Waning of SARS-CoV-2 booster viral-load reduction effectiveness

Area of Science:

• Immunology
• Virology
• Epidemiology

Background:

• The BNT162b2 COVID-19 vaccine reduces viral load in breakthrough infections (BTIs), impacting infectiousness.
• Vaccine effectiveness in reducing viral load wanes over time post-vaccination and is temporarily restored by a booster.
• The duration of this restored effectiveness following a booster dose remains unclear.

Purpose of the Study:

• To evaluate the longevity of the viral-load reduction effectiveness of the BNT162b2 vaccine booster dose.
• To analyze the waning pattern of the booster's effect on reducing viral load in SARS-CoV-2 infections.

Main Methods:

• Analysis of SARS-CoV-2 qRT-PCR Ct values from over 22,000 infections during a Delta-variant-dominant period in Israel.
• Ct values of the RdRp gene were analyzed, adjusting for age, sex, and calendar date.
• Comparison of viral load reduction effectiveness between vaccinated individuals (post-booster) and unvaccinated individuals.

Main Results:

• Booster effectiveness in reducing viral load significantly declines within months post-administration.
• Initial viral load reduction (2.7 Ct increase) in the first month post-booster decays to insignificant levels by the third to fourth month.
• The rate of waning post-booster mirrors the waning observed after the second vaccine dose.

Conclusions:

• The effectiveness of the BNT162b2 vaccine booster in reducing viral load and potentially infectiousness wanes rapidly.
• This rapid waning suggests that the community-level impact on virus spread may be short-lived.
• Further research is needed to understand the implications for long-term vaccine strategies and public health interventions.