Since the emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Wuhan, China, millions of lives have been lost, and ten times that number of patients have required hospitalization to successfully overcome the infection. Spreading rapidly across land and sea boundaries within days of onset, the virus hit New York City (NYC) especially hard.
A new study, released as a preprint on the medRxiv* server, shows how the successful rollout of effective COVID-19 vaccines in this metropolis led to the dramatic reduction in the number of cases with moderate to severe coronavirus disease 2019 (COVID-19) and curbed related-COVID-19 mortality.
The virus entered NYC via many different introductions, with the first case being reported on February 29, 2020, and rapidly began to spread through the community. Two months later, the city was reeling under a flood of over 100,000 cases, which made up one in five of all American cases, and about 7% of cases globally. NYC had become the new epicenter of the pandemic.
The unprecedented speed with which the earliest vaccines were developed and presented for emergency use authorizations led to the first vaccination shot in NYC being administered as early as December 2020. By July 2021, almost 70% of adults living in the city have received at least one dose of a COVID-19 vaccine. Approximately two in three have been fully vaccinated.
Gratifyingly, this achievement has been accompanied by a steep drop in cases from over 5,500 daily, in January 2020, to below 350 a day in July 2021. To put this in context, it should be noted that the currently circulating dominant strains of the virus, such as the alpha, gamma and delta strains (B.1.1.7, P.1 and B.1.617.2, respectively), are highly transmissible.
Reduced severe and fatal outcomes
The current study is a pioneering attempt to provide a formal evaluation of the effect of vaccination on COVID-19 hospitalizations and mortality. The researchers used an agent-based model, stratified by age, including the transmission profile of the above strains.
Incorporating the demographic, age-dependent odds of adverse outcomes, contact patterns and the known natural history of the infection, the scientists modeled a priming-booster dose vaccine regimen with age-dependent prioritization following real-life criteria. The resulting vaccine allocation and administration mimicked the actual NYC performance.
The results showed that an estimated 250,000 cases of COVID-19 were averted, out of which approximately 44,000 would have required hospitalization. There were 8,300 fewer deaths. When compared to the estimated 851,000 infections that would otherwise have happened, with approximately 87,000 requiring hospital admission and an estimated 17,200 having a fatal outcome, this corresponds to 30% fewer cases following vaccination. The number of hospitalizations dropped to about half, as did the number of deaths.
Why do COVID-19 hospitalizations and deaths decrease more than cases?
The increased efficacy of the vaccine against symptomatic COVID-19 was expected to bring about precisely this outcome, with the reduction in deaths and severe symptoms being more marked than the drop in the number of cases. This feature is also expected to allow the transmission to continue despite vaccination, though the extent may be restricted by the reduction in viral load.
The prioritization of frontline healthcare workers, as well as of the elderly and sick, also contributed to this imbalance in case reduction vs. symptomatic/severe illness reduction, since these groups were at unduly high risk for severe or critical COVID-19.
The alpha variant rapidly rose to dominance first in the UK and then throughout the world. Without vaccination, this variant might have led to almost a thousand hospitalizations per day, with a peak mortality of about 200 deaths in April 2021. In passing, it is important to note that both hospitalizations and deaths in April were twice as high as the monthly peak in January 2021.
The delta variant is highly transmissible, and was expected to fuel a fresh surge of severe cases and deaths as it rose towards the dominant place, beginning in May. However, though cases increased over June and still further in July, the average daily incidence is lower than before.
Yet, the most important end result of the rapid pace of prioritized vaccination in NYC is the suppression of “another wave of COVID-19 that would have led to sustained increase in cases, hospitalizations and deaths during spring triggered by highly transmissible variants.”
What are the implications?
The key role played by vaccines in preventing a high burden of COVID-19 is obvious from the findings of this study. Moreover, rapid vaccination coverage suppressed other potential outbreaks due to the higher tendency to spread of the delta and other more infective variants.
Most importantly, despite high vaccination rates, the delta wave is overtaking NYC, with three times as many cases being recorded in July as in May. This indicates that there are important gaps in vaccine coverage persisting despite the vaccination drive.
This highlights the continued need to expand vaccination as well as focusing on underserved neighbourhoods and communities with a low-vaccination coverage to achieve outbreak control and maximize protection against future variants.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.