Discuss the safety and use of vaccines in pregnancy

Clinical overview

Vaccination in pregnancy is one of the highest-yield, lowest-cost interventions in the entire antenatal package, yet it is repeatedly missed at booking and underused in South African clinics. The logic is deceptively simple: the pregnant woman is herself more vulnerable to several infections (influenza, COVID-19, varicella, hepatitis E), and her newborn — who cannot mount a protective response to most pathogens for weeks to months — depends entirely on antibody transferred across the placenta before birth. Maternal immunisation is therefore a two-patient intervention: we protect the mother during a uniquely immunologically and physiologically altered state, and we protect the infant during the dangerous window before the infant's own primary vaccine series takes effect.

The registrar must hold two ideas in tension. First, the dominant principle is that inactivated vaccines, toxoids and most subunit/recombinant vaccines are safe at any stage of pregnancy and should be given when indicated — there is no plausible mechanism by which a non-replicating antigen harms the fetus, and decades of surveillance support this. Second, live attenuated vaccines are generally contraindicated because of a theoretical risk of transplacental fetal infection, although inadvertent administration has not been shown to cause fetal harm and is never on its own an indication for termination. Getting this dichotomy right — and being able to defend it from mechanism — is the examinable core of this objective. South African practice layers two further realities on top: a high background HIV prevalence that modifies both vaccine response and indication, and a vaccine schedule and access that differ from European or American guidance. This chapter discusses the safety, the mechanisms and the practical SA use, weighting the discussion as the HOTS verb "discuss" demands.

Core knowledge

The immunological rationale

Two physiological facts drive maternal immunisation. The first is transplacental IgG transfer. Maternal IgG (predominantly IgG1) is actively transported across the syncytiotrophoblast by the neonatal Fc receptor (FcRn), a process that accelerates markedly in the third trimester. Transfer is most efficient after roughly 32–34 weeks, which is why the timing of certain vaccines (notably tetanus-containing and any pertussis-containing vaccine) is chosen to maximise the antibody pool available for transfer before delivery. Vaccinating too late leaves insufficient time for maternal seroconversion and transfer; vaccinating very early may mean antibody titres have waned by term. The second fact is the relative immunomodulation of pregnancy — a shift that increases susceptibility to severe disease from influenza and varicella in particular, justifying maternal protection in its own right.

Figure I9.1 — Transplacental IgG transfer via FcRn and the timing logic for transfer-dependent maternal vaccines.

Classifying vaccines by safety in pregnancy

The single most important framework is the live-versus-non-live distinction.

The reason for caution with live vaccines is the theoretical possibility that an attenuated replicating organism crosses the placenta and infects the fetus. It is crucial to be precise: this is a theoretical/precautionary concern. Inadvertent administration of MMR, varicella or even yellow-fever vaccine in early pregnancy has not been associated with the congenital syndromes caused by the wild-type infections, and inadvertent vaccination is not an indication for termination of pregnancy — see termination-of-pregnancy. This nuance is a classic exam discriminator.

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Figure I9.2 — The live-versus-non-live vaccine safety framework, including postpartum deferral and yellow-fever exceptions.

Tetanus — the SA backbone

Maternal and neonatal tetanus elimination rests almost entirely on maternal immunisation, and tetanus toxoid (or Td) is the foundational antenatal vaccine in South African practice, recommended through the NDoH Maternity Care Guideline. Neonatal tetanus follows contamination of the umbilical stump in a baby born to an unprotected mother; maternal tetanus follows septic abortion or unhygienic delivery. Both are entirely preventable by ensuring protective maternal antibody that transfers to the infant. The classically taught primary course is a series of doses (standard teaching: a primary series of multiple TT/Td doses with subsequent boosters conferring long-lasting protection), with the antenatal dose timed so transfer is maximal before delivery. The exact dosing schedule and number of doses should be confirmed against the current NDoH Maternity Care Guideline and the SA EML rather than recalled from memory.

Influenza — severe disease prevention

Pregnant women have a substantially elevated risk of severe influenza, including hospitalisation, pneumonia and death, particularly in the second and third trimesters and the early postpartum period. Inactivated influenza vaccine is recommended in pregnancy at any gestation and is endorsed by WHO as a priority group. It protects the mother from severe disease and the infant in the first months of life through transferred antibody — the only way to protect infants too young to be vaccinated. The intranasal live attenuated influenza vaccine (LAIV) is contraindicated; only the inactivated injectable form is used.

Pertussis (whooping cough)

Maternal pertussis (acellular) vaccination — given as a combined Tdap-type product in the third trimester in many international programmes — protects the young infant during the lethal window before primary immunisation. The mechanism is again transplacental antibody, hence third-trimester timing. South Africa has historically not run a universal antenatal pertussis programme to the same extent as the UK, so the registrar should state pertussis vaccination's strong rationale and international use but check current local availability and NDoH recommendation rather than assert it as routine SA practice — this is flagged as a point where SA practice may diverge from international guidance.

COVID-19

Pregnancy is a recognised risk factor for severe COVID-19, and maternal vaccination (mRNA or protein-subunit platforms — both non-live) has been used in pregnancy at any gestation with reassuring safety data and the added benefit of transplacental antibody. It remains recommended for pregnant women per WHO and SA guidance during periods of relevant circulation; confirm the current local recommendation, which changes with the epidemiology.

Vaccines for specific exposures

• Hepatitis B (recombinant, non-live): safe in pregnancy; give to non-immune women at risk. The separate but critical issue of preventing vertical transmission at birth (birth-dose vaccine ± hepatitis B immunoglobulin for infants of HBsAg-positive mothers) is part of the booking and newborn pathway.
• Rabies (inactivated, plus immunoglobulin): post-exposure prophylaxis is never withheld in pregnancy — untreated rabies is uniformly fatal, so the risk-benefit is absolute.
• Tetanus immunoglobulin and other immunoglobulins: passive immunisation is safe and used as indicated (e.g. wound management, varicella exposure in a susceptible woman, hepatitis B exposure).

Assessment

A structured immunisation assessment belongs in every booking visit. Link this to antenatal-booking and the broader SA Maternity Guideline workflow.

History and risk stratification

• Tetanus status: number and timing of prior TT/Td doses, prior pregnancies' vaccination, and any high-risk wounds. An undocumented or incomplete history is treated as non-immune.
• Immunity to rubella and varicella: ask about prior infection or vaccination and document; if susceptible, the plan is postpartum MMR/varicella (these are live and deferred), with counselling to avoid exposure during pregnancy.
• Influenza and COVID-19: prior vaccination this season; intention to vaccinate.
• Hepatitis B: serostatus (HBsAg), risk factors, and the infant pathway if positive.
• Travel: planned travel to yellow-fever or other endemic areas — see travel-in-pregnancy — which may force a difficult live-vaccine decision.
• HIV status and immune state: HIV is highly prevalent in the SA antenatal population (see hiv-in-pregnancy and hiv-counselling). HIV alters both vaccine response (lower seroconversion with low CD4) and safety (live vaccines are contraindicated in severe immunosuppression independent of pregnancy). Document CD4/viral load context.
• Allergy and prior reactions: anaphylaxis to a previous dose or a vaccine component is a contraindication to that vaccine.

Examination and investigations

Examination is generally unremarkable; check for acute febrile illness (a temporary reason to defer until recovered, not a true contraindication). Serology (rubella IgG, varicella IgG, HBsAg) may guide postpartum planning and infant protection. There is no routine antibody-titre check before giving tetanus or influenza vaccine — the decision is clinical and history-based.

Management

General principles

1. Give all indicated inactivated/toxoid/subunit vaccines when due — there is no gestational age at which a non-live vaccine is "too risky"; the dominant error in practice is omission, not over-vaccination.
2. Defer all live attenuated vaccines to the postpartum period. MMR and varicella are ideally given before discharge after delivery (breastfeeding is not a contraindication to MMR or varicella). Advise effective contraception for the recommended interval after a live vaccine if it is given pre-conception — see contraceptive-modalities.
3. Time transfer-dependent vaccines correctly. Tetanus-containing (and any pertussis-containing) vaccine is timed so that maternal seroconversion plus transplacental transfer maximises the infant's antibody at birth — favouring the late second to third trimester for the transfer benefit, while the maternal-protection benefit of influenza/COVID applies at any gestation.
4. Co-administration of non-live vaccines is generally acceptable; document each.

The South African practical pathway

• Tetanus/Td: the routine antenatal backbone per the NDoH Maternity Care Guideline and the SA EML; ensure every pregnant woman is brought up to a protective status. Confirm the exact dose count and timing against the current guideline.
• Influenza (inactivated): offer to all pregnant women, prioritised by WHO; align with national seasonal supply.
• COVID-19 (non-live): per the prevailing national recommendation for the circulating epidemiology.
• Hepatitis B: non-immune at-risk women; ensure the infant birth-dose pathway for HBsAg-positive mothers is in place.
• HIV-positive women: give inactivated/toxoid vaccines as indicated (response may be lower with advanced immunosuppression — ensure ART per the HIV-in-pregnancy pathway and the SA HIV/ART guidelines); avoid live vaccines in severe immunosuppression, and weigh CD4 even for postpartum live vaccines.
• Levels of care: routine maternal immunisation is a primary-care / district function delivered at booking and antenatal visits; complex decisions (severe immunosuppression, unavoidable yellow-fever travel, post-exposure dilemmas) warrant regional/tertiary or infectious-diseases input.

Yellow fever and unavoidable travel

Yellow-fever vaccine is live attenuated and is avoided in pregnancy. If travel to a high-transmission endemic area is genuinely unavoidable, the decision becomes a risk-benefit judgement: the risk of severe wild-type yellow fever may exceed the theoretical vaccine risk, in which case vaccination can be offered with documented counselling — see travel-in-pregnancy. A waiver letter, rather than vaccination, may suffice for purely entry-requirement (rather than true-exposure) situations. Escalate these decisions.

Emergency: post-exposure prophylaxis and anaphylaxis

Two situations are unmistakable and must be drilled.

RABIES post-exposure prophylaxis is NEVER withheld in pregnancy. Rabies is essentially 100% fatal once symptomatic. After a high-risk animal exposure: wash the wound thoroughly, give rabies vaccine (inactivated — safe) AND rabies immunoglobulin per protocol, and update tetanus. Pregnancy does not modify the regimen. Do not delay to "think about it."

ANAPHYLAXIS to a vaccine is a resuscitation emergency. Recognise: rapid-onset airway/breathing/circulation compromise with urticaria/angioedema after the dose.

• Call for help; ABC.
• Adrenaline (epinephrine) IM into the anterolateral thigh, repeated every ~5 minutes as needed — the first-line, time-critical drug (confirm the weight/age-appropriate IM dose against the current resuscitation protocol).
• High-flow oxygen; lie flat with legs raised (left-lateral tilt if late pregnancy to relieve aortocaval compression); IV fluids for hypotension.
• Adjuncts (antihistamine, steroid) are second-line and never delay adrenaline.
• Monitor for biphasic reaction; document and report the adverse event.

Every site giving vaccines must have an anaphylaxis kit and a trained responder. The maternal-collapse principles in resuscitation-in-pregnancy apply if cardiac arrest supervenes.

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Figure I9.3 — Practical antenatal vaccine pathway with rabies post-exposure prophylaxis and anaphylaxis response drills.

Red flags / pitfalls

• Withholding a needed inactivated vaccine "to be safe." The commonest and most harmful error. Influenza, tetanus, hepatitis B and COVID-19 vaccines are safe and indicated — omission leaves mother and infant unprotected.
• Treating inadvertent live-vaccine administration as a catastrophe. Accidental MMR, varicella or yellow-fever vaccine in early pregnancy is not an indication for termination; counsel, reassure, document, and offer routine surveillance. Reflexive referral for termination-of-pregnancy on this basis is wrong.
• Giving a live vaccine in pregnancy. Conversely, never electively give MMR, varicella, LAIV, OPV, BCG, oral typhoid or yellow fever to a known pregnant woman.
• Mistiming transfer-dependent vaccines. Giving tetanus/pertussis-containing vaccine too late leaves no time for seroconversion plus transfer; very early dosing risks waned titres at term.
• Ignoring HIV. Failing to account for immunosuppression — both lower vaccine response and the contraindication to live vaccines in severe immunosuppression — in a high-prevalence population. Confirm ART and CD4 context.
• Forgetting passive immunisation. Immunoglobulins (rabies, tetanus, hepatitis B, varicella-zoster) are safe and sometimes the key intervention for an exposed susceptible woman.
• Deferring rabies PEP. A potentially fatal mistake; PEP is never withheld for pregnancy.
• Failing to document. Vaccine, batch, site, date and counselling must be recorded — both for continuity and adverse-event reporting.
• Acute moderate-to-severe febrile illness: a reason to defer (not permanently contraindicate) until recovery; a mild illness without significant fever is not a reason to defer.

Evidence anchors

• National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024), NDoH — the South African source of truth for routine antenatal tetanus immunisation and the booking immunisation assessment; confirm exact dosing/timing against the current PDF.
• South African EML — Hospital and Primary Care levels — for tetanus toxoid/Td and other vaccine availability and the standard dosing/schedule.
• South African National HIV/ART Consolidated Guidelines (2023) and 2023 SAHCS Adult ART Guidelines — relevant to immunisation in the HIV-positive pregnant woman (vaccine response, live-vaccine caution in immunosuppression, ART optimisation).
• WHO position papers and immunisation guidance — prioritisation of inactivated influenza vaccine in pregnancy, maternal/neonatal tetanus elimination strategy, and pertussis programme rationale (general WHO immunisation canon; verify the specific position paper edition before quoting figures).
• NICE NG201 — Antenatal care (2021) — booking-visit structure within which immunisation assessment sits.
• Choice on Termination of Pregnancy Act 92 of 1996 — relevant only to refute the misconception that inadvertent live-vaccine exposure warrants termination; it does not.

Notes on hedged/standard-textbook content: the live-vs-non-live safety dichotomy, the FcRn/transplacental-IgG transfer mechanism and timing logic, third-trimester transfer optimisation, the specific list of live vaccines, and the anaphylaxis/rabies-PEP drills are standard immunology/clinical canon stated cautiously here rather than line-cited; exact tetanus dose counts, pertussis-programme local availability, and seasonal COVID-19 recommendations must be confirmed against the current NDoH Maternity Care Guideline, SA EML and prevailing national directives before being asserted as numbers.