Massive vaccination programs around the world have resulted in significant protection against SARS-CoV-2 infection and serious disease. However, there has been an increase in innovative infections in late 2021 and early 2022 among people vaccinated due to the replacement of the Delta variant by the Omicron variant.
Therefore, the decrease in the protection of the different vaccines and the number of doses received must be urgently estimated. Although previous studies have quantified the effectiveness of the vaccine (EV) against symptomatic SARS-CoV-2 infection, estimates have been arbitrary.
Study: Decreased immunity induced by the SARS-CoV-2 vaccine: a systematic review and analysis of secondary data. Image credit: BaLL LunLa / Shutterstock
A new study published in the prepress server medRxiv * aimed to estimate the decrease in vaccine protection by conducting a systematic review of the study literature that reported VE at different times after vaccination.
About the study
The study included the selection of abstracts and titles of peer-reviewed preprints and journals in English for the identification of VE manuscripts against SARS-CoV-2 infection (including symptomatic and asymptomatic infection), as well as a symptomatic disease until June 21, 2022., the full texts of the manuscripts were examined according to the eligibility criteria of the current study which included the estimation of EVS after the primary vaccination dose (which includes the two first doses), as well as a booster dose, comparison of the risk of infection between vaccinated and unvaccinated. individuals, VE estimation for two defined time intervals, information on circulating variants during VE evaluation, and VE estimation for all age groups that are eligible for vaccination.
Studies measuring VE during the first 14 days of vaccine administration and those comprising less than 20 infections in a vaccinated group were excluded from the analysis.
Study results
The results indicated that of the 39 articles that reported evidence of VE only ten articles matched the eligibility criteria and provided an estimate of VE for the mRNA-1273, BNT162b2, and ChAdOx1 nCoV-19 vaccines against Alpha, Omicron variants. the Delta. It was observed that VE 14 days after the second dose of mRNA-1273 and BNT162b2 was 94.7% and 92.45%, respectively, compared to the Delta variant (symptomatic and asymptomatic). Although a similar VE was observed for ChAdOx1 nCoV-19 in Quebec, the VE was found to be lower compared to the other two vaccines after the second dose, as well as 3 months after vaccination in Colombia. British and the United Kingdom.
No difference in VE versus Delta was observed at 9 months after vaccination with nCoV-19 and mRNA-1273 ChAdOx1. However, a decrease in VE was observed in the case of BNT162b2 against both Delta and Omicron infections. It was observed that the EV against Omicron infection for three doses of BNT162b2 was 82.4%, 31.5%, and 19.0%, respectively, at 14 days, 6, and 9 months after administration. of the last dose of vaccine.
The results also reported that the VE 14 days after the administration of the second dose for BNT162b2, ChAdOx1 nCoV-19 and mRNA-1273 was 93.6%, 76.2% and 96.2%, respectively. against symptomatic Delta infections. The corresponding VE against symptomatic Omicron infection was observed to be 83.6%, 56.1%, and 76.3% for mRNA-1273, ChAdOx1 nCoV-19, and BNT162b2, respectively.
It was observed that VE decreased to 40.2%, 64.4% and 74.1% for ChAdOx1 nCoV-19, BNT162b2 and mRNA-1273, respectively, at the 6-month dose after the second against symptomatic Delta infections. It was observed that VE against symptomatic Omicron infection at 6 months after the second dose was 12.0%, 7.5%, and 8.3% for mRNA-1273, ChAdOx1 nCoV-19, and BNT162b2, respectively. . VE against symptomatic Omicron infection at 9 months post-vaccination was observed to be less than 5% for all vaccines. In addition, it was observed that the EV for the booster dose against symptomatic Omicron infection was between 11.7% and 22.2%.
Therefore, the current study showed that Omicron infection and symptomatic disease were associated with significant immune leakage after two doses of vaccination. However, booster doses could restore vaccine protection to levels similar to those observed shortly after the second dose. They could also reduce the rate of decline. However, the continued emergence of new underlines of Omicron or other possible future variants of SARS-CoV-2 requires further vaccination efforts to prevent the resurgence of patients with COVID-19.
Limitations
The study has certain limitations. First, the sample size of the study was quite small. Second, the duration of the monitoring period of the effectiveness of booster doses was limited. Third, preferential testing of symptomatic individuals may have caused a bias. Fourth, different study designs could have affected the original estimates of vaccine efficacy. Finally, recent studies indicate that hybrid and natural immunity are more durable compared to vaccine-induced immunity.
* Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guided by clinical practice or health-related behavior, or treated as established information.