Side Effects 133

Side Effects

Guillain-Barré Syndrome is seen as the most dangerous side effect of influenza vaccines, aside from manifestations of egg allergy. It is, however, rare: the annual reporting rate decreased from a high of 0.17 per 100,000 vaccinees in 1993-1994 to 0.04 in 2002-2003 (Haber 2005).

The most frequent side effects are pain, redness, and swelling at the injection site (10-64 %) lasting 1-2 days, and systemic side effects such as headache, fever, malaise, and myalgia in about 5 % of vaccinees (Belshe 2005, Musana 2004, Potter 2004). These side effects are largely due to a local immune response, with interferon production leading to systemic effects. Local side effects are more common with whole virus vaccines than subunit or split vaccines, and also more common with intradermal vaccination than intramuscular vaccination.

Since the inactivated vaccines do not contain live virus, they cannot cause influenza infection – often respiratory illness is incorrectly attributed to influenza vaccination. Live attenuated virus vaccines do contain live virus; however, side effects are rare, with a runny nose, congestion, sore throat, and headache being the most commonly reported symptoms, with occasional abdominal pain, vomiting, and myalgia (Musana 2004). They are not recommended for use in children below the age of 5 years, although a study by Piedra et al. (Piedra 2005) showed safety in children above the age of 18 months. Controversies have arisen around the possibility of exacerbated asthma in children between 18-34 months of age (Bergen 2004, Black 2004, Glezen 2004). It should be noted, however, that these vaccines should be avoided in immunocompromized patients.

Recommendation for Use

Indications

Groups to target

The primary groups to be targeted for vaccination can be memorized with an easy mnemonic – FLU-A (Musana 2004).

F – facilities such as nursing homes or chronic care facilities.

L – likelihood of transmission to high risk persons – healthcare workers and care providers can transmit influenza to patients, as can other employees in institutions serving the high risk population groups, as well as people living with individuals at high risk.

U – underlying medical conditions such as diabetes mellitus, chronic heart or lung disease, pregnancy, cancer, immunodeficiency, renal disease, organ transplant recipients, and others.

A – age > 65 years, or between 6-23 months of age

Since the risk of influenza rises linearly from the age of 50 years, some promote the vaccination of those aged between 50 and 64 in addition to those above 65 years of age. In a study of health professional attitudes to such a policy in England, both sides were equally divided (Joseph 2005). Vaccination for those above 50 years of

134 Vaccines

age is recommended in the USA, while all those above 6 months are offered vaccination in Canada.

In the era of a potentially pending pandemic, other groups also have importance for targeting – poultry workers in the Far East are being vaccinated to prevent infection with circulating human influenza strains. This vaccine will not protect against avian influenza strains, but will help prevent dual infection, if infection with avian influenza does occur, thereby reducing opportunities for reassortment of two strains in one human host. For the same reason, travelers to areas where avian influenza is present are advised to be vaccinated against human influenza (Beigel 2005).

Guidelines

The World Health Organisation makes the following recommendations on who should receive influenza vaccines (WHO 2005b-c, WHO 2005f):

!Residents of institutions for elderly people and the disabled.

!Elderly, non-institutionalized individuals with chronic heart or lung diseases, metabolic or renal disease, or immunodeficiencies.

!All individuals > 6 months of age with any of the conditions listed above.

!Elderly individuals above a nationally defined age limit, irrespective of other risk factors.

Other groups defined on the basis of national data and capacities, such as contacts of high-risk people, pregnant women, healthcare workers and others with key functions in society, as well as children aged 6–23 months.

The CDC guidelines are similar, with a few additions (Harper 2004, CDC 2005) -

!Residents of nursing homes and long-term care facilities

!Persons aged 2-64 years with underlying chronic medical conditions

!All children aged 6-23 months

!Adults aged > 65 years – high risk

!Adults aged > 50 years – recommended

!All women who will be pregnant during the influenza season

!Children aged 6 months – 18 years on chronic aspirin therapy

!Healthcare workers involved in direct patient care

!Out-of-home caregivers and household contacts of children aged 0-23 months

South Africa has the following guidelines (summarised from Schoub 2005), dividing the population into 4 groups who may receive the vaccine –

! Category 1 – At risk persons (i.e. at risk for complications of influenza) o All persons over the age of 65 years

o Persons with chronic pulmonary or chronic cardiac disease o Immunosuppressed persons

oPregnancy – women who will be in the second or third trimester during the winter season. Vaccination is contraindicated in the first trimester.