Table 2. Vaccine Efficacy against Mild-to-Moderate Symptomatic Covid-19 Confirmed by Nucleic Acid Amplification Test.*.
| End Point | Baseline Serologic Status† | Total No. of Cases | Placebo | Incidence Risk | Vaccine | Incidence Risk | Vaccine Efficacy‡ |
|---|---|---|---|---|---|---|---|
| no./total no. (%) | per 1000 person-yr (person-days) | no./total no. (%) | per 1000 person-yr (person-days) | % (95% CI) | |||
| Mild-to-moderate illness with onset >14 days after second injection | Seronegative | 42 | 23/717 (3.2) | 93.6 (89,714) | 19/750 (2.5) | 73.1 (94,881) | 21.9 (−49.9 to 59.8) |
| Mild-to-moderate illness associated with B.1.351 variant with onset >14 days after second injection | Seronegative | 39 | 20/714 (2.8) | 81.6 (89,448) | 19/750 (2.5) | 73.1 (94,881) | 10.4 (−76.8 to 54.8) |
| Mild-to-moderate illness with onset >14 days after second injection, regardless of baseline serostatus | Any | 46 | 24/865 (2.8) | 81.9 (106,898) | 22/884 (2.5) | 73.2 (109,659) | 10.6 (−66.4 to 52.2) |
| Mild-to-moderate illness with onset >14 days after one dose until October 31, 2020, a proxy for non-B.1.351 variant infection | Overall | 15 | 12/938 (1.3) | 31.1 (140,774) | 3/944 (0.3) | 7.6 (143,140) | 75.4 (8.9 to 95.5) |
The prespecified primary end point was Covid-19 illness of any severity, which includes mild, moderate, and severe illness confirmed by nucleic acid amplification test. Because no participants in the trial had severe Covid-19, the term “mild to moderate” is used. Participants were asked to present for investigation of symptoms considered suggestive of Covid-19, including respiratory symptoms (new-onset cough; new-onset rapid breathing; new-onset shortness of breath, or breathlessness, or difficulty breathing; sore throat; loss of smell or smell disturbance; nasal congestion; or runny nose) and nonrespiratory symptoms (fever or feverishness, myalgia, chills, loss of taste, headache, diarrhea, fatigue or weakness, nausea or vomiting, or loss of appetite) (see Table S1). Details of the grading of Covid-19 severity with nucleic acid amplification testing are provided in Table S2. The case-severity distribution was as follows: mild, 32 (17 in placebo recipients and 15 in vaccine recipients), and moderate, 10 (6 in placebo recipients and 4 in vaccine recipients).
Serologic status was evaluated with the use of an assay to detect IgG to SARS-CoV-2 nucleoprotein in serum obtained on the day of the first injection.
Vaccine efficacy against end points included in the secondary objectives are reported. Confidence intervals have not been adjusted for multiple comparisons.