Multiple COVID-19 Waves and Vaccination Effectiveness in the United States

Abstract

(1) Background: The coronavirus 2019 (COVID-19) pandemic has caused multiple waves of cases and deaths in the United States (US). The wild strain, the Alpha variant (B.1.1.7) and the Delta variant (B.1.617.2) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were the principal culprits behind these waves. To mitigate the pandemic, the vaccination campaign was started in January 2021. While the vaccine efficacy is less than 1, breakthrough infections were reported. This work aims to examine the effects of the vaccination across 50 US states and the District of Columbia. (2) Methods: Based on the classic Susceptible—Exposed—Infectious–Recovered (SEIR) model, we add a delay class between infectious and death, a death class and a vaccinated class. We compare two special cases of our new model to simulate the effects of the vaccination. The first case expounds the vaccinated individuals with full protection or not, compared to the second case where all vaccinated individuals have the same level of protection. (3) Results: Through fitting the two approaches to reported COVID-19 deaths in all 50 US states and the District of Columbia, we found that these two approaches are equivalent. We calculate that the death toll could be 1.67–3.33 fold in most states if the vaccine was not available. The median and mean infection fatality ratio are estimated to be approximately 0.6 and 0.7%. (4) Conclusions: The two approaches we compared were equivalent in evaluating the effectiveness of the vaccination campaign in the US. In addition, the effect of the vaccination campaign was significant, with a large number of deaths averted.

Reduction in the infection fatality rate of Omicron variant compared with previous variants in South Africa

“…We fit our previously proposed Susceptible-Exposed-Infectious-Hospitalized-Death-Recovered-Vaccinated model to the observed case and death data in South Africa ( Lin et al, 2021 ;Lin et al, 2022 ). We assumed that a proportion (denoted as ρ) of the infections was reported and that ρ < 7%.…”

Impact of vaccine hesitancy on secondary COVID-19 outbreaks in the US: an age-structured SIR model

“…Then, a new outbreak is seeded in each state, emulating a spill over from other states in the country or importation from other countries. In this second outbreak, we set which is closer to the dominant variant of concern (delta variant) [ 50 ], predominant in the US since mid 2021 until the emergence of the Omicron strain by the end of 2021 [ 51 , 52 ], being this last variant of concern more highly transmissible with respect to Delta even though with lower pathogenicity [ 53 ]. The reason to propose these secondary outbreaks in each US state with an more in line with Delta is the availability of data to compare our hypothetical scenario with reality.…”

COVID-19 waves: variant dynamics and control

“…The major waves of COVID-19 infections, after the initial onset, are largely caused by the emerging variants of concern 1 . They prolong the persistence of infections inflicting loss to human lives, economies and continue to strain the public health infrastructure 2 .…”