Table 2 Trend tests for the incremental effect of the number of prior vaccinations on day 14 post-vaccination geometric mean titres (GMTs)

From: Antibody responses against influenza A decline with successive years of annual influenza vaccination

Year

Subtype

Substrate

Estimated post-vaccination GMT among vaccine-naïve HCW (95%CI)a

Estimated fold-change in GMT with each additional prior vaccination (95%CI)b

p-value

Z-test

p-value

Jonckheere-Terpstra

2020

A(H1N1)pdm09

cell

93 (77, 110)

0.83 (0.79, 0.87)

<0.001

<0.001

egg

200 (170, 240)

0.85 (0.81, 0.89)

<0.001

<0.001

A(H3N2)

cell

57 (50, 66)

0.93 (0.9, 0.97)

<0.001

<0.001

egg

420 (340, 510)

0.9 (0.86, 0.95)

<0.001

<0.001

2021

A(H1N1)pdm09

cell

140 (110, 170)

0.79 (0.76, 0.84)

<0.001

<0.001

egg

500 (400, 640)

0.85 (0.8, 0.89)

<0.001

<0.001

A(H3N2)

cell

94 (77, 120)

0.87 (0.83, 0.91)

<0.001

<0.001

egg

290 (240, 350)

0.88 (0.84, 0.92)

<0.001

<0.001

  1. Estimates shown are from separate linear regression models of the d14 post-vaccination titre on the number of prior vaccinations, where number of prior vaccinations is assumed to have a linear relationship with the outcome (d14 post-vaccination titre) and is modelled as a continuous variable
  2. aThe estimated post-vaccination GMT is the intercept from the linear regression model and represents the GMT for the group with 0 prior vaccinations
  3. bThe estimated fold-change in GMT with each additional prior vaccination is the coefficient for the prior vaccination term from the linear regression model; e.g., for 2020 H1 the expected GMT for 2 prior vaccinations is 93 * 0.83 * 0.83 = 63). The p-value for the Z test indicates a linear trend of decreasing post-vaccination titre with increasing numbers of prior vaccinations. The Jonckheere-Terpstra test is an alternative test for linear trend. P-values assess statistical significance at the α = 0.05 level. 95%CI: 95% confidence interval; HCW: healthcare worker; GMT: geometric mean titre
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