Table 2. Secondary attack rate of SARS-CoV-2 by vaccination status of the index case (≥ 18 years) and vaccine effectiveness against transmissiona, crude and adjusted for age group of the index caseb and contactc and for vaccination statusd of contacts and month of notification date of the index case, the Netherlands, 1 February−27 May 2021 (n = 113,582 index cases, n = 253,168 contacts).
| Analysis | Unvaccinated index - SAR | Partly vaccinated index - SAR | Partly vaccinated index - crude VET (95% CI) | Partly vaccinated index - adjusted VET (95% CI) | Fully vaccinated index - SAR | Fully vaccinated index - crude VET (95% CI) | Fully vaccinated index - adjusted VET (95% CI) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Positive | Total | % | Positive | Total | % | Positive | Total | % | |||||
| Household contacts | 43,069 | 139,802 | 31 | 587 | 2,032 | 29 | 9 (−1 to 17) | 21 (12 to 28) | 79 | 706 | 11 | 72 (65 to 78) | 71 (63 to 77) |
| Household contacts - unvaccinated only | 42,382 | 135,974 | 31 | 432 | 1,517 | 28 | 12 (1 to 21) | 23 (14 to 32) | 68 | 604 | 11 | 73 (64 to 79) | 73 (65 to 79) |
| Other close contacts | 11,395 | 108,041 | 11 | 193 | 2,004 | 10 | 11 (−4 to 23) | 22 (9 to 33) | 50 | 583 | 9 | 22 (−5 to 42) | 22 (−5 to 43) |
| Other close contacts - unvaccinated only | 11,115 | 103,123 | 11 | 171 | 1,680 | 10 | 7 (−9 to 21) | 22 (8 to 34) | 44 | 462 | 10 | 14 (−18 to 37) | 24 (−5 to 45) |
| Household contacts - Vaxzevria | 43,069 | 139,802 | 31 | 364 | 1,306 | 28 | 13 (1 to 23) | 15 (4 to 26) | 5 | 39 | NP | 67 (16 to 87) | 58 (−12 to 84) |
| Household contacts - Comirnaty | 43,069 | 139,802 | 31 | 211 | 663 | 32 | −4 (−22 to 12) | 26 (12 to 37) | 70 | 596 | 12 | 71 (62 to 77) | 70 (61 to 77) |
| Household contacts - Spikevax | 43,069 | 139,802 | 31 | 12 | 63 | NP | 46 (−3 to 71) | 51 (8 to 74) | 2 | 40 | NP | 88 (51 to 97) | 88 (50 to 97) |
| Household contacts - Janssen | 43,069 | 139,802 | 31 | NA |
NA | NA | 2 | 31 | NP | 85 (37 to 96) | 77 (6 to 94) | ||
CI: confidence interval; GEE: generalised estimating equations; NA: not applicable; NP: not presented; SAR: secondary attack rate; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; VET: vaccine effectiveness against transmission.
a VET estimated by GEE with exchangeable correlation structure.
b Age groups index cases: 18–29, 30–49, 50–74, ≥75 years.
c Age groups contacts: 0–17, 18–59, ≥60 years.
d Vaccination status of contacts: unvaccinated, partly or fully vaccinated.
Partly vaccinated was defined as having received the first dose of a two-dose schedule at least 14 days before onset of symptoms. Fully vaccinated was defined as having completed a two-dose schedule at least 7 days or the one-dose Janssen schedule at least 14 days before symptom onset. Only percentages based on denominators above 100 are presented, please note the VET estimates based on smaller numbers are less precise.