Vaccine update for the 2022-23 influenza season

In the 2020-2021 influenza season, there was practically no influenza circulating in the United States. This decline from seasonal expectations, described in a previous Practice Alert, was probably due to the interventions aimed at limiting the spread of ­COVID-19: masking, social distancing, working from home, and cancellation of large, crowded events.¹ In 2021-2022 influenza returned, but only in moderation.

The Centers for Disease Control and Prevention (CDC) estimates there were between 82,000 to 170,000 hospitalizations and 5000 to 14,000 deaths attributed to influenza.² In addition, US virologic surveillance indicates that 98.6% of specimens tested positive for influenza A.² While the vaccine’s effectiveness in 2021-2022 was far below what was desired, it still prevented a great deal of flu morbidity and mortality and reduced acute respiratory illness due to influenza A(H3N2) virus by 35% (TABLE 1).³ All vaccines for the upcoming flu season are quadrivalent, containing 2 influenza A antigens and 2 influenza B antigens (TABLES 2⁴ and 3⁵).

Vaccine effectiveness in older adults (≥ 65 years) has been very low. TABLE 4⁶ shows vaccine effectiveness in the elderly for 10 influenza seasons between 2011 and 2020.⁶ In nearly half of those seasons, the estimated vaccine effectiveness was possibly nil. All influenza vaccines licensed for use in the United States are approved for use in those ≥ 65 years of age, except live attenuated influenza vaccine (LAIV).

Three products were developed to address the issue of low vaccine effectiveness in the elderly. The Advisory Committee on Immunization Practices (ACIP) has not expressed a preference for any specific vaccine for this age group. The high-dose qudrivalent vaccine (HD-IIV4), Fluzone, contains 4 times the antigen level of the standard-dose vaccines (SD-IIV4)—60 μg vs 15 μg. Fluzone was initially approved in 2014 as a trivalent vaccine and was approved as a quadrivalent vaccine in 2019. The adjuvanted quadrivalent influenza vaccine (aIIV4), Fluad, was also inititally approved as a trivalent vaccine in 2015 and as quadrivalent in 2021. Both HD-IIV4 and aIIV4 are approved only for those ≥ 65 years of age. Recombinant quadrivalent influenza vaccine (RIV4), Flublok, is approved for ages ≥ 18 years and is produced by a process that does not involve eggs. It contains 3 times the antigen level as SD-IIV4 vaccines.

All 3 of these vaccines (HD-IIV4, aIIV4, and RIV4) have been compared with SD-IIV4 for effectiveness in the elderly and have yielded better outcomes. However, direct comparisons among the 3 vaccines have not shown robust evidence of superiority, and ACIP is unwilling to preferentially recommend one of them at this time. At its June 2022 meeting, ACIP voted to recommend any of these 3 options over the SD-IIV 4 options for those ≥ 65 years of age, with the caveat that if only an SD-IIV4 option is available it should be administered in preference to delaying vaccination.

One other vaccine change for the upcoming season involves the cell culture–based quadrivalent inactivated influenza vaccine (ccIIV4), Flucelvax, which is now approved for those ages ≥ 6 months. It previously was approved only for ages ≥ 2 years. All unadjuvanted SD-IIV4 vaccines as well as ccIIV4 are now approved for everyone ≥ 6 months of age. LAIV continues to be approved for ages 2 through 49 years. The only influenza vaccine products that contain thimerosal are those in multidose vials (TABLE 2⁴).

Promote vaccination and infection-control practices. ACIP continues to recommend influenza vaccine for all those ages ≥ 6 months, with 2 doses for those < 9 years old not previously vaccinated with an influenza vaccine. In addition to encouraging and offering influenza vaccine to patients and staff, we can minimize the spread of influenza in the community by robust infection-control practices in the clinical setting: masking and isolation of patients with respiratory symptoms, encouraging those with symptoms to stay at home and mask when around family members, advising frequent hand washing and respiratory hygiene, and using pre- and post-exposure chemoprophylaxis as appropriate. All recommendations regarding influenza for 2022-2023 can be found on the CDC website.⁴

In the 2020-2021 influenza season, there was practically no influenza circulating in the United States. This decline from seasonal expectations, described in a previous Practice Alert, was probably due to the interventions aimed at limiting the spread of ­COVID-19: masking, social distancing, working from home, and cancellation of large, crowded events.¹ In 2021-2022 influenza returned, but only in moderation.

The Centers for Disease Control and Prevention (CDC) estimates there were between 82,000 to 170,000 hospitalizations and 5000 to 14,000 deaths attributed to influenza.² In addition, US virologic surveillance indicates that 98.6% of specimens tested positive for influenza A.² While the vaccine’s effectiveness in 2021-2022 was far below what was desired, it still prevented a great deal of flu morbidity and mortality and reduced acute respiratory illness due to influenza A(H3N2) virus by 35% (TABLE 1).³ All vaccines for the upcoming flu season are quadrivalent, containing 2 influenza A antigens and 2 influenza B antigens (TABLES 2⁴ and 3⁵).

Vaccine effectiveness in older adults (≥ 65 years) has been very low. TABLE 4⁶ shows vaccine effectiveness in the elderly for 10 influenza seasons between 2011 and 2020.⁶ In nearly half of those seasons, the estimated vaccine effectiveness was possibly nil. All influenza vaccines licensed for use in the United States are approved for use in those ≥ 65 years of age, except live attenuated influenza vaccine (LAIV).

Three products were developed to address the issue of low vaccine effectiveness in the elderly. The Advisory Committee on Immunization Practices (ACIP) has not expressed a preference for any specific vaccine for this age group. The high-dose qudrivalent vaccine (HD-IIV4), Fluzone, contains 4 times the antigen level of the standard-dose vaccines (SD-IIV4)—60 μg vs 15 μg. Fluzone was initially approved in 2014 as a trivalent vaccine and was approved as a quadrivalent vaccine in 2019. The adjuvanted quadrivalent influenza vaccine (aIIV4), Fluad, was also inititally approved as a trivalent vaccine in 2015 and as quadrivalent in 2021. Both HD-IIV4 and aIIV4 are approved only for those ≥ 65 years of age. Recombinant quadrivalent influenza vaccine (RIV4), Flublok, is approved for ages ≥ 18 years and is produced by a process that does not involve eggs. It contains 3 times the antigen level as SD-IIV4 vaccines.

All 3 of these vaccines (HD-IIV4, aIIV4, and RIV4) have been compared with SD-IIV4 for effectiveness in the elderly and have yielded better outcomes. However, direct comparisons among the 3 vaccines have not shown robust evidence of superiority, and ACIP is unwilling to preferentially recommend one of them at this time. At its June 2022 meeting, ACIP voted to recommend any of these 3 options over the SD-IIV 4 options for those ≥ 65 years of age, with the caveat that if only an SD-IIV4 option is available it should be administered in preference to delaying vaccination.

One other vaccine change for the upcoming season involves the cell culture–based quadrivalent inactivated influenza vaccine (ccIIV4), Flucelvax, which is now approved for those ages ≥ 6 months. It previously was approved only for ages ≥ 2 years. All unadjuvanted SD-IIV4 vaccines as well as ccIIV4 are now approved for everyone ≥ 6 months of age. LAIV continues to be approved for ages 2 through 49 years. The only influenza vaccine products that contain thimerosal are those in multidose vials (TABLE 2⁴).

Promote vaccination and infection-control practices. ACIP continues to recommend influenza vaccine for all those ages ≥ 6 months, with 2 doses for those < 9 years old not previously vaccinated with an influenza vaccine. In addition to encouraging and offering influenza vaccine to patients and staff, we can minimize the spread of influenza in the community by robust infection-control practices in the clinical setting: masking and isolation of patients with respiratory symptoms, encouraging those with symptoms to stay at home and mask when around family members, advising frequent hand washing and respiratory hygiene, and using pre- and post-exposure chemoprophylaxis as appropriate. All recommendations regarding influenza for 2022-2023 can be found on the CDC website.⁴

In the 2020-2021 influenza season, there was practically no influenza circulating in the United States. This decline from seasonal expectations, described in a previous Practice Alert, was probably due to the interventions aimed at limiting the spread of ­COVID-19: masking, social distancing, working from home, and cancellation of large, crowded events.¹ In 2021-2022 influenza returned, but only in moderation.

The Centers for Disease Control and Prevention (CDC) estimates there were between 82,000 to 170,000 hospitalizations and 5000 to 14,000 deaths attributed to influenza.² In addition, US virologic surveillance indicates that 98.6% of specimens tested positive for influenza A.² While the vaccine’s effectiveness in 2021-2022 was far below what was desired, it still prevented a great deal of flu morbidity and mortality and reduced acute respiratory illness due to influenza A(H3N2) virus by 35% (TABLE 1).³ All vaccines for the upcoming flu season are quadrivalent, containing 2 influenza A antigens and 2 influenza B antigens (TABLES 2⁴ and 3⁵).

Vaccine effectiveness in older adults (≥ 65 years) has been very low. TABLE 4⁶ shows vaccine effectiveness in the elderly for 10 influenza seasons between 2011 and 2020.⁶ In nearly half of those seasons, the estimated vaccine effectiveness was possibly nil. All influenza vaccines licensed for use in the United States are approved for use in those ≥ 65 years of age, except live attenuated influenza vaccine (LAIV).

Three products were developed to address the issue of low vaccine effectiveness in the elderly. The Advisory Committee on Immunization Practices (ACIP) has not expressed a preference for any specific vaccine for this age group. The high-dose qudrivalent vaccine (HD-IIV4), Fluzone, contains 4 times the antigen level of the standard-dose vaccines (SD-IIV4)—60 μg vs 15 μg. Fluzone was initially approved in 2014 as a trivalent vaccine and was approved as a quadrivalent vaccine in 2019. The adjuvanted quadrivalent influenza vaccine (aIIV4), Fluad, was also inititally approved as a trivalent vaccine in 2015 and as quadrivalent in 2021. Both HD-IIV4 and aIIV4 are approved only for those ≥ 65 years of age. Recombinant quadrivalent influenza vaccine (RIV4), Flublok, is approved for ages ≥ 18 years and is produced by a process that does not involve eggs. It contains 3 times the antigen level as SD-IIV4 vaccines.

All 3 of these vaccines (HD-IIV4, aIIV4, and RIV4) have been compared with SD-IIV4 for effectiveness in the elderly and have yielded better outcomes. However, direct comparisons among the 3 vaccines have not shown robust evidence of superiority, and ACIP is unwilling to preferentially recommend one of them at this time. At its June 2022 meeting, ACIP voted to recommend any of these 3 options over the SD-IIV 4 options for those ≥ 65 years of age, with the caveat that if only an SD-IIV4 option is available it should be administered in preference to delaying vaccination.

One other vaccine change for the upcoming season involves the cell culture–based quadrivalent inactivated influenza vaccine (ccIIV4), Flucelvax, which is now approved for those ages ≥ 6 months. It previously was approved only for ages ≥ 2 years. All unadjuvanted SD-IIV4 vaccines as well as ccIIV4 are now approved for everyone ≥ 6 months of age. LAIV continues to be approved for ages 2 through 49 years. The only influenza vaccine products that contain thimerosal are those in multidose vials (TABLE 2⁴).

Promote vaccination and infection-control practices. ACIP continues to recommend influenza vaccine for all those ages ≥ 6 months, with 2 doses for those < 9 years old not previously vaccinated with an influenza vaccine. In addition to encouraging and offering influenza vaccine to patients and staff, we can minimize the spread of influenza in the community by robust infection-control practices in the clinical setting: masking and isolation of patients with respiratory symptoms, encouraging those with symptoms to stay at home and mask when around family members, advising frequent hand washing and respiratory hygiene, and using pre- and post-exposure chemoprophylaxis as appropriate. All recommendations regarding influenza for 2022-2023 can be found on the CDC website.⁴