (43%), 7 (20%) Midlands and east England, 6 (17%) north England, 3 (9%) south England and 4 (11%) Wales and Scotland.

The median maternal age at delivery was 33 years (IQR 28 to  36). Three quarters of mothers were born in sub-Saharan Africa: 26 (74%), 3 (9%) Eastern Europe and 6 (17%) UK.

Over half the mothers (54%) reported adverse social circumstances: 5 safe guarding, 9 mental health, 7 housing, 3 drug/alcohol use, 5 intimate partner violence, 5 uncertain immigration status, 4 financial issues and 7 English language issues.

Of the 24 women diagnosed after pregnancy, 16 tested negative in pregnancy and seroconverted during pregnancy or breastfeeding. Some reported new or multiple partners during pregnancy. And some women had partners who did not disclose their HIV status and partners who died of HIV related symptoms.    

There were 5 transmissions among women who declined HIV testing, all occurring before 2010 – the authors noted that these women accepted all other infectious disease tests. One woman declined testing in two pregnancies and both children were diagnosed with HIV.

Among the 11 women who were diagnosed before or during pregnancy, in 5 cases transmission was post-natal and likely due to non-disclosure of breastfeeding. These women had complicating factors including mental health issues and involvement by social services. Some women also had difficulties with engagement with health care services.


This ongoing enhanced data collection provides valuable insights into the circumstances behind the few vertical transmissions still occurring in the UK. ISOSS can also provide data on evolving patterns in this group, including maternal demographics, to inform work to address their needs.

Presenting author, Helen Peters explained that although exact dates for vertical transmissions were not included the majority occurred in the earlier period of this surveillance and there has been a decline over the years.

But the issues identified here support findings from previous reviews highlighting that social circumstances associated with inequality still drive the small numbers of vertical HIV transmissions that remain in the UK.       


Peters HP et al. Vertical transmissions in the UK- insights and remaining challenges. 5th Joint Conference of the British HIV Association (BHIVA) with the British Association for Sexual Health and HIV (BASHH). 19–21 April 2021. Poster abstract P027. (abstract book) (webcast – Themed poster discussion: ongoing challenges)

This report was first published on 15 June 2021.

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