Results
Between Sept 7 and Nov 24, 2020, 21 977 adults were eligible and randomly assigned to receive placebo (n=5476) or vaccine (n=16 501; figure 1).
The first database lock was on Nov 18, 2020, when 20 cases of COVID-19 had been reported. The interim safety analysis (analysis of rare adverse events) was done with data up to the first database lock. Since there was an increase in COVID-19 incidence in Moscow during November, the second database lock was done on Nov 24, 2020, when 78 COVID-19 cases had been reported. Data for the interim efficacy analysis and serious adverse events analysis are presented up to the second database lock.
74 participants from the vaccine group and 41 from the placebo group were excluded from analyses (figure 1). This preliminary analysis included 16 427 participants in the vaccine group and 5435 in the placebo group, who received at least one dose and continued participation in the trial. 14 964 in the vaccine group and 4902 in the placebo group had received two doses at the time of database lock (Nov 24, 2020) and were included in the primary outcome analysis (table 1). Median time from participants receiving the first dose to the date of database lock was 48 days (IQR 39–58). Among the participants who received two doses, the mean age was 45·3 years (SD 12·0) in the vaccine group and 45·3 years (SD 11·9) in the placebo group; the distribution by sex (p=0·619), incidence of concomitant diseases (p=0·420), and infection risk (p=0·851) were similar between the two groups (table 1).
Table 1
Baseline characteristics of participants who received two doses of assigned treatment and were included in primary outcome analysis
Vaccine (n=14 964) Placebo (n=4902)
Sex
Female 5821 (38·9%) 1887 (38·5%)
Male 9143 (61·1%) 3015 (61·5%)
Race
White 14 741 (98·5%) 4830 (98·5%)
Asian 217 (1·5%) 69 (1·4%)
Other* 6 (<0·1%) 3 (<0·1%)
Age group, years
18–30 1596 (10·7%) 521 (10·6%)
31–40 3848 (25·7%) 1259 (25·7%)
41–50 4399 (29·4%) 1443 (29·4%)
51–60 3510 (23·5%) 1146 (23·4%)
>60 1611 (10·8%) 533 (10·9%)
Age, years 45·3 (12·0) 45·3 (11·9)
Bodyweight, kg 81·3 (17·5) 81·6 (17·7)
Height, cm 173·1 (9·1) 173·3 (9·0)
Body-mass index, kg/m2 26·75 (4·56) 26·75 (4·55)
Concomitant diseases (diabetes, hypertension, ischaemic heart disease, obesity)† 3687/14 944 (24·7%) 1235/4892 (25·2%)
Risk of infection in volunteers† ‡
High 65/14 567 (0·4%) 23/4778 (0·5%)
Medium 3853/14 567 (26·5%) 1280/4778 (26·8%)
General 10649/14 567 (73·1%) 3475/4778 (72·7%)
Data are n (%) and mean (SD).
* Includes Black or African American, Native Hawaiian or other Pacific Islander, or undefined.
† Denominator shows number of participants for whom these data were available.
‡ High risk denotes those whose work involves interaction with patients with a confirmed diagnosis of COVID-19; medium risk is those who have professional contact with a large number of people, such as general practitioners, social workers, and shop assistants; and general risk denotes those with no additional risks associated with their professional activities.
From 21 days after the first dose of vaccine (the day of dose 2), 16 COVID-19 cases were confirmed in the vaccine group (of 14 964 participants; 0·1%) and 62 cases were confirmed in the placebo group (of 4902 participants; 1·3%); vaccine efficacy was 91·6% (95% CI 85·6–95·2; table 2). The observed vaccine efficacy was greater than 87% in all age and sex subgroups. Notably, vaccine efficacy was 91·8% (67·1–98·3) in participants older than 60 years. There were no cases (vaccine group) and 20 cases (placebo group) of moderate or severe COVID-19 confirmed at least 21 days after dose 1; thus, vaccine efficacy against moderate or severe COVID-19 was 100% (94·4–100·0). From 15 to 21 days after the first dose, efficacy was 73·6% (p=0·048), then from day 21, efficacy was 100% (p<0·0001; appendix p 11).
Table 2
Interim results on vaccine efficacy
Total cases Vaccine group Placebo group Vaccine efficacy (95% CI) p value
First COVID-19 occurrence from 21 days after dose 1 (day of dose 2)*
Overall 78 16/14 964 (0·1%) 62/4902 (1·3%) 91·6% (85·6–95·2) <0·0001
Age group (years)
18–30 5 1/1596 (0·1%) 4/521 (0·8%) 91·9% (51·2–99·3) 0·0146
31–40 17 4/3848 (0·1%) 13/1259 (1·0%) 90·0% (71·1–96·5) <0·0001
41–50 19 4/4399 (0·1%) 15/1443 (1·0%) 91·3% (73·7–96·9) <0·0001
51–60 27 5/3510 (0·1%) 22/1146 (1·9%) 92·7% (81·1–97·0) <0·0001
>60 10 2/1611 (0·1%) 8/533 (1·5%) 91·8% (67·1–98·3) 0·0004
Sex
Female 32 9/5821 (0·2%) 23/1887 (1·2%) 87·5% (73·4–94·2) <0·0001
Male 46 7/9143 (0·1%) 39/3015 (1·3%) 94·2% (87·2–97·4) <0·0001
Moderate or severe cases 20 0/14 964 20/4902 (0·4%) 100% (94·4–100·0) <0·0001
First COVID-19 occurrence after dose 1†
Any time after dose 1 175 79/16 427 (0·5%) 96/5435 (1·8%) 73·1% (63·7–80·1) <0·0001
From 14 days after dose 1 109 30/14 999 (0·2%) 79/4950 (1·6%) 87·6% (81·1–91·8) <0·0001
First COVID-19 occurrence after dose 2 (28 days after dose 1)*
All 60 13/14 094 (0·1%) 47/4601 (1·0%) 91·1% (83·8–95·1) <0·0001
Data are n/N (%), unless otherwise stated.
* Includes those who received both doses.
† Includes participants who received at least one dose.