Need to know - Influenza
GP and flu expert Dr Douglas Fleming answers GP Dr Pam Brown’s questions on vaccination, antivirals, spotting symptoms and post-exposure prophylaxis
GP and flu expert Dr Douglas Fleming answers GP Dr Pam Brown's questions on vaccination, antivirals, spotting symptoms and post-exposure prophylaxis
1. How effective is influenza vaccine in preventing influenza infection?
• Provided there is a good match between circulating and vaccine strain – and there usually is – vaccination is always very effective in preventing laboratory-confirmed influenza, regardless of age.
• Vaccination consistently reduces the risk of serious illness likely to lead to admission and death from flu.
• Vaccination in the frail elderly is less effective than in the healthy elderly because immune response deteriorates with age. But it is particularly desirable that this group get the benefit of vaccination even if that is reduced compared with their healthy peers.
• Vaccination can only give protection against flu. There are other respiratory virus infections occurring in winter for which no protection can be expected. Most of these are less serious than flu, except in the frail elderly.
• It takes about 14 days for protective immunity to develop and it is possible to get flu in this period.
The US Centers for Disease Control and Prevention is an excellent source of information on vaccine efficacy. Also Vaccine has just published a very useful supplement with 10 articles on topical issues relating to flu vaccination.
Vaccination policy is based chiefly on the overall cost-effectiveness of vaccination in target groups and that varies between countries depending on national patterns of healthcare delivery.
2. How important is it to give a second dose to children and how does it affect efficacy if the second dose is delayed by pyrexial illness?
It is essential to give a second dose in young children, because the response to a single dose is insufficient. Adults have been exposed to many flu infections and so only need their immunity to be boosted with the most recent virus strains. A two-week delay in receiving the second dose – for whatever reason – will not materially reduce the efficacy, though any delay leaves the child at risk of getting flu in that intervening period.
3. Are there differences between currently available flu vaccines?
There are two main types of flu vaccine: inactivated and live virus. In the UK, we use only inactivated vaccines – manufactured from flu viruses that have been completely destroyed (split virion vaccines) or killed whole virus vaccines.
In recent years several vaccine manufacturers have added materials to the vaccine – adjuvants – to improve the immune response to vaccination, though in some cases these have been associated with increased local reaction at the injection site. From a clinical perspective there is little to choose between these alternatives, though an enhanced immunological response would be beneficial.
Although the attenuated live virus vaccines are not yet available in the UK, there is a suggestion that they confer additional benefit over inactivated vaccines in young children.
4. How do the groups who require antiviral therapy differ from those who qualify for flu immunisation in the UK?
Broadly speaking, the groups targeted for vaccination are also the groups recommended to receive antivirals when flu viruses are known to be circulating in the community.
5. Do the same groups qualify for post-exposure prophylaxis?
Post-exposure prophylaxis is recommended for unvaccinated people in recognised risk groups but that has not been extended to carers. More detailed recommendations are made for those in residential institutions.
Specific guidance and the evidence base for is available here.
6. What is the rationale for restricting immunisation to pregnant women due to deliver between November and March, and is this recommended currently?
The vaccination of pregnant women in the third trimester is recommended policy in the USA but not in the UK except for pregnant women in recognised risk groups. The Department of Health is keeping the issue of flu vaccination and pregnant women under review.
Vaccines are usually given in October and November to provide protection over the rest of the winter. The risks of flu are mostly confined to the late stages of pregnancy and the confinement period. The recommendation – where applicable – is concerned with protecting women who deliver during the winter1.
7. How should we differentiate flu from other viral URTIs to allow us to prescribe antiviral treatment appropriately?
Unfortunately there is no simple answer. The range of symptoms caused by flu is similar to that caused by other respiratory viruses. In adults, illness caused by flu is generally more severe than that caused by most other winter viruses and, in particular, the onset is more acute with early manifestation of constitutional symptoms such as fever and headache in addition to the widely recognised respiratory symptoms.
In children, the distinction is even more difficult, though the acuteness of onset and the often rapid spread among family and local contacts provide additional clues. NICE recommends the use of surveillance data to prompt the use of antivirals.
8. How does flu present in infants and pre-school children?
The younger the child, the more dramatic and acute the onset. Sometimes there is little more than a high fever and refusal to feed. Earache is a common presenting feature and – although not common – febrile convulsions are sometimes seen.
In schoolchildren, absence of several classmates at the same time is a clue, but for some it is difficult to distinguish flu from the common cold especially if the infection is influenza B.
9. What non-drug infection control measures should we be advocating to patients when flu is circulating?
Flu spreads chiefly by respiratory droplets. The more that people are coughing and sneezing and the closer they are to each other, the more likely they are to spread flu. The first point is not to mix if you have a suspicious illness – and in particular a raised temperature.
Second, minimise droplet spread by using paper tissues when coughing or sneezing and disposing of them promptly and hygienically.
Finally, commonsense hygiene such as regular hand-washing and reduced close contact – not kissing children, for instance – reduces the risk of spread by contagion.
There has been a lot of discussion recently about the benefit of wearing masks and these must be adequate to restrict the passage of flu viruses. A flu sufferer may limit the dispersal of virus-laden aerosol droplets by wearing such a mask, but a healthy person carrying on routine daily tasks is not likely to reduce inhalation of virus exhaled in the earliest stages of flu illness. A review in the BMJ earlier this year considered this issue2.
10. What are the key differences between the antiviral therapies, and does it matter which we prescribe in an epidemic ?
There are two main classes – the adamantanes and the neuraminidase inhibitors (NIs).
The adamantanes are not effective against influenza B infections. They have been associated with the development of resistance against several flu virus strain types and have neurological side-effects, which are a problem in the elderly. They are no longer recommended for general use.
There are two NI antivirals, oseltamivir, administered by tablet, and zanamivir administered by oral inhalation. They act by blocking the replication of both influenza A and B viruses.
Apart from the relative acceptability of the routes of administration, until now there has been little to choose between them in terms of clinical efficacy. In the past 12 months we have seen substantial numbers of people with flu caused by an AH1N1 virus resistant to oseltamivir but sensitive to zanamivir.
In future we will need to be more particular about the virus type when flu is circulating to ensure appropriate prescribing. To date this problem has arisen solely with AH1N1 viruses.
It is important to appreciate the importance of early administration of antivirals. In recent epidemics there has been no detectable benefit from treatment 48 hours after onset of symptoms. The maximum benefits are achieved if treatment is started within six to 12 hours3.
11. NICE does not recommend use of amantadine – is there now any role for it?
There is no immediate role for amantadine in the management of seasonal flu epidemics, but it may have a place in a pandemic – either for treatment in combination with an NI or perhaps in prophylaxis in some specific target groups.
12. What are the key signs and symptoms of bacterial superinfection or other respiratory complications in patients with flu?
Timing is critical. Flu symptoms usually peak on the second or third day. If a patient is deteriorating after that, especially if they are increasingly breathless, secondary infection should be considered. There are groups of people such as those with chronic pulmonary and cardiac diseases who are particularly prone to bacterial complications.
13. What non-respiratory complications can occur?
Otitis media commonly occurs in children, though this should be considered as a respiratory complication. The high fever of flu may lead to dehydration and cause febrile convulsions.
In the elderly, flu often causes confusion and there are increased hospital admissions and deaths because of cardiovascular disease during flu epidemics.
14. In which returning travellers with fever and URTI symptoms should we consider avian flu and how should we investigate and manage the patient?
We are currently in Pandemic Alert Period Phase 3, summarised as: No, or very limited, human-to-human transmission of a new flu virus.
In this phase it is important for both clinicians and virologists to recognise the unusual. Downloadable guidance on the management of respiratory infections in travellers from abroad – whether returning home or new arrivals – is available from the HPA.
People with high fever of uncertain origin who have recently arrived in this country need to be investigated promptly and adequately. The local infectious disease specialist at the Health Protection Agency is always available to offer help and advice.
Dr Douglas Fleming is director of the RCGP Birmingham Research Unit, concerned with the surveillance of diseases as they present to GPs
Competing interests: Dr Fleming has served on advisory committees to pharmaceutical and vaccine manufacturers. He has been reimbursed by them to attend international meetings and to present lectures on flu-related matters.
What I will do now What I will do now
Dr Pam Brown reflects on the answers to her questions
• I'll bear in mind that the flu vaccine takes about 14 days to produce immunity
• I'll continue to try to ensure children attend for their second flu immunisation, and reassure parents that short delays caused by another illness will not affect efficacy
• I'll ask more detailed questions about the speed of onset and duration of symptoms in patients who may have flu, and be aware that uncomplicated flu symptoms should peak by days two to three, so later deterioration suggests
a secondary bacterial infection
• I'll continue to advise those with
flu-like illnesses to stay at home and encourage the frail elderly and other at-risk groups to avoid crowded places when flu is circulating
• When it becomes appropriate to prescribe antivirals, I'll only do so if the patient can start using them within
48 hours of onset of symptoms
• I'll keep a note of the references provided so that we have them on hand this winter
Dr Pam Brown is a GP in Swansea