Wednesday October 24 2007
Flu jab can reduce the length and severity of illness
Flu vaccines are not helping elderly patients and, despite vaccination programmes, the number of hospital admissions due to flu is not being reduced, reported The Times and other newspapers. The study by the Health Protection Agency “will fuel doubts over the effectiveness of the vaccine in older people” the newspaper said, and although the researchers are not recommending an end to the vaccination programme, they suggest other measures should be considered which might reduce hospital admissions such as treating chest infections, improving housing and promoting giving up smoking.
This story is based on a study that investigated the effect of the flu vaccine on the number of hospital admissions over a winter period. The study did not investigate whether vaccination could prevent flu infection. In addition, this study looked only at people who were already ill, and at the current time there is insufficient evidence from this study alone to conclude that influenza vaccinations are unnecessary for a vulnerable group of the population during the winter period.
Where did the story come from?
The research was carried out by Dr Rachel Jordan of the Health Protection Research and Development Unit of the Health Protection Agency (based at the University of Birmingham) and other colleagues from the HPA and at Universities and hospitals in Birmingham, Nottingham Derby, and Aberdeen. The main sponsor of the study was the British Lung Foundation. It was published in the peer-reviewed medical journal Vaccine.
What kind of scientific study was this?
This was a case-control study of sick, elderly people, which aimed to compare those who were admitted to hospital with an acute respiratory illness (cases) with those that presented to the GP with an acute respiratory illness but did not require hospital admission (controls). The participants were part of a larger study that was examining the risk factors for winter hospital admissions due to respiratory illness.
The researchers used a group of elderly people aged between 65 and 89 years old who went to the GP with an acute respiratory illness (or acute worsening of a pre-existing condition) between October 2003 and March 2004. The researchers selected six controls for each hospitalised case and these were matched as closely as possible in terms of sex, age and date of GP consultation. They examined GP records to obtain information about medical diagnoses, pneumococcal vaccinations, and whether the patient had received the recommended influenza vaccination for that winter in the three weeks prior to the start of the study.
All patients included in the study were invited for interview with a nurse to look at social, medical and lifestyle factors. The study excluded patients with dementia and those who were unable to take part in the interview. Of the potential 3,970 people included in the original group, 157 cases and 639 controls were interviewed and included in the study analysis.
What were the results of the study?
The researchers found there to be no difference in the rates of vaccination between those who were hospitalised for their illnesses and those who weren’t; 74.5% of the hospitalised patients had been vaccinated compared with a vaccination rate of 74.2% in patients who weren’t hospitalised. The difference remained non-significant even when adjusting for potential contributing factors such as chronic obstructive pulmonary disease (COPD), other medical illnesses, smoking and age.
What interpretations did the researchers draw from these results?
The researchers conclude that in ill people, influenza vaccine did not reduce the number of hospital admissions due to respiratory illness during a typical winter.
What does the NHS Knowledge Service make of this study?
Although this study can provide some data on the effect of flu vaccination on the numbers of hospital admissions due to a respiratory illness over a winter period, several points must be kept in mind when interpreting the study. Newspaper headlines such as “flu jabs fail to cut illnesses” may lead you to believe that this study was looking at whether the vaccination could prevent infection with the influenza virus, which is not the case.
- The study only enrolled people who had presented to their GPs with “an acute episode of respiratory infection or acute exacerbation of pre-existing disease”, i.e. people who were already sick. As such, it was designed to answer a very specific question about whether the influenza vaccination reduces “respiratory admissions” (which could include flu or not) to hospitals in those who are ill. The study could not and did not intend to determine whether the influenza vaccination can prevent infection.
- Grouping people under a broad definition of presentation – “acute respiratory illness or acute exacerbation of a pre-existing respiratory disease” – means that those with a wide variety of both viral and bacterial infections such as upper respiratory tract infections (coughs, colds, sore throats), influenza, acute bronchitis, infective exacerbations of COPD, and pneumonia would have been included. Through this method, it isn’t possible to separate those patients who were admitted specifically for influenza. As the researchers conclude, their study shows that “influenza is not the sole driver of winter respiratory admissions”.
- There are different types of influenza infection. Influenza is a virus, and different strains circulate during different seasons. Vaccinations are prepared before the flu season starts and are designed to protect against the strains that are predicted to be predominant. It is not always possible to get this 100% correct and the vaccination is always more effective in seasons where it matches well with the strains of virus that are causing infection. The researchers themselves note that “in the 2003–2004 season, the circulating virus showed antigenic drift compared with the vaccine strain”. This means that the vaccine would not offer full protection against flu that season. This study cannot be generalised to predict what happens in seasons where the vaccine is fully matched to the viruses that are causing infection in the population.
- Controls were matched for age, sex and date of consultation but there are many other factors that could impact upon whether hospitalisation could be required for a respiratory illness, such as presence of asthma, COPD, or having a series of repeated infections.
This study suggests that influenza is not the “sole driver” of admissions to hospital for respiratory infections and that relying on a vaccine to prevent flu in order to reduce the winter bed pressures in hospitals is not sufficient.
This study was not set up to determine whether the vaccination works to prevent influenza infection in the elderly. The researchers themselves say that their results do not “negate the need for influenza vaccine, as other studies show small but demonstrable benefits in reducing both infection (an outcome this study did not look at) and subsequent morbidity and mortality in the elderly, particularly in a season where the vaccine is well-matched and there is high viral circulation”. The efficacy of the vaccination in preventing infection is a separate issue and we support the call for further well-designed research to answer this question once and for all. The elderly should continue to be vaccinated against flu while this research is being conducted.
Sir Muir Gray adds...
Hospital admission is determined by many factors, of which the incidence and severity of disease are but two. This does not mean that immunisation should be stopped; if you are offered an immunisation this study should not influence your decision, immunisation does much more good than harm and is still to be recommended.