The Medical Letter on Drugs and Therapeutics
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1531
Influenza Vaccine for 2017-2018
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 Select a term to see related articles  Afluria   Agriflu   Fluad   Flublok   FluceIvax   flulaval   FluMist   Fluviral   Fluvirin   Fluzone   Fluzone High-Dose   Fluzone Intradermal   influenza   Influenza vaccine   Influvac 

Routine annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a specific contraindication.1

EFFECTIVENESS — The effectiveness of seasonal influenza vaccine in preventing laboratory-confirmed influenza illness depends on the match between the vaccine and circulating strains. Vaccine effectiveness is highest (40-60%) when the match is close, but even when the match is poor, vaccination has been shown to reduce the risk of hospitalization and death from influenza.2-4 For the 2016-2017 influenza season, the adjusted overall effectiveness of the seasonal influenza vaccine against influenza A and B viruses was 42%.5

COMPOSITION — All seasonal influenza vaccines available in the US contain the same two influenza A virus antigens. Trivalent vaccines contain only one influenza B virus antigen. Quadrivalent vaccines contain influenza B virus antigens from the two genetic lineages that have been circulating globally since the 1980s, increasing the likelihood that the vaccine will provide protection against currently circulating strains.6,7

LIVE-ATTENUATED VACCINE — In recent seasons, the live-attenuated influenza vaccine (FluMist) has been significantly less effective than inactivated vaccines in preventing influenza illness in children.8,9 Due to concerns about lower-than-expected effectiveness, the ACIP advises against using the live-attenuated influenza vaccine for persons of any age during the 2017-2018 season.1

OLDER ADULTS — Older adults may have a lower antibody response to influenza vaccination than younger adults and their antibody levels may decline more rapidly.10,11

Recombinant vs Inactivated – Flublok, a recombinant vaccine produced without the use of influenza virus or chicken eggs, contains three times the amount of antigen included in standard-dose vaccines. It has been shown to produce greater antibody responses to influenza A antigens in older adults.12,13 A randomized, double-blind trial in 8604 adults ≥50 years old found that the probability of influenza illness was 30% lower with the recombinant quadrivalent influenza vaccine (Flublok Quadrivalent) than with a standard-dose nonadjuvanted quadrivalent inactivated vaccine.14

High-Dose vs Standard-Dose – In a randomized trial in 31,989 adults ≥65 years old, the high-dose vaccine (Fluzone High-Dose), which contains four times the amount of antigen included in standard-dose vaccines, induced significantly higher antibody responses and was more effective than a standard-dose trivalent inactivated vaccine in preventing influenza illness in older adults (1.4% incidence with the high-dose vs 1.9% with the standard-dose vaccine).15 Recent studies in adults ≥65 years old found that the high-dose influenza vaccine was more effective in reducing the risk of respiratory-related and all-cause hospital admissions and death than standard-dose vaccines.16,17

Adjuvanted vs Nonadjuvanted – The adjuvanted trivalent influenza vaccine (Fluad) contains MF59, an oil-in-water emulsion of squalene oil that increases the immune response by recruiting antigen-presenting cells to the injection site and promoting uptake of influenza virus antigens.18 A randomized trial in 7082 adults ≥65 years old found that, compared to a nonadjuvanted trivalent vaccine, Fluad elicited significantly higher antibody responses against all three strains 3 weeks after vaccination, but the differences did not meet the prespecified criteria for superiority.19 In observational studies, older adults who received the adjuvanted trivalent influenza vaccine were less likely to develop symptomatic influenza illness or be hospitalized for influenza or pneumonia than those who received a nonadjuvanted standard-dose trivalent vaccine.20,21

Adjuvanted vs High-Dose – Both Fluad and Fluzone High-Dose are approved for use in persons ≥65 years old. No studies are available directly comparing Fluad with Fluzone High-Dose. Both have elicited greater antibody responses in older adults than nonadjuvanted standard-dose vaccines, but only the high-dose vaccine has been shown to be more effective in preventing laboratory-confirmed influenza in a randomized trial.15

CARDIOVASCULAR BENEFITS — Meta-analyses of randomized trials found that influenza vaccination was associated with a reduced risk of major adverse cardiovascular events and death in patients at high risk for cardiovascular disease; the reduction in risk was greatest in those with a recent history of acute coronary syndrome.22,23

PREGNANCY — Vaccination of pregnant women not only protects them against influenza-associated illness, which can be especially severe during pregnancy, but also protects their infants for up to the first 6 months of life.24,25

A recent case-control study of 485 cases of spontaneous abortion (gestational age 5 to <20 weeks) that occurred during 2010-2011 and 2011-2012 influenza seasons found that spontaneous abortion was associated with vaccination with inactivated influenza vaccine in the prior 28 days. The composition of the inactivated influenza vaccine was the same for both seasons and included a pandemic H1N1 (pH1N1) strain. Pregnant women who were vaccinated in 2010-2011 could have been vaccinated the previous season with the monovalent pH1N1 vaccine, the seasonal trivalent vaccine which did not contain a pH1N1 strain, both, or neither of these vaccines. A post-hoc analysis found that the association between vaccination and spontaneous abortion was significant only among women who had been vaccinated with a pH1N1-containing inactivated influenza vaccine in the previous season.26 A causal relationship between influenza vaccination and spontaneous abortion has not been established.

The CDC and The American College of Obstetricians and Gynecologists continue to recommend that pregnant women be vaccinated against influenza regardless of trimester of pregnancy.27,28

ADVERSE EFFECTS — Influenza vaccination has been associated with Guillain-Barré syndrome, but the absolute risk is very low, and influenza infection itself has also been associated with the syndrome.29,30

Except for soreness at the injection site, adverse reactions to inactivated influenza vaccines are uncommon. In clinical trials, Fluzone Intradermal Quadrivalent and Fluzone High-Dose have caused more injection-site reactions than standard-dose influenza vaccines. Delivery of Afluria by needle-free jet injector has caused more mild to moderate local reactions than delivery by needle and syringe. Pain and tenderness at the injection site occurred more frequently with Fluad than with the unadjuvanted vaccine.

ALLERGY – A history of a severe allergic reaction to any component of the influenza vaccine is a contraindication to vaccination. The ACIP states that any age-appropriate influenza vaccine can be used for persons who report a history of hives related to egg exposure because a data review including 4172 patients with egg allergy (513 reported a history of a severe allergic reaction) found no occurrences of anaphylaxis after administration of trivalent inactivated influenza vaccine; some mild reactions did occur.31 Persons with a severe egg allergy can also receive any age-appropriate influenza vaccine, but should be vaccinated in a healthcare setting.

CONCLUSION – Vaccination with seasonal influenza vaccine is recommended for all persons ≥6 months old without a specific contraindication, including pregnant women. Quadrivalent vaccines offer broader coverage against influenza B viruses. High-dose, adjuvanted, and recombinant vaccines have been shown to elicit greater antibody responses than nonadjuvanted and inactivated standard-dose vaccines in adults ≥65 years old. Because of concerns about its effectiveness, the ACIP advises against use of the live-attenuated influenza vaccine this season.

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