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As of August 6, 2021, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is the virus responsible for 2019 coronavirus disease (COVID-19), has infected more than 201 million people and caused death of nearly 4.3 million worldwide.
The high transmissibility and unpredictable nature of SARS-CoV-2 has supported the rapid development of several COVID-19 vaccines that have already been distributed in many countries around the world. To date, nearly 30% of the world’s population has received at least one dose of a COVID-19 vaccine.
The recent increase in COVID-19 cases
After national approval of the Pfizer-BioNTech BNT162b2 vaccine, Israel quickly became one of the first countries to launch a large-scale vaccination campaign. Despite the fact that nearly 11.5 million doses of the COVID-19 vaccine have been administered across Israel, there has been a resurgence of SARS-CoV-2 cases in that country.
The increase in SARS-CoV-2 cases in Israel, as well as in many other countries around the world, requires a better understanding of how immune protection against SARS-CoV-2 can weaken over time. in vaccinated individuals and those recovering with HIV, such as from a previous infection with SARS-CoV-2. To this end, a recent study published on the preprint server medRxiv * determines whether the time since the second dose of BNT162b2 vaccine is associated with an increased risk of SARS-CoV-2 infection.
About the study
The present study is a retrospective cohort study based on data collected from Leumit Health Services (LHS), which is a major healthcare provider in Israel. The cohort included 33,993 people who had received a reverse transcriptase polymerase chain reaction (RT-PCR) test between May 15, 2021 and July 26, 2021, at least two weeks after receiving their second dose of the COVID-19 vaccine. .
To reflect the stages of vaccine deployment, the researchers included three age groups in the study, which included people aged 60 or older, 40 to 59, and 18 to 39. Importantly, at the time of their RT-PCR test, none of the study participants had evidence of a previous infection with COVID-19.
Study results
The median time between when participants received the second dose of the COVID-19 vaccine and received an RT-PCR test was 146 days. However, more than 50% of participants had received an RT-PCR test more than 146 days since their second dose.
Using 146 days as the deadline, the researchers found that in the 60 and over age group, 2.19% of those vaccinated were positive for SARS-CoV-2. Comparatively, the positivity rate in the 40-59 and 18-39 age groups was 1.93% and 1.39%, respectively. Overall, the increase in SARS-CoV-2 infection rates in all patient populations was significant.
Notably, at the time of the study, the dominant circulating variant was the SARS-CoV-2 Delta B.1.617.2 variant. Of the 113 isolates that were sent for sequencing in this study, 93% tested positive for the Delta variant.
Conclusion
While the incidence of SARS-CoV-2 infections was significant in all age groups, the largest increase was seen in patients aged 60 years and older. These results therefore support the concept that the immune response to vaccines is influenced by age-related changes in the immune system.
Since Israel was one of the first countries to launch a large-scale national vaccination campaign, most of the participants in this study received their second dose of the BNT162b2 vaccine at least six months before the study was conducted. . The results described here therefore demonstrate the decrease in protection offered by COVID-19 vaccines over time from the time the individual has received their second dose. This study also provides information on the protection offered by the BNT162b2 vaccine against the SARS-CoV-2 Delta strain which is now dominant in the world.
*Important Notice
medRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.
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