Equal but Not the Same—2021 Update on Influenza Vaccines

One key distinction amongst vaccine merchandise is decided by the variety of viral strains included within the preparation. For instance, trivalent vaccines include 3 strains, together with 2 influenza A and 1 influenza B. Quadrivalent vaccines include 4 strains, together with double protection for each A and B strains.2 Annually, the CDC and the World Well being Group publish suggestions on the composition of strains to be included within the vaccine based mostly on anticipated widespread presence. The really helpful composition of strains for each trivalent and quadrivalent vaccines for the upcoming 2021-2022 season is listed in Desk 1.4

Adjuvanted Vaccines

Each trivalent and quadrivalent flu vaccines can be found with an adjuvant, which is an ingredient included to create a extra sturdy immune response.2 MF59 is an adjuvant that has been included within the vaccines since 2016,5 and it enhances antigen uptake, growing migration and activation of immune cells.6 The adjuvanted formulations are permitted for people 65 years and older.2

Egg-Containing Vs “Egg-Free” Vaccines

Most of the influenza vaccines at present accessible are produced utilizing egg-based manufacturing. Nevertheless, newer strategies of manufacturing have been developed and supply benefits over the standard methodology. Presently, there are 3 strategies used to supply the totally different formulations of the influenza vaccine: egg-based manufacturing, cell-based manufacturing, and recombinant expertise.7

Most influenza vaccines are produced utilizing egg-based manufacturing. This methodology can be utilized to supply dwell or inactivated influenza vaccines. The egg-based course of begins with candidate vaccine viruses (CVVs), that are grown in rooster eggs and offered by the CDC or a accomplice group. The CVVs are inserted into fertilized rooster eggs and allowed to duplicate for a number of days. After this time, the viral materials is collected, killed (if getting used for an inactivated vaccine), and purified to supply the viral antigens for the vaccine. Though egg-based manufacturing is essentially the most extensively used methodology, these vaccines typically can’t be utilized in folks with egg allergic reactions and might take longer to supply in contrast with different strategies.2 Vaccines grown in eggs are additionally susceptible to present process egg-adapted modifications, which might result in a much less efficient vaccine being produced.7,8

As of 2012, the FDA permitted the cell-based manufacturing course of for use to supply inactivated influenza vaccines. This course of is pretty just like the egg-based methodology; nevertheless, the CVVs are grown in cells (as a substitute of eggs) after which inserted into cultured mammalian cells to duplicate. The viral materials is then extracted, killed, and purified to be used within the influenza vaccine. Though this methodology might sound just like the egg-based methodology, rising the vaccine in cells permits for sooner manufacturing of the vaccine materials and isn’t a priority in sufferers with egg allergic reactions.7 As well as, the cell-based methodology additionally avoids the danger of egg-adapted modifications.8

The ultimate methodology of influenza vaccine manufacturing includes using recombinant expertise and was permitted to be used in 2013. CVVs are usually not utilized in one of these manufacturing. As a substitute, the producer makes use of viral DNA to supply hemagglutinin (HA), which is a floor receptor of the influenza virus that features as an antigen to elicit an immune response. The DNA is then integrated right into a baculovirus (a nonpathogenic virus) to create a recombinant virus. The recombinant virus is then mixed with an FDA-approved cell line, the place it offers directions for the cells to supply HA. As soon as produced, the HA is then purified and used to supply the recombinant influenza vaccine. This methodology of vaccine manufacturing is the quickest at present accessible and doesn’t require using eggs in any a part of the method.7 Moreover, because the vaccine materials shouldn’t be grown in eggs, egg-adapted modifications are usually not a priority when using the recombinant methodology.9

Normal Vs Excessive-Dose Vaccines

Most influenza formulations can be found as an ordinary dose. Nevertheless, as of 2009, a extra concentrated formulation has been developed as a high-dose possibility for sufferers at elevated threat of an infection (eg, those that are 65 and older). The high-dose formulation incorporates 4 occasions the quantity of antigen because the standard-dose preparations.10 The high-dose influenza vaccine is simply accessible as a quadrivalent formulation. All at present accessible influenza vaccine formulations will be present in Desk 2.11

Opposed Results and Contraindications for Flu Vaccines

Individuals who avoided receiving the COVID-19 vaccine due to evolving security knowledge may categorical the identical hesitancy towards the upcoming flu vaccines.12 Subsequently, you will need to reestablish the protection of vaccinations inside the public eye. Opposed results (AEs) to the annual flu vaccine are sometimes gentle and resolve rapidly. Mutual AEs are noticed within the inactivated and recombinant vaccines, together with soreness, redness, and ache on the injection website, in addition to muscle aches, nausea, fever, and complications.13 In keeping with the outcomes of a number of research, injection website ache was discovered to be extra frequent in quadrivalent doses, which will be attributed to the physique’s response to an extra antigen.14 Moreover, variations in systemic results have been established between youngsters and adults. Each teams reported headache and malaise; nevertheless, youngsters extra steadily skilled irritability, whereas fatigue was extra frequent in adults.14

Though dwell vaccines are related to extra pronounced AEs, a surveillance report of the dwell attenuated influenza vaccine (LAIV) quadrivalent dose extra generally recognized nonserious AEs corresponding to fever, cough, and headache.15 One vaccine, FluMist (AstraZeneca), elicits an immune response by replicating within the epithelial, mucosal cells of the nasopharynx.16 Consequently, nasal congestion, rhinorrhea, and sore throat are extra generally reported in folks receiving FluMist in contrast with these getting the inactivated and recombinant vaccines.16

Advisory Committee on Immunization Practices suggestions recommend the LAIV requires higher surveillance of affected person traits; nevertheless, the contraindications of all vaccines ought to be fastidiously thought of earlier than the administration of any dose.17 All of the accessible vaccines are contraindicated in folks with a historical past of allergic reactions to any element of the vaccine because of the threat of anaphylaxis. Most notably, folks with egg allergic reactions ought to keep away from any of the egg-based vaccines listed in Desk 2. The LAIV preparation is contraindicated in youngsters aged 2 to 4 years with bronchial asthma or wheezing inside the previous 12 months, concomitant aspirin- or salicylate-containing remedy, immunocompromised for any trigger, being pregnant, individuals with cochlear implants, and people who have obtained influenza antiviral medicines inside the previous 48 hours.17

Recommending a Flu Vaccine

The intent of receiving a flu vaccine annually is to stop extreme, life-threatening issues, hospitalizations, and loss of life from the virus.18 Every flu vaccine incorporates totally different elements and is manufactured in several methods, permitting pharmacists and sufferers to work collectively to find out the fitting vaccine to obtain. Two components to contemplate when recommending a vaccine for a affected person are patient-specific traits (eg, age and comorbid circumstances) and accuracy of the vaccine with the circulating flu viruses in the neighborhood.18 In sufferers older than 65 or who’ve weakened immune techniques, high-dose or adjuvanted quadrivalent vaccines have demonstrated increased efficacy over standard-dose trivalent vaccines.18 In youngsters, flu vaccine effectiveness has proven to be increased in those that obtained 2 doses of their first flu season in contrast with youngsters who obtained 1 dose.18 Finally, receiving a flu vaccine protects the recipient and members of the neighborhood, particularly extra susceptible populations, from results of the virus, cardiac occasions, and worsening of continual lung illness, and it additionally reduces hospitalizations in sufferers with diabetes and continual lung illness.18


The flu season. CDC. Up to date Could 6, 2021. Accessed Could 27, 2021. https://www.cdc.gov/flu/about/season/flu-season.htm

Influenza vaccination data for well being care staff. CDC. Up to date January 28, 2021. Accessed Could 13, 2021. https://www.cdc.gov/flu/professionals/healthcareworkers.htm#flu-facts

U.S. COVID-19 vaccine product data. CDC. Up to date March 2, 2021. Accessed June 8, 2021. https://www.cdc.gov/vaccines/covid-19/info-by-product/index.html



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