Thread by @vipintukur

How long population immunity induced by natural infection, primary-series vaccination, and booster vaccination against SARS-CoV-2 lasts?

A new study from Qatar offers some clues. 1/

Using a test-negative study design,
population immunity against infection of each of previous infection, primary-series vaccination, and booster vaccination were characterized at the national level month by month for 2 calendar years 2/

The 3 forms of population immunity showed rapid variation over time driven by waning of protection. Vaccine-derived population immunity declined by 1 absolute percentage point every 5 days! 3/

Omicron introduction immensely reduced the three forms of population immunity within one month by about 50 absolute percentage points. 4/

Previous-infection effectiveness against reinfection was strong before Omicron, but declined with time after a wave & rebounded after a new wave. Effectiveness dropped immediately after Omicron emergence from 88.3% in November 2021 to 51.0% in December 2021. 5/

Primary-series VE against infection was 84.0% in April 21, soon after introduction, before waning gradually to 52.7% by Nov’ 21.

VE declined linearly by ~1% point every 5 days. After Omicron, VE dropped suddenly from 52.7% in Nov 2021 to negligible levels in Dec 21. 6/

Booster effectiveness dropped immediately after Omicron emergence from 83.0% in November 2021 to 32.9% in December 2021, and continued to decline thereafter. 7/

Effectiveness of previous infection and vaccination against severe, critical, or fatal COVID-19 were generally >80% throughout the study duration. 8/

Takeaways:

1-Both previous-infection and vaccine population immunities vary rapidly at a national level creating fertile grounds for repeated waves of infection to occur even within months of each other. 9/

2-High levels of population immunity may not be sustained for more than a year or so.

3-So, preventing infection/reinfection, transmission, or future waves of infection cannot sustainably be done with current vaccines nor by the entire population being infected. 10/

4-Timely administration of boosters for those vulnerable to severe COVID-19 may remain essential for years to come.

5-Repeated waves of infection may also facilitate further evolution of the virus and continual immune evasion. 11/

6-Emergence of a new variant that is substantially different from circulating
variants can suddenly and immensely reduce population immunity leading to large epidemic wave. 12/

7-However, the durability of population immunity against severe COVID-19 will likely curtail the severity of future waves. 13/13

medrxiv.org/content/10.110…