A team of scientists from Israel has recently claimed that antiviral immunity induced by the mRNA-based coronavirus disease 2019 (COVID-19) BNT162b2 gradually declines over time, highlighting the need for a third booster dose. The study is currently available on the medRxiv* preprint server.
Mass vaccination is one of the key interventions to bring an end to the COVID-19 pandemic. However, a potential barrier to vaccine-mediated COVID-19 management is the emergence of novel variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that are able to induce breakthrough infections in fully vaccinated individuals. In this context, some studies have shown that only a small proportion of BNT162b2-vaccinated individuals are susceptible to breakthrough infections by the beta or delta variants of SARS-CoV-2. In contrast, there is evidence claiming a high rate of breakthrough infection among vaccine recipients.
In Israel, mass vaccination programs were initiated in December 2020 with the Pfizer/BioNTech-developed BNT162b2 vaccine. Similar to most of the available vaccines, BNT162b2 contains prefusion-stabilized full-length spike protein as an immunogen. The two doses of the vaccine are administered intramuscularly at an interval of 21 days. By May 2021, Israel has experienced a 100-fold reduction in infection rates, with a small number of new infections detected mostly in unvaccinated individuals returning from abroad.
However, during June 2021, a rapid induction in new cases has been observed, with a significant proportion of new infections detecting in vaccinated individuals. The whole genome sequencing studies conducted during this period have revealed that almost 98% of new COVID-19 cases are caused by the delta variant.
In the current study, the scientists have investigated whether these vaccine breakthrough infections are caused by waning vaccine immunity.
The scientists searched the Ministry of Health database to collect information about Israeli residents who have received the BNT162b2 vaccine before June 2021. Specifically, they collected demographic details, vaccination status, and COVID-19-related outcomes of the residents. Since the delta variant became dominant in Israel during June 2021, they focused specifically on new infections detected between July 11 and 31, 2021. This represents the time period when the delta variant was predominantly circulating in the entire country.
The study was conducted on a total of 4,785,245 fully vaccinated individuals who did not have SARS-CoV-2 infection before the study period. Of all enrolled individuals, 12,927 tested positive for SARS-CoV-2, with 348 developing serious complications.
Among older adults aged 60 years or above, the infection rate was 3.2 cases per 1000 persons for those who received the vaccine in January 2021. In contrast, the infection rates were 2.1 and 1.6 per 1000 persons for those who received the vaccine in February and March, respectively. A similar trend was observed for people belonging to other age groups. These observations reveal a significant increase in infection rate as a function of time since the last vaccination.
Among people aged 60 years or above, the rates of severe COVID-19 were 0.29, 0.23, 0.15, and 0.10 per 1000 people for those who received the vaccine in January, February, March, and April – May, respectively. These findings indicate that, like the infection rate, the rate of severe disease increases significantly as a function of time since the last vaccination.
Regarding the level of protection, people aged 60 years or above who received the vaccine in March and April-May were 1.6-times and 2.1-times more protected against SARS-CoV-2 infection compared to their counterparts who received the vaccine in January. A similar trend of increasing protection with decreasing time since the last vaccination was observed in people from other age groups.
The study findings indicate that people fully vaccinated with BNT162b2 become susceptible to breakthrough infections 6 months after the last vaccine dose. Given the waning vaccine immunity, it might be necessary to immunize people, especially older adults, with a third vaccine dose for sustained protection against SARS-CoV-2 infection and severe COVID-19.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.