Slow uptake of the seasonal flu vaccine could leave thousands of people at increased risk of infection. According to the Royal College of General Practitioners, the number of flu vaccinations delivered so far this year is down 6% on last year. And uptake is low across a range of vulnerable groups including the over-65s, children under five, and those with serious long-term health conditions such as chronic heart, lung or kidney disease.
We don’t know why the uptake has been so low, but we do know the reasons why this has been the case in previous years. They include concerns about the safety of the vaccine and false beliefs that the side-effects of the vaccine are worse than the actual disease. Some may also not believe that they are at risk from the disease or are sceptical about the value of vaccination. Another factor, related to the low effectiveness of the vaccine during last year’s flu season, may have contributed.
How flu vaccines are developed
Each year, a global flu surveillance team – with input from WHO (World Health Organisation) flu labs in Atlanta, London, Melbourne and Tokyo – tries to predict which strains of the virus are most likely to be prevalent in the coming year. Information from the analysis of thousands of influenza viruses identified by the different laboratories is pooled and, on the basis of this, the WHO advises governments on the vaccine composition for the next season.
Three key strains of flu virus are identified by WHO to be incorporated into a “trivalent” vaccine that will tackle the predicted forthcoming strains. These recommendations are made six months in advance of the flu season so that pharmaceuticals companies have enough time to make and distribute the vaccine.
One bad year
During the 2014-15 flu season, the effectiveness of the vaccine in the UK was found to be poor – a mere 3%. This compares unfavourably with previous years where effectiveness rates were usually around 50%. It is possible that the low rates of effectiveness reported could have diminished both the public and health professionals’ confidence in the vaccine.
The effectiveness of the flu vaccine depends on a number of things, including the coverage of vaccination and the efficacy of the vaccine. Although the vaccine can provide moderate protection against the flu, the level of protection can vary widely from season to season. On average, flu vaccine efficacy is estimated to be around 59% in adults and 83% in children. Higher levels of effectiveness are achieved in years when there is a good match between the vaccine and the circulating strains of flu virus.
Science and luck
The predictions about which flu strains are likely to be the most prevalent depend as much on luck as it does science. Sometimes, as in the 2014-15 flu season in the UK, the predictions can go horribly wrong. In this case, the vaccine offered poor protection against flu infection caused by one particular subtype of virus: A(H3N2).
The main reason for this is that the genetic make-up of the flu virus is unstable and new strains and variants are constantly emerging. If the emerging strain is different enough from the ones predicted to be a problem by WHO, this can make the vaccine ineffective. By the time it is apparent that the vaccine is ineffective – usually around mid-flu season – it is too late to develop a new vaccine to tackle the new strain of flu.
Not a trivial illness
One commonly held belief is that flu is not a serious condition. A lot of people mistake the common cold as flu. But the flu is highly contagious, and infection can lead on to severe illnesses including pneumonia. In groups of people at high risk of being infected with the virus (due to poor immune systems), such as the elderly and those with existing health problems, the flu can cause considerable harm and even death – especially in the elderly.
The flu vaccine can protect people from getting the flu, or it can make the disease milder in those who become infected. Those are the direct benefits of the vaccine. But there is also indirect protection.
Between 56% and 73% of the population is protected indirectly by flu vaccines, through what’s known as “herd immunity”. Herd immunity helps to break the disease’s chain of transmission because too few people are susceptible for the disease to be passed on. Lower vaccination uptake lowers this indirect protection.
One estimate was that as many as 1.2m cases of flu may be prevented each year in the UK by flu vaccination. Flu vaccination has been reported to reduce deaths in the over-65s by 4.6% and reduces hospital admissions for pneumonia and flu by around 8.5%.
In recent years there has been a good match between the vaccine and the circulating strains of flu. The 2014-15 flu season was an unfortunate blip. Hopefully, people won’t be put off by this one wrong prediction because the consequences of poor vaccine uptake could be huge.
Andrew Lee also works for Public Health England as a Consultant in Communicable Disease Control.