Estimating the Potential Effects of a Vaccine Program Against an Emerging Influenza Pandemic—United States

Abstract

Background Human illness from influenza A(H7N9) was identified March 2013, and candidate vaccine viruses were soon developed. To understand factors that may impact influenza vaccination programs, we developed a model to evaluate hospitalizations and deaths averted considering various scenarios. Methods We utilized a model incorporating epidemic curves with clinical attack rates of 20% or 30% in a single wave of illness, case hospitalization ratios of 0.5% or 4.2%, and case fatality ratios of 0.08% or 0.53%. We considered scenarios that achieved 80% vaccination coverage, various starts of vaccination programs (16 or 8 weeks before, the same week of, or 8 or 16 weeks after start of pandemic), an administration rate of 10 or 30 million doses/week (the latter rate is an untested assumption), and two levels of vaccine effectiveness (two doses of vaccine required; either 62% or 80% effective for persons aged <60, and either 43% or 60% effective for persons aged ≥60). Results The start date of vaccination campaigns most influenced impact; from 141,000 – 2,200,000 hospitalizations and 11,000 – 281,000 deaths were averted when campaigns started before a pandemic and <100 – 1,300,000 hospitalizations and 0 – 165,000 deaths were averted for programs beginning the same time as or after the introduction of the pandemic virus. The rate of vaccine administration and vaccine effectiveness did not influence campaign impact as much as timing of start of campaign. Conclusions Our findings suggest that efforts to improve the timeliness of vaccine production will provide the greatest impacts for future pandemic vaccination programs.

Influenza illness averted by influenza vaccination among school year children in Beijing, 2013‐2016

“…Our study suggested that VE has a strong impact on vaccination outcome, and a small improvement of VE will result in a significant reduction in cases. The timing of vaccination relative to disease occurrence also affects the benefit of vaccination . Comparing the 2014/15 season with the 2015/16 season, the fraction number was significantly lower in 2014/15, while the coverage rate and VE were higher in 2014/15.…”

“…In our study, the VC was similar over years, so the impact of VC was not evaluated. In the United States, CDC estimated the averted number of influenza‐associated outcomes by vaccination in consecutive seasons by age group, and the results suggested that a greater fraction of disease was prevented as greater fractions of the population were vaccinated . It is estimated that a 20% increase in VC among schoolchildren corresponds to an 8% decrease in emergency department visits .…”

“…We used prevented fraction to show the impact of vaccination policy. The index has been used by researches from CDC, and in a similar modeling study . Unlike absolute numbers of averted outcomes, which are associated with the influenza attack rate, the prevented fraction is mainly affected by VE and VC, making it a good method for evaluating impact of vaccination policy.…”

“…The timing of vaccination relative to disease occurrence also affects the benefit of vaccination. 14 Table 1. On the other hand, we noticed that in the 2014/15 season the influenza epidemic occurred earlier, meaning that vaccination occurred later relative to the onset of the season (Figure 2).…”

Distinct Effects of T-705 (Favipiravir) and Ribavirin on Influenza Virus Replication and Viral RNA Synthesis

“…In addition, zoonotic influenza A viruses of swine or avian species create a risk for pandemics, such as occurred in 2009 (3). Influenza vaccination is a highly effective preventive measure, yet it suffers from some limitations: unsatisfactory immune response in elderly or immunodeficient persons, poor efficacy in the case of vaccine mismatch, and a lag time of Ͼ6 months to prepare a novel vaccine in the case of a pandemic (4). Hence, antiviral drugs are indispensable as a complementary strategy to combat influenza virus infections.…”