Influvac® and Invivac® both stimulate the B lymphocytes of the body’s immune system to produce antibodies, without causing the disease. When the body is exposed to the sub-units (antigens) in Influvac® or Invivac®, the immune system produces antibodies in the same way as occurs in an influenza infection. These antibodies are specific to the influenza virus particles present in the vaccine and their function is to help the body recognize and kill these foreign organisms. This protective immunity occurs within two to three weeks after vaccination, and the duration of the immunity varies, but usually lasts 6 to 12 months. It enables the body to launch a swift attack against the influenza virus, before it can cause disease.
Children who have not previously been vaccinated against influenza should receive a second dose at least four weeks after their first vaccination.

Invivac® also has the potential to activate cytotoxic T-cells. This broader immune response is important for the protection against influenza-related diseases. Cytotoxic T-cells recognize and eliminate infected cells and are therefore important for the recovery process after an influenza infection. Elderly people may have a weakened immune system; therefore T-cell stimulation by the virosomal vaccine Invivac® may be especially beneficial for the elderly.

Efficacy
The efficacy of the influenza vaccines, conventionally measured as the levels of hemagglutinin antibodies in the serum, depends greatly on age. In children and adults up to 60 years of age, the protection offered by whole virus, split, or subunit vaccines is 70 to 90% according to numerous studies during the past five decades. If a person has been vaccinated but nevertheless contracts influenza, the illness will be less severe as was shown in the elderly, namely about 30 – 40%. Protection against influenza illness in the elderly results in 80% protection from death related to influenza illness.

For the general population Influvac® and Influvac® give approximately 70 to 90% protection against getting influenza. As is shown in the table the efficacy of Influvac® is somewhat less in the elderly. This is most likely due to the ageing of the immune system.

In the next table the protection rates of Invivac® with that of Influvac® in persons older than 60 years of age are compared.

Both vaccines meet the efficacy criteria demanded by European Agency for the Evaluation of Medicinal Products (EMEA). Invivac® is at the least as effective as Influvac® in generating protection and is likely to have an added value, particularly in elderly patients.

The influenza virus is constantly changing its structure (mutating). This means that each year a different vaccine containing different strains of the virus is required. Each year Influvac® and Invivac® contain the strains of influenza that have been identified and recommended by the World Health Organization and the EU as likely to be prevalent during the coming influenza season.

Safety
Influvac® and Invivac® belong to the newest vaccines, called sub-unit influenza vaccines. Subunit vaccines cause the least side effects of all available influenza vaccines. The first available influenza vaccines contained killed whole viruses. This vaccine was effective, but caused more side effects. Over the years, companies such as Solvay Pharmaceuticals have been able to separate those parts of the virus that do not contribute to the immune response from those that are effective. This preparation method and the advanced purification techniques make Influvac® the best tolerated influenza vaccine.

Influvac®
Local vaccine-reactions after vaccination occur at the site of vaccination (usually m. deltoideus or the upper arm). They are in part caused by the simple trauma of the needle used for injection, and in part by the vaccine constituents. In the next table the frequency of local and systemic symptoms per age group occurring after vaccination with Influvac® are presented. Only one symptom (pain on injection site) is frequent (32 – 36%) in persons of 18 – 60 years of age.

Systemic symptoms are caused by the body’s own production of interferon activated in some of the persons vaccinated as part of the immune reaction.
The systemic symptom which is most frequently reported is headache.

Both local and systemic reactions are usually mild and transient (one to two days). When persons vaccinated are asked about the overall degree of inconvenience they suffer from Influvac®, fewer than 1% report severe inconvenience.

Other adverse events occur extremely rarely and have to be assessed by Post Marketing Surveillance, which is based on more than 100 million doses Influvac® sold since 1982. Examples: Allergic reactions in 1.4 cases per million doses and Guillain-Barré Syndrome in 0.9 case per million per month. The use of Influvac® is not associated with an elevated incidence of GBS.

Invivac®
In 2,865 subjects Invivac® shows a safety pattern similar to that of Influvac®. Therefore we can conclude that Invivac® is as safe as Influvac®.
The tolerability of Invivac® was judged to good or very good by 98% of the persons vaccinated and 99% agrees to be vaccinated again.