Study: Covid-19 Vaccine Effectiveness in New York State. Image Credit: Ivan Marc/Shutterstock
Scientists have claimed that the development of effective vaccines and rapid vaccination programs are the foremost measures to manage the COVID-19 pandemic. In the US, three vaccines have received emergency use authorization (EUA) from the Food and Drug Administration (FDA) and all these vaccines have reported high efficacy against moderate-to-severe disease among adults. COVID-19 vaccines that have received EUA in the US have been developed by Pfizer–BioNTech, Moderna, and Johnson & Johnson–Janssen.
The evolution of the SARS-CoV-2 virus, due to mutations, has threatened the efficacy of the available vaccines. The circulating SARS-CoV-2 Delta variant has been characterized to be more transmissible and virulent compared to the original SARS-CoV-2 strain. Also, this virus can evade immune responses induced by vaccines or natural SARS-CoV-2 infection.
Studies on the real-world effectiveness of the vaccines revealed that the efficacy of vaccines decline over time. Compared to the US reports, studies in Israel have shown that individuals who received the BNT162b2 vaccine experienced a greater decrease in immune protection against severe disease as well as infection. This difference in immune response may be because the vaccination program started in Israel much earlier than in the US.
At the time when the mitigation measures were relaxed and the Delta variant became dominant, population-based studies conducted in New York showed a decrease in vaccine effectiveness with time, especially, for individuals who were above 65 years. However, one of the major limitations of these controlled, open cohort surveillance studies was the difficulty in determining the major cause for the decrease in vaccine effectiveness. These studies could not predict if the decline in the vaccine effectiveness occurred owing to waning immunity, the emergence of the Delta variant, behavioral changes among persons, etc.
Scientists claim that more data are required to comprehend the extent and sources of changes in vaccine effectiveness with respect to disease outcomes, type of vaccine, and population subgroups. These data will help researchers appropriately recommend COVID-19 vaccines to public health policymakers.
Recently, after authorization was granted by the FDA, the Centres for Disease Control and Prevention (CDC) recommended booster doses of COVID-19 vaccines to various groups of individuals, e.g., individuals who are of or above 65 years of age, individuals with underlying conditions, and frontline workers who are at a high risk of contracting the infection. These recommendations were made despite having a gap in data from the US regarding the effectiveness of the COVID-19 vaccine across various age groups, times of vaccination, and product.
A new study
Researchers have recently conducted a state-wide, surveillance-based, prospective cohort study to determine vaccine effectiveness among adults in New York State. This study is published in the New England Journal of Medicine. Scientists have defined this study cohort according to the age of the recipient, time of vaccination, and vaccine product from the time of the emergence of the SARS-CoV-2 Delta strain until it became the dominant circulating strain.
This study used data for 8,690,825 adults in New York State to determine the effectiveness of three vaccines, i.e., BNT162b2, mRNA-1273, and Ad26.COV2. S, against confirmed COVID-19 infection and hospitalization.
The main findings
Scientists observed a declining trend in vaccine effectiveness from May through August 2021. This decrease was found to be inversely correlated with the increasing prevalence of the Delta variant. This decrease was prevalent across all age groups, and time cohorts. The largest decline was reported among the recipients of the BNT162b2 vaccine.
The effectiveness of the vaccines against hospitalization with SARS-CoV-2 infection remained high. However, a decreased vaccine effectiveness was reported among individuals who were 65 years of age or above and those who received Ad26.COV2.S. A marginal decline of vaccine effectiveness was reported among the recipients (65 years of age and above) of BNT162b2 and mRNA-1273 vaccines.
The main strength of this study is the use of closed cohorts that helped minimize the challenges posed by previous surveillance-based approaches. The large sample size is another strength of this study. Scientists indicated that when New York State relaxed the use of reduced facemask, social distancing, and other prevention practices, there was an increase in the exposure among vaccinated individuals which might be the reason for lowered vaccine effectiveness. However, the effectiveness improved with the increased use of facemasks.
The authors of this study reported that irrespective of the cause for continued declines in vaccine effectiveness, BNT162b2 booster doses have been found to be safe and have shown enhancement in short-term protection against the Delta variant. Further, this study stated that continual use of non-pharmaceutical measures along with vaccines would effectively protect individuals from COVID-19 disease.