Several studies have shown the effectiveness of the BioNTech/Pfizer messenger ribonucleic acid (mRNA) BNT162b2 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine. Two doses of the vaccine have been shown to provide a short-term effect.
In a new study published in Nature Communications, a group of scientists from Israel sought to evaluate the long-term effectiveness of the BioNTech/Pfizer mRNA BNT162b2 vaccine. To this end, they assessed the correlation between time-from-vaccination and incidence of breakthrough infection within thespecified study period.
Duration of protection by vaccination
The Delta variant of SARS-CoV-2 was first identified in India; however, it is now to dominant circulating strain globally. Recently, several vaccinated individuals have reported SARS-CoV-2 infection, which has increased concerns about reduced vaccine efficacy against the Delta variant. Some studies report moderate differences in vaccine effectiveness and considerable antibody response against the Delta variant.
Taken together, it is important to evaluate the duration of protection provided by vaccines. This will help in effective resource allocation and vaccine administration. Furthermore, this information will also help in deciding the need for a third dose for longer protection.
A retrospective study
Israel had a rapid rollout of its mass vaccination campaign. The Maccabi Healthcare Services (MHS), which is Israel’s second-largest Health Maintenance Organization, has a centralized computerized database that covers 2.5 million members, which is about 26.5% of the population and provides a representative sample of the Israeli population. This data provided a window of opportunity to investigate the correlation between time-from-vaccination and vaccine effectiveness against the Delta variant.
The study population included all MHS members aged 16 and above who received the second dose of the Pfizer-BioNTech vaccine between January and April 2021. Individuals were considered fully vaccinated if they received two doses of the BNT162b2, with the second one administered within the 21-to-28-day interval set by national guidelines.
Individuals were excluded from the study if they had a positive SARS-CoV-2 polymerase chain reaction (PCR) assay test result before the start of the study period or disengaged from MHS for some reason between January and April. Dates of the first and second dose of the vaccine and results of any PCR tests for SARS-CoV-2 were included in the analysis.
Statistical models were employed to assess the correlation between time-from-vaccination and protection against breakthrough infection. In the analysis, the outcome was defined as a positive SARS-CoV-2 PCR test recorded between June 1, 2021 and July 27, 2021, which was the date of analysis.
Depending on the time-from-vaccination, the individuals were grouped into two separate groups including Early Vaccinees and Late Vaccinees. Early Vaccinees were individuals who received the second dose of the vaccine between January and February 2021, whereas Late Vaccinees were individuals who received the second dose between March and April 2021.