25 Nov COVID: Israeli Study Finds Immunity After Two Vaccine Doses Wanes with Time
MedicalResearch.com Interview with:
Ariel Israel, M.D., Ph.D.
Director, Leumit Health Services
Tel Aviv, Israel
MedicalResearch.com: What is the background for this study?
Response: As a research institute of Leumit, one of the four state mandated health funds in Israel, we pursue research projects aimed at improving the health of our members, and reducing the burden of disease. For this purpose, we harness the unique resource of the electronic health records of our members, that is available in a central data warehouse for research purposes.
Israel was one of the first countries to roll-out a large-scale vaccination campaign, and to achieve control of the pandemics through vaccination. Nevertheless, since the middle of June ’21, we have observed a gradual increase in the rate of COVID-19 infections among our members, even among the vaccinated. This increase was first believed to be due to the emergence of the delta strain, but when we compared vaccinated individuals who suffered from breakthrough infections to other vaccinated individuals, we found that the time that has elapsed since vaccination was significantly longer for individuals who got infected with COVID-19, in each of the age groups.
This prompted us to investigate the issue of a possible waning effect of the vaccine protection with time, that we present in this report, using the test negative study design.
We examined the electronic health records for 80,057 adults (average age 44 years) who received a PCR test at least three weeks after their second injection, and had no evidence of previous covid-19 infection. Of these 80,057 participants, 7,973 (9.6%) had a positive test result. These individuals were then matched to negative controls of the same age and ethnic group who were tested in the same week.
MedicalResearch.com: What are the main findings?
Response: The rate of positive results increased with time elapsed since a second dose. For example, across all age groups 1.3% of participants tested positive 21-89 days after a second dose, but this increased to 2.4% after 90-119 days; 4.6% after 120-149 days; 10.3% after 150-179 days; and 15.5% after 180 days or more.
After taking account of other potentially influential factors, we found a significantly increased risk of infection with time elapsed since a second dose:
- Compared with the initial 90 days after a second dose, the risk of infection across all age groups was 2.37-fold higher after 90-119 days;
- 2.66-fold higher after 120-149 days; 2.82-fold higher after 150-179 days;
- and 2.82-fold higher after 180 days or more.
MedicalResearch.com: Does this report support the need for vaccine boosters?
Response: Yes, this study shows that the protection provided by two injections of the Pfizer vaccine wanes with time. Our results were presented to the Ministry of Health Covid-19 committee, which in part based on our reports, recommended a booster dose, first for individuals aged 60 or more, and then for all the population.
The third booster dose quickly helped to reduce the infection rate, and to curb the infection wave.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: Most of our population is now vaccinated with three injections, and we observe that the infection rate is significantly reduced among individuals who had received three injections
The question is now how long would the protection provided by three injections last. For this purpose,
we continue to monitor the infection rate with time since vaccination in our population.
MedicalResearch.com: Is there anything else you would like to add?
Response: This study was performed in collaboration with the Cancer Data Science Lab in the National Cancer Institute, NIH, and we hope to extend this collaboration with other studies based on our patients database.
Investigators from this study have not received any support from vaccine manufacturers or affiliates that could constitute a potential conflict of interest.
Elapsed time since BNT162b2 vaccine and risk of SARS-CoV-2 infection: test negative design study
BMJ 2021;375:e067873 http://dx.doi.org/10.1136/ bmj-2021-067873 Accepted: 2 November 2021
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