The efficacy and effectiveness of the COVID-19 vaccines in reducing infection, severity, hospitalization, and mortality: a systematic review

Figures & data

Figure 1. A diagrammatic illustration summarizing the structure of the review.

Table 1. The highest effectiveness/efficacy values obtained for each category (infection, severity, mortality, and hospitalization) for each vaccine’s 1st dose (partial vaccination). The highest value recorded against a variant is also included. If the highest value was obtained in analysis toward a particular variant, only that value is included

Vaccine	Infection		Severity		Hospitalization		Mortality		Efficacy total no. of studies	Effectiveness total no. of studies
	Efficacy	Effectiveness	Efficacy	Effectiveness	Efficacy	Effectiveness	Efficacy	Effectiveness
Pfizer	NR	91 (90% CI 83–98) at ≥21 days after vaccination^[Citation43] B.1.1.7* 70 (CI 55–85) at ≥21 days after vaccination^[Citation41] B.1.351 16.9 (CI 10.4–23)^[Citation25]	NR	85 (CI 71–92) at 15–28 days after vaccination^[Citation26] B.1.1.7* 62 (CI 39–80)^[Citation34] B.1.351¶ 0 (CI 0–19)^[Citation25]	NR	85 (CI 71–92) at 15–28 days after vaccination^[Citation26] B.1.1.7* 74 (CI 56–86)^[Citation34]	NR	B.1.1.7* 72 (CI 19–100) at 14–20 days after vaccination^[Citation34] B.1.351¶ 0 (CI 0–19)^[Citation25]	0	15^[Citation25,Citation26,Citation30,Citation31,Citation33,Citation34,Citation38–41,Citation43,Citation50,Citation52,Citation54,Citation55,Citation60]
Moderna	95.2 (CI 91.2–97.4) at ≥14 days after vaccination^[Citation28]	51.7 (CI 37.3–63.0) at ≥7 days after vaccination^[Citation55]	NR	NR	NR	NR	NR	NR	1^[Citation27]	1 ^[Citation55]
AstraZeneca	63.9 (46.0–75.9) at 22–90 days after vaccination^[Citation65]	74% (HR 0.26 (CI 0.19–0.35) reduction in risk of testing positive. at ≥28 days after vaccination^[Citation38]	NR	NR	100 (97.5% CI one sided with lower limit:72 · 2) at ≥22 days after vaccination^[Citation65]	37% protection against hospitalization^[Citation30]**	NR	NR	2^[Citation49,Citation65]	2 ^[Citation30,Citation38]
J&J	-	-	-	-	-	-	-	-	-	-
Sputnik	91.6 (CI 85.6–95.2) at ≥21 days after vaccination^[Citation48]	NR	100 (CI 94.4–100.0) at ≥21 days after vaccination^[Citation48]	NR	NR	NR	NR	NR	1^[Citation48]	0
Novavax	-	-	-	-	-	-	-	-	-	-
Sinovac	NR	P.1 49.4 (CI 13.2–71.9)* at ≥14 days after vaccination^[Citation42]	NR	NR	NR	NR	NR	NR	0	1^[Citation42]
Pfizer/BioNTech (BNT162b2) Moderna (mRNA-1273)	NR	80 (CI 59–90) at ≥14 days after vaccination^[Citation63] 80 (CI 59–90)^[Citation36]	NR	NR	NR	NR	NR	NR	0	7^[Citation27,Citation32,Citation36,Citation52,Citation62–64]

*This was the dominant variant in the location of the study’s participants during the study period, suggesting that the indicated vaccine in the table is effective against this variant.

**This study concluded that the variant B.1.1.7 has a minor effect on the observed vaccine effectiveness.

*** Data was obtained from the USA study cohort, where the dominant variant was (Wuhan-Hu-1), the South Africa study cohort, where the dominant variant was (B.1.351) and from the Brazil study cohort, where the dominant variants were (P.2) and (Wuhan-Hu-1).

¶Includes fatal disease as well as severe or critical illness.

Table 2. The highest effectiveness/efficacy values obtained for each category (infection, severity, mortality, and hospitalization) for each vaccine’s 2nd dose (full vaccination). The highest value recorded against a variant is also included. If the highest value was obtained in analysis toward a particular variant, only that value is included

Vaccine	Infection		Severity		Hospitalization		Mortality		Efficacy total no. of studies	Effectiveness total no. of studies
	Efficacy	Effectiveness	Efficacy	Effectiveness	Efficacy	Effectiveness	Efficacy	Effectiveness
Pfizer	95.0 (CI 90.3–97.6) at ≥ 7 days after vaccination^Citation56	99.5 (CI 97.0–99.9) for symptomatic infections at ≥35 days after vaccination^Citation66 B.1.1.7** 94 (CI 87–98) for symptomatic infections. At >7 days after vaccination^Citation34 B.1.351: 75.0 (CI 70.5–78.9) at ≥14 days after vaccination^Citation25	NR	B.1.1.7: 100 (CI 81.7–100)* at 14 days after vaccination^Citation25 B.1.351: 100 (CI 73.7–100)* at 14 days after vaccination^Citation25	NR	B.1.1.7** 100 (CI 51.4–100)^Citation55	NR	B.1.1.7: 100 (CI 81.7–100)* at 14 days after vaccination^Citation25 B.1.351: 100 (CI 73.7–100)* at 14 days after vaccination^Citation25	1^[Citation56]	13 ^[Citation25,Citation27,Citation29,Citation31,Citation34,Citation39–41,Citation50,Citation52,Citation54,Citation55,Citation60,Citation66]
Moderna	94.1 (CI 89.3–96.8) at ≥14 days after vaccination^Citation28	93.3 (CI 85.7–97.4) at ≥7 days after vaccination^Citation55	100 (CI could not be estimated to 1.0)^Citation28	86.0 (CI 71.6–93.9) at ≥7 days after vaccination (severe infection requiring hospitalization)^Citation55	NR	100 (43.3–100) at ≥7 days after vaccination (ICU admission)^Citation55	NR	NR	1^Citation28	2 ^[Citation27,Citation55]
AstraZeneca	B.1.1.7 80.7% (CI 69.2–87.9) for all other strains. at ≥14 days after vaccination^Citation46	NR	NR	NR	NR	NR	NR	NR	4^Citation45,Citation46,Citation49,Citation65	0
Sputnik	-	-	-	-	-	-	-	-	-	-
Novavax	60.1 (CI 19.9–80.1) at ≥7 days after vaccination B.1.351*** 43.0 (CI – 9.8–70.4)^Citation61	NR	NR	NR	NR	NR	NR	NR	1^Citation61	0
J&J	NR	66.9 (CI 59.1–73.4) ¶ at ≥14 days after vaccination^Citation59	NR	83.5 (54.2 to 96.9) ¶ at ≥28 days after vaccination^Citation59	NR	100 (CI 74.3–100.0) ¶ at ≥28 days after vaccination^Citation59	NR		1^Citation59	0
Sinovac	NR	73.8 (CI 57.0–84.8) at ≥5 weeks after vaccination^Citation37	NR	NR	NR	NR	NR	NR	0	2^[Citation37,Citation42]
Pfizer/BioNTech (BNT162b2) Moderna (mRNA-1273)	NR	91.3 (CI 79.7–96.3) for symptomatic infection at ≥15 days after vaccination^Citation27	NR	96 (CI 95–99)^Citation64	NR	96 (CI 95–99)^Citation64	NR	98.7 (CI 91.0–99.8)^Citation64	0	6^[Citation27,Citation36,Citation52,Citation62–64]
J&J (Ad26.COV2.S) Pfizer/BioNTech (BNT162b2) Moderna (mRNA-1273)	NR	Number of new cases for those 65+ years of age was 82% lower, and 70% lower for those <65 years of age^Citation58	NR	NR	NR	Number of hospitalizations for those 65+ years of age was 80% lower, and 60% lower for those <65 years of age^Citation58	NR	Number of deaths for those 65+ years of age was 92% lower, and 87% lower for those <65 years of age^Citation58	0	1^[Citation58]

*Includes fatal disease as well as severe or critical illness.

**This was the dominant variant in the location of the study’s participants during the study period, suggesting that BNT162b2 is effective against this variant.

*** Variant was identified in 93% of sequenced samples.

¶ Data was obtained from the USA study cohort, where the dominant variant was (Wuhan-Hu-1), the South Africa study cohort, where the dominant variant was (B.1.351) and from the Brazil study cohort, where the dominant variants were (P.2) and (Wuhan-Hu-1).

Table 3. Data from 5 studies where vaccine effectiveness was assessed by different methods. . The different methods of assessment of vaccine effectiveness is shown for each study

Study	Type of study and country	Vaccine	Unvaccinated (N)	Vaccinated (N)	Method of assessment	Recorded difference post-vaccination	Notes
McEllistrem et al.^Citation51	Single-Center retrospective study USA	Pfizer-BioNtech	5	5	Nasopharyngeal viral load (NVL)	A single dose of vaccination was associated with 2.4 mean log10 lower NVL than detected in the absence of vaccination (p = .004)	Mean Log10 NVL in unvaccinated: 9.5 (9.3–9.8); vaccinated: 7.1 (5.4–8.8) The difference is statistically significant
Lillie et al.,^Citation47	Retrospective cohort study UK	Pfizer-BioNtech	NR	NR	RT-PCR tests	Significant negative correlation between cumulative vaccination and PCR positive cases (Pearsons R = −0.9061, p = .0019)	This study assessed the general effectiveness of the vaccine by looking at a large cohort of healthcare workers without dividing them into vaccinated and unvaccinated.
Jones et al.,^Citation44	Retrospective study UK	Pfizer-BioNtech	NR	NR	RT-PCR tests	26/3252 (0.8%, Wilson’s interval 0.6–1.2%) positive tests in unvaccinated health care workers (HCWs) (Ct < 36). 13/3535 (0.4%, Wilson’s interval 0.2–0.6%) positive tests in HCWs <12 days post-vaccination. 4/1989 (0.2%, Wilson’s interval 0.1–0.5%) positive tests in HCWs ≥12 days post-vaccination (p = .023 and p = .004)	Population numbers were not reported (only test numbers)
Daniel et al.,^Citation35	Observational study USA	Pfizer-BioNtech Moderna	8969 (6282 F, 2558 M, 129 unknown)	8121 fully vaccinated (5181 F, 2924 M, 16 unknown) 6144 partially vaccinated (3891 F, 2232 M, 21 unknown)	RT-PCR tests	Infections in: 234 of 8969 unvaccinated employees (2.61%; CI 2.29 to 2.96). 112 of 6144 partially vaccinated employees (1.82%; 95% CI 1.50 to 2.19). 4 of 8121 fully vaccinated employees (0.05%; CI 0.01 to 0.13) (P < .01 for all pairwise comparisons)	A greater than 90% decrease in the number of employees who were either in isolation or quarantine was observed. Real-world experience with SARS-CoV-2 vaccination at University of Texas Southwestern Medical Center (UTSW) has shown a marked reduction in employee’s incidence of infections
Mor et al.,^Citation53	Matched pairs analysis US	Pfizer-BioNtech Moderna	13221 (8091 F/5130 M	12,157 (7443 F/4714 M)	RT-PCR and antigen tests	1 week post vaccination: 2.5 fewer infections per 100 at-risk residents per week (CI 1.2–4.0). At 5  weeks, the predicted reduction in new infections was 5.2 cases per 100 at-risk residents (CI 3.2–7.3). By 5 to 8  weeks post-vaccine clinic, early vaccinated facilities had a predicted 1.1 to 3.8 fewer hospitalizations and/or deaths per 100 infected residents per day	Late vaccinated group was considered as the unvaccinatedgroup. CI

Figure 2. Screening and study selection protocol.

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