Can a pregnant patient safely receive a single 0.5 mL intramuscular dose of Influvac Tetra (inactivated quadrivalent influenza vaccine), and what are the contraindications?

Influenza Vaccination in Pregnancy: Safety and Recommendations

Yes, pregnant patients can and should safely receive a single 0.5 mL intramuscular dose of Influvac Tetra (inactivated quadrivalent influenza vaccine) during any trimester of pregnancy, with the only absolute contraindication being a severe allergic reaction to a previous dose or vaccine component.

Safety Profile

Inactivated quadrivalent influenza vaccines are extensively validated as safe throughout all trimesters of pregnancy 1, 2. The evidence demonstrates:

• No increased risk of adverse pregnancy outcomes including spontaneous abortion, prematurity, or fetal malformations 3
• Adverse event rates in pregnant women (4.02/100,000 doses) are actually lower than in non-pregnant women aged 18-64 years (5.9/100,000 doses) 3
• No demonstrated maternal complications or adverse fetal outcomes associated with inactivated influenza vaccination 4

The cell culture-derived quadrivalent vaccine specifically showed excellent safety in pregnant women during the 2019-2020 season, with no reports of spontaneous abortions, prematurity, or fetal malformations 3.

Timing of Administration

Vaccination can be administered during any trimester of pregnancy, ideally at least two weeks before delivery 2. The timing should be based on vaccine availability and should not be postponed unless significant medical contraindications exist 2. Recent evidence shows no significant differences in seroprotection, seroconversion rates, or transplacental antibody transfer between women vaccinated in the second versus third trimester 5.

Dual Protection Benefit

Maternal vaccination provides protection for both mother and infant:

• Maternal protection: Pregnant women face increased risk of severe and complicated influenza, including death 4
• Neonatal protection: Seroprotection rates in neonates range from 59% to 97% for different vaccine strains through transplacental antibody transfer 5
• Infant immunity: Maternal antibodies provide passive protection until infants can receive their own vaccination at 6 months of age 1

Contraindications

The only absolute contraindication is:

• Severe allergic reaction (anaphylaxis) to a previous influenza vaccine dose or any vaccine component

Critical distinction: Live attenuated influenza vaccines (intranasal formulation) are contraindicated in pregnancy 2, 6. However, Influvac Tetra is an inactivated vaccine and is therefore safe and recommended.

Common Pitfalls to Avoid

1. Do not delay vaccination waiting for a specific trimester - any trimester is appropriate 2
2. Do not confuse inactivated with live attenuated vaccines - only live vaccines are contraindicated 2
3. Do not withhold vaccination due to thimerosal concerns - no scientific evidence supports adverse events in children born to women who received thimerosal-containing influenza vaccines during pregnancy 4
4. Do not skip vaccination in previously vaccinated women - baseline seroprotection correlates with previous vaccinations, but annual vaccination is still necessary 5

Expected Tolerability

Over 43% of pregnant women report mild injection site reactions, but severe or unsolicited adverse events are not expected 5. The vaccine is well-tolerated with a favorable benefit-risk profile 3.