The 2020-2021 influenza season is shaping up to be challenging. Its likely concurrence with the ongoing severe acute respiratory syndrome-coronavirus 2 (SARS-coV-2) pandemic (COVID-19) will pose diagnostic and therapeutic dilemmas and could overload the hospital system. But there could also be potential synergies in preventing morbidity and mortality from each disease.
A consistent pattern overthe past few influenza seasons
During the 2019-2020 flu season, there were an estimated 410,000 to 740,000 hospitalizations and 24,000 to 62,000 deaths attributed to influenza.1 As seen in FIGURE 1, office visits for influenza-like illness (ILI) began to increase in late November and early December in each of the last 3 years (2017-2018, 2018-2019, 2019-2020) and stayed elevated above baseline for about 4 months each season.1
The effectiveness of influenza vaccine during the 2019-2020 season is being estimated using the US Flu Vaccine Effectiveness Network, which has close to 9000 enrollees. Overall, it appears the vaccine was 39% effective against medically attended influenza, with a higher effectiveness against influenza B (44%) than against A/H1N1 (31%). Effectiveness against influenza B was similar in all age groups, but effectiveness against A/H1N1 was highest for those ages 50 to 64 years (45%) and lowest for those ages 6 months through 8 years (22%), although 95% confidence intervals overlapped for all age groups (FIGURE 2). These preliminary effectiveness rates were presented at the summer meeting of the Advisory Committee on Immunization Practices (ACIP).1
Influenza vaccine safety data for 2019-2020 were based on the Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system, and on the Vaccine Safety Datalink (VSD) system, an active surveillance system involving close to 6 million doses administered at VSD sites. No safety concerns were identified for any of the different vaccine types. Both the VAERS and VSD surveillance systems have been described in more detail in a previous Practice Alert.2
Recommendations for 2020-2021
The composition of the influenza vaccines for this year’s flu season will be different for 3 of the 4 antigens: A/H1N1, A/H2N2 and B/Victoria.3 The antigens included in the influenza vaccines each year are decided on in the spring, based on surveillance of circulating strains around the world. The effectiveness of the vaccine each year largely depends on how well the strains included in the vaccine match those circulating in the United States during the influenza season.
The main immunization recommendation for preventing morbidity and mortality from influenza has not changed: All individuals ages 6 months and older without a contraindication should receive an influenza vaccine.4 The Centers for Disease Control and Prevention (CDC) recommends that patients receive the vaccine by the end of October.4 This includes the second dose for those children younger than 9 years who need 2 doses—ie, those who have received fewer than 2 doses of influenza vaccine prior to July 2020. Vaccination should continue through the end of the season for anyone who has not received a 2020-2021 influenza vaccine.
Two new influenza vaccine products are available for use in those ages 65 years and older: Fluzone high-dose quadrivalent and Fluad Quadrivalent (adjuvanted).4 Both of these products were available last year as trivalent options. Currently no specific vaccine product is listed as preferred by ACIP for those ages 65 and older.
Continue to: New vaccine contraindications