Thursday September 25 2008
Women were vaccinated after their seventh month of pregnancy
“Pregnant women are set to be offered flu jabs from next year to protect the health of hundreds of thousands of babies”, says The Daily Telegraph. The paper quotes several sources, one of whom is a member of the government advisory panel the Joint Committee on Vaccination and Immunisation, and says it is now "very likely" that pregnant women will be given the jabs from next year. The Telegraph suggests that advisors first called for pregnant women to be vaccinated in 2006, but the plan was turned down due to concerns that it would not be cost effective because of the huge numbers of women who would need the jab.
The story is based on a study carried out in Bangladesh where the flu vaccine was given to women after their seventh month of pregnancy and reduced flu in babies up to six months old by 63%. It prevented approximately one third of all febrile (feverish) respiratory illnesses in mothers and young infants. No doubt the study will be used to inform policy in the UK, but more discussions will be needed and other research results (including any evidence of harms and/or costs) will be taken into account by the advisory group before any universal immunisation programme is rolled out.
Where did the story come from?
Dr K. Zaman and colleagues from the International Centre for Diarrheal Disease Research in Bangladesh, along with others at the Bloomberg School of Public Health and Johns Hopkins University departments in Baltimore, US, carried out this research. The study was supported by various research foundations, including the Bill and Melinda Gates Foundation, the US Agency for International Development (USAID), pharmaceutical companies and the Bloomberg School of Public Health at Johns Hopkins University. It was published in the peer-reviewed medical journal: The New England Journal of Medicine.
What kind of scientific study was this?
This was a randomised controlled trial in which 340 mothers were given an immunisation of either inactivated influenza vaccine (the influenza-vaccine group) or an alternative immunisation with a pneumococcal vaccine (the control group). Influenza, or flu, is a disease caused by a virus, whereas pneumococcal infections, which include pneumonia and meningitis, are caused by bacteria. Results were assessed by weekly interviews of the mother up to 24 weeks after birth.
The researchers provide some background to the trial, saying that young infants and pregnant women are at increased risk for serious consequences of influenza infection. They note that in the US, inactivated influenza vaccine is recommended for pregnant women but is not licensed for infants younger than six months of age. They were interested in seeing if the inactivated influenza vaccine administered to mothers during pregnancy was effective in preventing laboratory-confirmed influenza. They reported respiratory illness with fever in the babies of these mothers when compared with a pneumococcal vaccine. The pneumococcal vaccine they used in the control group was a 23-valent pneumococcal polysaccharide vaccine, which is used to protect against pneumococcal infections such as ear infections, sinus infection, pneumonia, blood infection (bacteraemia) and meningitis (infection of the covering of the brain).
Mothers were screened for suitability to enter the trial, and 340 were randomised to two treatment arms. Women were excluded if they had a past record of general ‘systemic’ disease, a previous complicated pregnancy or early delivery, miscarriage or medical abortion, birth anomaly or reaction to vaccines in the previous three years. When assessed at 24 weeks, the groups contained 316 mothers and 316 infants.
The researchers clinically assessed all infants with a febrile respiratory illness, and ill babies had a blood test to confirm the diagnosis of influenza. They also estimated the incidence of illness, the rates of illness in each group, and the overall vaccine effectiveness.
What were the results of the study?
The study ran from August 2004 to December 2005, and the researchers report that “among infants of mothers who received influenza vaccine, there were fewer cases of laboratory-confirmed influenza than among infants in the control group”. There were six cases of confirmed cases of influenza (confirmed using the blood test) in the first group compared with 16 cases in the control group. This equates to a vaccine effectiveness of 63% (95% confidence interval [CI], 5–85), which means that 63% of cases that would have occurred were prevented by use of the vaccine.
Respiratory illness with fever occurred in 110 infants in the influenza-vaccine group and 153 infants in the control group. This meant that 29% (95% CI 7–46) of cases of respiratory illness were prevented. Mothers also benefited from the immunisation, with a reduction in the rate of respiratory illness with fever of 36% (95% CI 4–57).
What interpretations did the researchers draw from these results?
The researchers say that inactivated influenza vaccine reduced proven influenza illness by 63% in infants up to six months of age, and averted approximately a third of all febrile respiratory illnesses in mothers and young infants. They conclude that “maternal influenza immunisation is a strategy with substantial benefits for both mothers and infants.”
What does the NHS Knowledge Service make of this study?
The authors make several comments about their trial. They note that:
- The confidence limits for the effectiveness of passive immunisation were wide. This may have been because the numbers in this study were small, and implies that if this study were repeated it is possible that other estimates of the vaccine effectiveness would result. However, the authors also mention that the estimate of effectiveness against laboratory-proven influenza is similar to those reported in trials of active influenza vaccine in infants older than six months of age, and these differ from the results of studies that have reviewed patient records only.
- They were unable to assess the more rare outcomes of influenza, such as hospitalisation and severe illness, because the study did not have statistical power (sufficient numbers of recruits).
- They did not carry out virologic studies, and they were unable to tell what the strains of influenza virus were and if these were those targeted by the vaccine. Data describing the variety of influenza viruses in Dhaka during the study period had been reported previously.
Overall, this is a reliable study which, although conducted in Bangladesh, does demonstrate the overall effectiveness of the vaccine. No doubt it will be used to inform policy in the UK, but more discussions will be needed, and other research results (including any evidence of harms and/or costs) taken into account by the advisory group before any universal immunisation programme is rolled out.
Sir Muir Gray adds...
Illness in pregnancy is bad for both parties and should be prevented if possible.