A controlled study published in The Lancet on May 31st, 2016, has concluded that a new maternal immunization form, that utilizes influenza vaccines is safe, effective and can protect infants from catching the infection for up to four months.

Despite being at a heightened risk of influenza infection, infants are not given influenza vaccination until they are six months of age. Maternal immunization, therefore, is an alternative strategy of providing protection to newborns from viral infections until they are old enough to be immunized i.e., six months of age. During the gestation period, the mother’s antibody protects the fetus from viral infections.

The aim of the study was to investigate the potential efficacy and the immunogenicity of the inactivated influenza vaccine against the laboratory-confirmed influenza virus among infants of immunized mothers. Results showed that preterm vaccination of mothers with trivalent inactivated influenza vaccine or quadrivalent meningococcal vaccine was remarkably effective in providing protection to infants till four months of their age. The efficacy, however, decreased as the haemagluttination inhibition antibody titers diminished and completely disappeared at the follow-up at six months.

Study

The study was conducted in Bamako, Mali, a poor and underdeveloped country with the world’s seventh highest infant mortality rate. The study was conducted from Sept 12th, 2011-Jan 28th, 2014. A total of 4,193 pregnant ladies were included in the study, out of which 2,108 women were injected with the trivalent inactivated influenza vaccine and 2,085 were given the quadrivalent meningococcal vaccine. 3,661 women were followed up until six months after the delivery and 4,105 live births happened. 1,797 out of 2,064 infants in a group were given trivalent inactivated influenza vaccine while in another group, 1,793 out of 2,041 infants were given quadrivalent meningococcal vaccine. All infants were followed up until six months of their age.

Once vaccinated, the mothers were preliminarily observed for 30 minutes. After seven days of vaccination, they were interviewed for any kind of local and systematic reaction. A complete clinical evaluation was done after 28 days.

Composition Of The Vaccines

The composition of the trivalent inactivated influenza vaccine varied throughout the trials whereas the quadrivalent meningococcal conjugate vaccine was composed of 4µg each of neisseria meningitides serogroup A, C, Y and W-135 polysaccharides conjugated to diphtheria toxoid protein. A single dose of 0.5ml trivalent inactivated influenza virus or quadrivalent meningococcal conjugate vaccine was injected in the deltoid muscles of the participants.

Objectives And Outcomes

There were two main objectives of the study.

  1. To check the efficacy of the vaccine administered to women at any time of the preterm period.
  2. To check the efficacy of the vaccine given to women at least 14 days from their preterm period.

The outcomes were completely unexpected. The first case of laboratory-confirmed influenza virus was observed by 6 months. The secondary outcomes were due to the occurrence of some influenza-related illness in infants as well as the occurrence of the first case of febrile infection-like illness in women. Additionally, women also experienced some physiological reactions after getting infected.

Tertiary outcomes included the occurrence of multiple strains of the virus found in the study.  Additionally, maternally derived haemagluttination inhibition antibodies were analyzed among infants at different ages — at birth, age three and age six months. The detection of the types and sub-types of viruses was done through reverse transcription polymerase chain reaction (RT-PCR) and heamagluttination inhibition antibody measurements. 

Statistical Data

Vaccine efficacy was observed in both intention-to-treat and pre-protocol population analyses. For the intention-to-treat analysis, the laboratory-confirmed attack rate among infants aged six months and born to recipients of quadrivalent meningococcal vaccine was 2.2%. A rate of 0.9% was observed among infants born to recipients of trivalent inactivated influenza vaccine. Similarly, for the pre-protocol analysis, the vaccine efficacy was assumed to be 60% in infants born to recipients of trivalent inactivated influenza vaccine.

Limitations Of The Study

Women having severe reactions to previous immunizations with influenza vaccines and meningococcal vaccines were excluded. Any women exhibiting an allergy to eggs, eggs proteins, latex and diphtheria toxoid or reaction to any other vaccine component were excluded.

According to the study investigator’s opinion, such allergies could perform as hindrances to the current study and put the participants’ life in danger. This included HIV, hepatitis B virus or hepatitis C, complications with the ongoing pregnancy, cases of congenital anomaly, administration of any immunosuppressant within 90 days before the administration of study vaccine, or any fatal infection.

Physiological Reactions To The New Maternal Immunization Form

Some physical reactions were experienced after the vaccination administration — pain was observed at the injection sites (deltoid muscles) among the women given quadrivalent meningococcal vaccine, more than the women given trivalent inactivated influenza vaccine.

Additionally, approximately 3% of women from both groups experienced some obstetrical and non-obstetrical adverse effects. The children in the trivalent inactivated influenza vaccine group were speculated to have more neo-natal infections than the children in the other vaccine group.

Results And Interpretations

Maternal vaccination with trivalent inactivated influenza vaccine was technically and logistically effective in preventing influenza infection in infants for up to four months.

Recommendations By The World Health Organization (WHO)

Since pregnant women and infants are highly vulnerable to influenza infection, the WHO recommends that pregnant women be the prime recipients of influenza vaccination, particularly because it has been proven that maternal immunization can protect infants from influenza infections.

In order to make the maternal influenza immunization project successful, it is suggested that vaccination prices should be reasonably justified in order to gain benefits and facilitate funding.