A study currently available on the preprint server medRxiv * has shown that the incidence and mortality rates of coronavirus disease 2019 (COVID-19) in the USA can be reduced significantly by increasing vaccination rates from 40% to 80% . An increased vaccination rate has a protective effect on the entire population, not just on the vaccinated.
background
The COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has severely impacted the economies and health systems of many countries, with more than 256 million infections and over 5.1 million deaths worldwide. The highest incidence and mortality were observed in the US with over 47 million infections and more than 768,000 deaths on November 19, 2021.
The US mass vaccination campaign includes three vaccines, namely BNT162b2 (Pfizer / BioNTech), mRNA 1273 (Moderna) and JNJ-78436735 (Janssen Pharmaceuticals). All of these vaccines have shown high efficacy in preventing SARS-CoV-2 infections, symptomatic COVID-19, hospitalizations, and death.
Despite high vaccine efficacy, a significant portion of the US population, especially minorities, remains unvaccinated due to reluctance to vaccinate. Such a decrease in vaccination coverage may affect the ability to achieve herd immunity and increase the incidence and mortality of COVID-19 at the population level.
In the current study, scientists from the UCLA Fielding School of Public Health, the International Vaccine Institute, the UCLA Fielding School of Public Health, and the UCLA School of Medicine looked at whether the community-wide spread of COVID-19 and associated mortality could be through an increase in the vaccination rate can be prevented.
Study design
The study examined the association between district-level vaccination rates and COVID-19 incidence and mortality using negative binomial models. The COVID-19 incidence and mortality data were obtained from the Center for Systems Science and Engineering Coronavirus Resource Center at Johns Hopkins University.
The study included a total of 3,070 counties in 49 US states, and the data was collected between April and September 2021. In addition, the study covered the period when the delta variant of SARS-CoV-2 became predominant in the United States (July). – September 2021).
A two-week interval between vaccination and full protection was considered to assess the effect of vaccination rate on COVID-19 incidence. Similarly, a four-week interval was introduced to assess the impact of vaccination rate on COVID-19 mortality.
Important observations
In 3,070 counties included in the analysis, the average vaccination rate at the population level was 42%. Compared to counties with less than 40% vaccination rates, counties with more than 40% vaccination rates had a higher number of hospital beds, a higher socio-economic status, a higher population density and a smaller uninsured population.
Overall, the study results showed that nationwide COVID-19 incidence and mortality rates could be reduced by 0.9% and 1.8%, respectively, by simply increasing the county-level vaccination rate by 1%.
A separate set of analyzes was carried out with the data collected between July and September 2021, when the delta variant was predominant in the USA. The results showed a positive association between the vaccination rate at the county level and protection against COVID-19.
Counties with more than 40% vaccination protection
Vaccination rates of more than 40% were found in 1,686 counties. In these counties, a 1% increase in vaccination rates was found to reduce COVID-19 incidence and mortality by 1.5% and 2.7%, respectively.
In contrast, in counties with vaccination coverage less than 40%, no association was observed between induction of vaccination rate and reductions in COVID-19 incidence and mortality.
The sensitivity analysis, which was conducted to assess the effects of gradually increasing the vaccination rate by 10%, found that 45% of COVID-19 cases and 67% of COVID-19-related deaths were caused by a 40% increase in vaccination rates at the district level. could have been prevented. to 80%.
Given the US population at risk, an estimated 5,989,952 COVID-19 cases and 127,596 deaths could have been prevented by increasing the vaccination rate from 40% to 80%.
Study significance
The study underscores the importance of the COVID-19 vaccination in reducing SARS-CoV-2 infection rates and the associated mortality. Specifically, the study results show that a significant level of protection against COVID-19 can be achieved in the USA by achieving a vaccination rate at the district level of 80%.
These results suggest that high vaccination coverage could provide population-wide protection from COVID-19, even if a significant portion of the population remains unvaccinated due to reluctance to vaccinate.
*Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, that guide clinical practice / health-related behavior or are treated as established information.
