Seasonal influenza vaccine is usually given in multivalent form consisting of the circulating strains. Presently trivalent influenza vaccine is given which contains components of influenza A H1N1, H3N2 and influenza B.

Aim of influenza vaccination: To protect against infection and disease and to increase the herd immunity to prevent the spread of infection.

Recommendation: The recommendation for influenza vaccination in majority of the countries worldwide is for the elderly and high-risk individuals.

In the USA, national influenza vaccination in 2010 included 6 months to 18 years old.

Timing of vaccination: Annual vaccination scheme is recommended for influenza vaccination. This is based on the rationality that the antigenic variation in the circulating strains becomes sufficient enough to decrease the efficacy of the vaccine in the subsequent year. Therefore, every year the vaccine strains are selected based on the circulating strains worldwide.

• Vaccine is recommended prior to the start of the influenza season.

• In western countries where influenza season occurs in the winter, it is given prior to winter season.

Types of vaccine: Available in inactivated and live attenuated forms.

Preparation of seed virus: Seed virus contains the HA and NA surface antigens from the vaccine virus which are selected from the circulating influenza virus strain for that particular year for vaccine preparation and remaining six genes from the donor virus.

Seed virus is prepared either by co infecting these two types of virus strain in egg or by the process of reverse genetics.

Inactivated vaccine: Inactivated vaccines are available in three types of formulations; whole virus vaccine, split virus and subunit vaccine.

• Whole virus vaccines are prepared from the harvested allantoic fluid which has been infected with the seed virus. The harvested fluid is chemically inactivated using formalin or beta-propiolactone, then concentrated and purified.

 • Split virus vaccine is prepared in the similar manner with an additional step of detergent treatment which removes the virus envelop exposing the virus nucleic acids.

• Subunit vaccine has an additional step of purification.

Dose: One dose of inactivated vaccine contains 15 µg of HA per strain.

• For individuals >9 years: One dose is given.

 • For 6 months to 8 years: Two doses at 4 weeks interval.

Immunogenicity: Antibody production against HA antigen is the main mechanism of protection. Wild virus vaccine is more immunogenic than split or subunit vaccine particularly in children.

Adverse reaction:

• Local reactions: Pain, induration redness at the local injection site.

 • Systemic reactions such as fever, malaise and headache.

• This is mainly due to the presence of residual egg protein.

• More commonly seen with wild virus vaccine than split or subunit vaccine.

Live attenuated vaccine (LAIV): This is prepared using temperature sensitive, cold adapted strain attenuated by serial passage.

It induces mucosal IgA , serum IgG as well as cellular immunity and considered to be more immunogenic than inactivated vaccine.

LAIV is recommended in above 2 years age group.

Contraindication:

• Pregnant and immunocompromised individuals.

 • Individuals with asthma.

Table 1 describes the differences between inactivated and live attenuated influenza vaccines.

Table1. Differences between inactivated and live attenuated influenza vaccine

Inf A (H1N1) 09pdm virus vaccine: Both inactivated and live attenuated vaccines are available against Inf A (H1N1) 09pdm.

During the pandemic, monovalent vaccine of Inf A (H1N1) 09pdm virus was given. Presently, the virus has become a component of seasonal vaccine. The differences between inactivated and live attenuated vaccines are principally same as that for seasonal vaccine.

H5N1 vaccine: Several vaccine candidates including high pathogenic HA, low pathogenic HA, DNA vaccines and virus-like particles (VLP) are under clinical trials.

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مواضيع ذات صلة

Vaccination (Active Immunoprophylaxis)

Dengue Vaccine

Applications of Vaccines

Viral Vaccines

Microbiota, Chronic Infections, and Vaccines

Vaccines and the Role of Pre-existing Immunity

Examples of Protein Subunit Vaccines

Methods for Using Full-Length Antigens (Proteins) as Vaccines

Pan-Genomic Analysis

Reverse Vaccinology

Improving Vaccines over Natural Immune Responses

Selecting Vaccine Antigens