Silent Transmission Gap’ in Mother-to-Child HIV Transmission

Context

Mother-to-child transmission (MTCT) of HIV remains a major barrier to eliminating HIV in children. Some babies acquire HIV despite mothers testing HIV-negative during pregnancy.

What is Mother-to-Child Transmission (MTCT) of HIV?

1. Definition: Transmission of HIV from an infected mother to her baby:
   1. During pregnancy (intra-uterine),
   2. During delivery (exposure to maternal blood and genital secretions),
   3. During breastfeeding (virus in breast milk).
2. Prevention so far (broad idea):
   1. Early antenatal HIV testing for pregnant women.
   2. Antiretroviral therapy (ART) for HIV-positive mothers to suppress viral load.
   3. Prophylactic medicines for newborns.
   4. Safer delivery practices and counselling on breastfeeding options.
3. These steps have reduced MTCT significantly, but do not fully protect against cases where the mother becomes infected after the first negative test.

What is the ‘Silent Transmission Gap’?

1. The silent transmission gap refers to HIV infection in infants born to mothers who tested HIV-negative earlier in pregnancy, but:
   1. acquired HIV later in pregnancy or during breastfeeding, or
   2. were in the window period when the test was done (infection present, but not yet detectable).
2. The gap arises because:
   1. Most programmes do only one HIV test early in pregnancy,
   2. There is no routine repeat testing in late pregnancy, at delivery, or during breastfeeding,
   3. New infections and window period infections are missed, so:
      1. the mother is not put on ART,
      2. the baby does not receive proper prophylaxis,

• transmission risk remains high.

Why does this gap occur?

1. New HIV infection during pregnancy or breastfeeding
   1. A woman may be HIV-negative in early pregnancy, but:
      1. get infected later via unprotected sex, or
      2. exposure to infected blood/products, etc.
   2. The newly acquired infection has a very high viral load, which greatly increases risk of MTCT.
   3. If no second test is done, this new infection is never detected, and neither mother nor baby receives timely treatment.
2. The ‘Window Period’ of HIV infection
   1. After someone acquires HIV, there is a window period when:
      1. the virus is present,
      2. but standard antibody-based screening tests may still show negative.
   2. During this period:
      1. Transmission risk is high, as viral load is very high.
      2. A pregnant woman may test negative, but still be capable of transmitting HIV to the baby.
   3. One-time testing approach
      1. In many settings, only one HIV test in early pregnancy is routinely done.
      2. Without repeat testing in:
         1. late pregnancy,
         2. at delivery,

• during breastfeeding,
  new infections and window-period infections are not caught.

4. Timing of infection and high-risk periods
   1. Risk is especially high when the mother acquires HIV in late pregnancy, around delivery, or during breastfeeding because:
      1. there is no time to start effective ART before exposure,
      2. baby is directly exposed to high viral load during birth and breastfeeding.

How can this be prevented?

1. For Pregnant and Breastfeeding Women
   1. Repeat HIV Testing
      1. Late pregnancy: A second test in the third trimester.
      2. At delivery: Testing at labour/admission.

• During breastfeeding: Periodic testing, especially in high-prevalence or high-risk settings.

1. Targeted additional testing
   1. Extra tests for women who:
      1. report recent high-risk exposure,
      2. have symptoms suggestive of acute infection,
      3. have HIV-positive partners or partners of unknown status.
   2. Counselling and partner involvement
      1. Condom use, partner testing, and awareness about the window period.
      2. Counselling about continuing risk even after one negative test.
   3. For Infants
      1. Early virologic testing
         1. Use of virologic tests (e.g. PCR) rather than antibody tests,
         2. Soon after birth, and

• Repeat testing as per protocol, especially if mother seroconverts later.

1. Prompt treatment
   1. If infant test is positive: Immediate initiation of ART to reduce disease progression and improve survival.

Implications

1. Public Health & Programme Design
   1. Current PPTCT (Prevention of Parent-to-Child Transmission) strategies are not enough if they rely on a single antenatal test.
   2. Guidelines need explicit provisions for repeat testing and infant virologic testing.
2. Health Systems Strengthening
   1. Requires:
      1. more testing kits,
      2. trained staff,

• lab capacity for virologic tests,

1. tracking systems for mother–baby pairs.

3. Women’s and Child Rights
   1. Children born with HIV due to missed testing represent a preventable failure.
   2. Ethical imperative to ensure that all pregnant and breastfeeding women have repeated, accessible testing.
4. SDGs and National Targets
   1. India’s and global goals to eliminate paediatric HIV cannot be met unless this silent gap is addressed.

Challenges & Way Forward

Conclusion

Preventing paediatric HIV now depends less on new drugs and more on better timing and repetition of testing. If health systems ensure repeat maternal testing, early infant diagnosis and prompt treatment, this silent transmission gap can be closed. Doing so is essential for any credible effort to eliminate HIV in children.