Influenza vaccines: where we are, where we are going

Background BNT162b2 is a lipid nanoparticle–formulated, nucleoside-modified RNA vaccine encoding a prefusion-stabilized, membrane-anchored severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) full-length spike protein. BNT162b2 is highly efficacious against coronavirus disease 2019 (Covid-19) and is currently approved, conditionally approved, or authorized for emergency use worldwide. At the time of initial authorization, data beyond 2 months after vaccination were unavailable. Methods In an ongoing, placebo-controlled, observer-blinded, multinational, pivotal efficacy trial, we randomly assigned 44,165 participants 16 years of age or older and 2264 participants 12 to 15 years of age to receive two 30-μg doses, at 21 days apart, of BNT162b2 or placebo. The trial end points were vaccine efficacy against laboratory-confirmed Covid-19 and safety, which were both evaluated through 6 months after vaccination. Results BNT162b2 continued to be safe and have an acceptable adverse-event profile. Few participants had adverse events leading to withdrawal from the trial. Vaccine efficacy against Covid-19 was 91.3% (95% confidence interval [CI], 89.0 to 93.2) through 6 months of follow-up among the participants without evidence of previous SARS-CoV-2 infection who could be evaluated. There was a gradual decline in vaccine efficacy. Vaccine efficacy of 86 to 100% was seen across countries and in populations with diverse ages, sexes, race or ethnic groups, and risk factors for Covid-19 among participants without evidence of previous infection with SARS-CoV-2. Vaccine efficacy against severe disease was 96.7% (95% CI, 80.3 to 99.9). In South Africa, where the SARS-CoV-2 variant of concern B.1.351 (or beta) was predominant, a vaccine efficacy of 100% (95% CI, 53.5 to 100) was observed. Conclusions Through 6 months of follow-up and despite a gradual decline in vaccine efficacy, BNT162b2 had a favorable safety profile and was highly efficacious in preventing Covid-19. (Funded by BioNTech and Pfizer; ClinicalTrials.gov number, NCT04368728 .)

After recognition of widespread community transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), by mid- to late February 2020, indicators of influenza activity began to decline in the Northern Hemisphere. These changes were attributed to both artifactual changes related to declines in routine health seeking for respiratory illness as well as real changes in influenza virus circulation because of widespread implementation of measures to mitigate transmission of SARS-CoV-2. Data from clinical laboratories in the United States indicated a 61% decrease in the number of specimens submitted (from a median of 49,696 per week during September 29, 2019–February 29, 2020, to 19,537 during March 1–May 16, 2020) and a 98% decrease in influenza activity as measured by percentage of submitted specimens testing positive (from a median of 19.34% to 0.33%). Interseasonal (i.e., summer) circulation of influenza in the United States (May 17–August 8, 2020) is currently at historical lows (median = 0.20% tests positive in 2020 versus 2.35% in 2019, 1.04% in 2018, and 2.36% in 2017). Influenza data reported to the World Health Organization’s (WHO’s) FluNet platform from three Southern Hemisphere countries that serve as robust sentinel sites for influenza from Oceania (Australia), South America (Chile), and Southern Africa (South Africa) showed very low influenza activity during June–August 2020, the months that constitute the typical Southern Hemisphere influenza season. In countries or jurisdictions where extensive community mitigation measures are maintained (e.g., face masks, social distancing, school closures, and teleworking), those locations might have little influenza circulation during the upcoming 2020–21 Northern Hemisphere influenza season. The use of community mitigation measures for the COVID-19 pandemic, plus influenza vaccination, are likely to be effective in reducing the incidence and impact of influenza, and some of these mitigation measures could have a role in preventing influenza in future seasons. However, given the novelty of the COVID-19 pandemic and the uncertainty of continued community mitigation measures, it is important to plan for seasonal influenza circulation in the United States this fall and winter. Influenza vaccination of all persons aged ≥6 months remains the best method for influenza prevention and is especially important this season when SARS-CoV-2 and influenza virus might cocirculate ( 1 ). Data from approximately 300 U.S. clinical laboratories located throughout all 50 states, Puerto Rico, Guam, and the District of Columbia that participate in virologic surveillance for influenza through either the U.S. WHO Collaborating Laboratories System or the National Respiratory and Enteric Virus Surveillance System* were used for this analysis. Clinical laboratories primarily test respiratory specimens for diagnostic purposes, and data from these laboratories provide useful information on the timing and intensity of influenza activity. The median number of specimens tested per week and the median percentage of samples testing positive for influenza during September 29, 2019–February 29, 2020 (surveillance weeks 40–9, the period before the March 1, 2020 declaration of a national emergency related to COVID-19 † ) were compared with those tested during March 1–May 16, 2020 (weeks 10–20 after the declaration); data from three previous influenza seasons are presented as a comparison. To assess influenza virus activity in the Southern Hemisphere, influenza laboratory data from clinical and surveillance platforms reported from Australia, Chile, and South Africa to WHO’s FluNet § platform were analyzed. For each country, the percentage of samples testing positive for influenza for April–July (weeks 14–31) for four seasons (2017–2020) are presented. Selected measures implemented to respond to COVID-19 in these countries were ascertained from government websites. All data used were in the public domain. In the United States, influenza activity (measured by percentage of respiratory specimens submitted for influenza testing that yielded positive results) began to increase in early November 2019, and >20% of specimens were positive during December 15, 2019–March 7, 2020 (weeks 51–10), after which activity declined sharply (Figure 1). Percent positivity peaked on week 6 at 30.25% and decreased 14.90% by week 9, compared with an 89.77% decrease during weeks 10–13. By the week of March 22, 2020 (week 13), when the number of samples tested remained very high, percent positivity dropped to 2.3%, and since the week of April 5, 2020 (week 15), has remained 20% to 2.3% and has remained at historically low interseasonal levels (0.2% versus 1–2%). Data from Southern Hemisphere countries also indicate little influenza activity. What are the implications for public health practice? Interventions aimed against SARS-CoV-2 transmission, plus influenza vaccination, could substantially reduce influenza incidence and impact in the 2020–21 Northern Hemisphere season. Some mitigation measures might have a role in reducing transmission in future influenza seasons.

Universal vaccination of children 6 to 59 months of age with trivalent inactivated influenza vaccine has recently been recommended by U.S. advisory bodies. To evaluate alternative vaccine approaches, we compared the safety and efficacy of intranasally administered live attenuated influenza vaccine with those of inactivated vaccine in infants and young children. Children 6 to 59 months of age, without a recent episode of wheezing illness or severe asthma, were randomly assigned in a 1:1 ratio to receive either cold-adapted trivalent live attenuated influenza vaccine (a refrigeration-stable formulation of live attenuated intranasally administered influenza vaccine) or trivalent inactivated vaccine in a double-blind manner. Influenza-like illness was monitored with cultures throughout the 2004-2005 influenza season. Safety data were available for 8352 children, and 7852 children completed the study according to the protocol. There were 54.9% fewer cases of cultured-confirmed influenza in the group that received live attenuated vaccine than in the group that received inactivated vaccine (153 vs. 338 cases, P<0.001). The superior efficacy of live attenuated vaccine, as compared with inactivated vaccine, was observed for both antigenically well-matched and drifted viruses. Among previously unvaccinated children, wheezing within 42 days after the administration of dose 1 was more common with live attenuated vaccine than with inactivated vaccine, primarily among children 6 to 11 months of age; in this age group, 12 more episodes of wheezing were noted within 42 days after receipt of dose 1 among recipients of live attenuated vaccine (3.8%) than among recipients of inactivated vaccine (2.1%, P=0.076). Rates of hospitalization for any cause during the 180 days after vaccination were higher among the recipients of live attenuated vaccine who were 6 to 11 months of age (6.1%) than among the recipients of inactivated vaccine in this age group (2.6%, P=0.002). Among young children, live attenuated vaccine had significantly better efficacy than inactivated vaccine. An evaluation of the risks and benefits indicates that live attenuated vaccine should be a highly effective, safe vaccine for children 12 to 59 months of age who do not have a history of asthma or wheezing. (ClinicalTrials.gov number, NCT00128167 [ClinicalTrials.gov].). Copyright 2007 Massachusetts Medical Society.