The risk of COVID-19 also varied by the number of COVID-19 vaccine doses previously received.

The higher the number of vaccines previously received,

the higher the risk of contracting COVID-19

Vaccine doses versus risk of covid during the 3-month study period

One dose, 1.7 times more likely to test positive for covid

Two doses, 2.63 times more likely to test positive for covid

Three doses, 3.1 times more likely to test positive for covid

More than three doses, 3.8 times more likely to test positive for covid

So compared to the unvaccinated

1, x 1.7

2, x 2.36

3, x 3.1

4, x 3.38

P = 0.001 means 999 out of 1,000 likely to be a genuine result

That 99.9% likely to be a genuine result

Effectiveness of the Coronavirus Disease 2019 (COVID-19) Bivalent Vaccine

In 2020

(published in 2021)

Evidence that vaccines prevented covid infection

This was when the human population had just encountered the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus

Things Have Changed (Dylan)

Bivalent antigens vaccines

Original vaccine and BA.4/BA.5 lineages of Omicron.

(Approved without demonstration of effectiveness in human clinical studies)

(Approved without demonstration of safety in human clinical studies)


To evaluate whether a bivalent COVID-19 vaccine protects against COVID-19.


Employees of Cleveland Clinic,
n = 51,011

Cumulative incidence of COVID-19 was examined over the following weeks.

Protection provided by recent and prior vaccination was evaluated

First bivalents given, 12 September 2022

Three-month study


Among 51,011 employees,

20,689 (41%) had had a previous documented episode of COVID-19,

42,064 (83%) had received at least two doses of a vaccine.

10,804 (21%) were bivalent vaccine boosted

COVID-19 occurred in 2,452 (5%) during the study.

(Pfizer 89%, Moderna 11%)

Risk of COVID-19 increased with time since the most recent prior COVID-19 episode

Risk of COVID-19 increased with the number of vaccine doses previously received.

Note, this is based on large numbers

Doses, 0 = 6,419 (12.6%)

Doses, 1 = 2,528 (5%)

Doses, 2 = 14,810 (45.9%)

Doses, 3 = 23,396 (45.9%)

Doses 4, 3,757 (7.4%)

Doses 5, 85 (<1%)

Doses 6, 16 (<1%)

The bivalent vaccinated state

Was independently associated with lower risk of COVID-19 (HR, 0.70)

(over the 3 months of the study)

Leading to an estimated vaccine effectiveness (VE) of 30%

CDCs latest variant data

Things Have Changed (Dylan)