Table A1.

Characteristics of SARS-CoV-2 variants of concern.

SARS-CoV-2 Variant	Alpha	Beta	Gamma	Delta	Omicron
Scientific Name	B.1.1.7	B.1.351	P.1	B.1.617.2	B.1.1.529
First reported (geographical location/date)	United Kingdom September 2020	South Africa May 2020	Brazil November 2020	India October 2020	Botswana, South Africa November 2021
Number of mutations/spike mutation of interest	23 mutations N501Y, D614G, P681H	21 mutations K417N, E484K, N501Y, D614G, A701V	17 mutations K417T, E484K, N501Y, D614G, H655Y	∼23 mutations L452R, T478K, D614G, P681R	∼50 mutations G339D, S371L S373P, S375F, K417N, N440K, G446S, S477N, T478K, E484A, Q493R, G496S, Q498R, N501Y, Y505H, D614G, T547K, H655Y, N679K, P681R
Transmissibility	∼50–70% [100,105,106] compared to the wild type ∼30–40% [100] Compared to other circulating lineages ∼43–90% [104,108] compared to proceeding variants.	∼23–50% [157,158,159] compared to ancestral lineages	1.4–2.2 [193,197] times compared to the wild type and 46% [197] compared to previous variants.	1.4–2.0 [229,237] compared to other lineages. 60–70% [232,233] more transmissible than B.1.1.7.	2.7–3.7 [306,307] times compared to the Delta variant.
Infectivity	0.1% in early October to 49.7% in late November 2020 [63]. 3.7-fold rise in December 2020 [109].	Reinfection cases were reported [163].	5.3% in the biweekly period of 11–24 April 2021 to 11.1% in the period of 23 May–5 June 2021 [202]. 0% in the period from November 2020 to 73% in January 2021 [203].	60% more infectious than the wild type [242]. 0.6% during April 2021 to 11.1% in May–June 2021, then surging to 83.2% in July 2021 [202].	13% to 73% in the period of 13–17 December 2021 [98]. >50% infections in mid-November 2021 [315]. 5.41-10-fold higher risk of reinfection than Delta [249,319]. Omicron is estimated to infect three to six times as many people as Delta over the same time [320].
Disease severity	1.5 to 1.7 [114,499] increased risk of hospitalization 62% higher risk of hospital admission compared to wild type [120]. 30% to 50% greater mortality rate [119,122] 1.64 mortality hazard ratio compared to preceding lineages [121].	2.16–3.6-fold higher risk of hospitalization and a 2.23–3.3-fold elevated risk of ICU admission [166,168]. 1.24-fold higher risk of progressing to severe disease than B.1.1.7 and 1.57-fold increased risk of mortality [170].	1.7–2.6-fold higher risk of hospitalization and a 2.06–2.2-fold higher risk of ICU admission [166,208,209].	2.26–2.83-fold higher risk of hospitalization compared to the B.1.1.7 variant [115,248,251]. 108–120% higher risk of hospitalization, a 235–287% higher risk of ICU admission, and a 133–137% higher risk of mortality [243,251].	50–70% less likely to be admitted to hospital than those infected with the Delta variant [323,360]. Two-thirds reduction in the risk of COVID-19 hospitalization when compared to Delta [321].
Viral load/Ct values	The median Ct values for the ORF gene target (22.30 vs. 18.16; p < 0.0001) and N-gene target (23.16 vs. 19.39; p < 0.0001) were considerably lower in SGTF samples compared to non-SGTF samples [129]. Virus loads in SGTF samples can be 104 times higher than those in non-SGTF samples [129]. Viral load was higher in B.1.1.7 samples than in non-B.1.1.7 samples, as determined by cycle threshold value (mean 28.8, SD 4.7 vs. 32.0, 4.8) [123].	Viral load at symptom onset was higher in B.1.351 variants than in historical variants, with a Ct value of −1.15 (−1.57, −0.697) lower than preceding strains [171].	Viral load was ten times (Ct = 19.8 vs. 23.0; p < 0.0001) higher than in non-Gamma patients [197]. Decrease in the median Ct values (25 to 22) from nasopharyngeal swab samples examined by RT-qPCR (p < 0.0001) between June 2020 and February 2021 [211].	Larger viral loads and a longer Ct ≤ 30 [246]. Much larger viral load than wild-type infections, with median Ct values for the N gene of the Delta variant of 23.0, which is significantly lower than the wild-type N gene’s values (median: 36.5) [9]. Viral levels up to 1260 times higher than those infected with the original strain [260].	Viral RNA content in the lungs was 3 log10 lower than in animals infected with D614G [338]. Mean peak Ct value for Omicron was 23.3 vs. 20.5 for Delta, underlining that the lower the Ct value, the higher the peak viral load [339]. Lower infectious virus loads than Delta-infected patients (5.2-fold, 0.715 log10) [341].
Estimated reproduction numbers (R0/Rt)	Rt = 1.25 during lockdown (UK) [132]. Rt increased 1.35 between September and December 2020, when compared to pre-existing variants (UK) [110]. R0 = 1–2 in November 2020 (UK) [104]. Rt = 1.4 in February 2021, then decreased to reach 1 in March, then 0.8 in April 2021 (Italy) [133]. R0 = 0.8–1.5 between January and March 2021 (Czech Republic) [134]. Rt > 2 between January and April 2021 (India) [136]. Rt = 1.44 between December 2020 and 3 February 2021 (Canada) [137]. Rt = 0.97 between August 2020 and January 2021, then increased > 1 from January 2021 to March 2021 [45], reaching 1.6 in January 2021 (Qatar) [45]. Rt varied from 1.1 to 2.8 (systematic review of ∼15 studies) [106].	Rt = 1.55 (95% CI: 1.43–1.69) (based on data from multiple countries. including England, Wales, Scotland, Denmark, USA, and South Africa) until 12 February 2021 [138].	Rt = 2.6 based on data collected before January 2021 (Brazil) [197]. Rt = 38% higher than non-VOCs, 10% higher than Alpha, and 17% higher than Beta (based on global data) until June 2021 [159].	R0 = 3.2–5.0 between May and June 2021 (China) [239,265]. R0 = 5.08–6.0 in July 2021 (China) [266]. R0 = 5.2 during May 2021 (UK) [267].	Rt = 0.8–2.5 in November 2021 (South Africa) [315,342]. Rt > 3 between November and December 2021 (UK) [319]. Rt was 4.2 times higher than the Delta variant (95% CI: 2.1, 9.1) during November 2021 (South Africa) [306]. R0 was equal to 1.90 (95% CI: 1.50–2.43) during November and December 2021 (South Korea) [343]. Rt = 3.19 (95% CI: 2.82–3.61) times more than that of Delta during December 2021 (Denmark) [344]. Rt = 2.5 during December 2021 (US) [345]. Rt = 1.8–3.1 in December 2021 (Italy) [346]. Rt = 1.34–3.57 depending on the location and vaccination rate, according to data obtained in many areas as of January 2022 (India) [377].
Vaccine Effectiveness Pfizer (BNT162b2) AstraZeneca (ChAdOx1) Moderna (mRNA-1273) Novavax (NVX-CoV2373) Johnson & Johnson (Ad26.COV2.S)	Estimated reduction in neutralization by less than 2-fold for both Pfizer and Moderna vaccines [145,146,148], by 5- to <10-folds for AstraZeneca and between 2 and <5-fold for Johnson & Johnson [147]. Novavax was 85.6% effective in reducing symptomatic COVID-19 infection (UK) [139,141]. Moderna was 88% effective 14 days after the first dose and 100% ≥ 14 days after the second dose [140]. Pfizer was 83% effective in the overall population and 93% in SARS-CoV-2-experienced subjects (100-day cumulative incidence: 5.78%) (Italy) [150].	Estimated reduction in neutralization by 5 to <10-fold for Pfizer, Moderna, and AstraZeneca vaccines and by more than 10-fold for Ad26.COV2.S [147]. Novavax revealed 89% efficacy (UK) and 60% efficacy (South Africa) [181,182]. Moderna and Pfizer exhibited 1.2-fold reduced nAb titers 3–4 weeks post-second dose (US) [183]. Moderna was 72% (US), 66% (Latin America), and 57% (South Africa) effective 28 days after immunization [181,182]. Moderna was 61% effective after the first dose and 96% after the second dose [140].	Estimated reduction in neutralization by 2 to <5-fold for Pfizer, Moderna, AstraZeneca, and Johnson & Johnson vaccines [147]. The median pseudovirus neutralizing antibody titers generated by Ad26.COV2.S were 3.3-fold lower against the P.1 variant [185]. Neutralizing ability of plasma from people who had previously been infected was 8.6 times lower against the P.1 isolates [218]. AstraZeneca vaccination was 77.9% effective against infection, 87.6% effective against hospitalization, and 93.6% effective against death following the two-dose regimen (Brazil) [214].	Estimated reduction in neutralization by 5 to <10-fold for Pfizer, by 2 to <5-folds for Moderna and AstraZeneca vaccines, and by less than 2-fold for Johnson & Johnson [149]. Delta was found to be more resistant to neutralization of convalescent serum (by a factor of 2) and vaccine serum (by a factor of 2.5–3.33) than the wild-type virus in his investigation [277]. In 95% of people, two doses produced a neutralizing response, with titers against Delta being 3-to-5 times lower than those against Alpha [276]. Both the Pfizer and AstraZeneca vaccines reduced the neutralizing titer for B.1.351 by eight to ninefold [178]. Pfizer and AstraZeneca vaccine have similar efficacies against the Delta variant, with 30.7% following a single dose (UK) [269]. Two AstraZeneca doses were less effective (67%) against Delta variant infection (UK) [269]. Pfizer was 45.3% effective ≥14 days after the first vaccine dose and 51.9% effective ≥14 days after the second dose (Qatar) [270]. Pfizer provided 95% protection against infection in people aged 16 and older following the two-dose regimen (data obtained from US, Argentina, Brazil, South Africa, Germany, and Turkey) [271]. Moderna was 73.7% and 73.1% effective ≥14 days after the first and second doses, respectively (Qatar) [270]. Moderna was found to be 94.1-96.8% effective in avoiding COVID-19 sickness, including severe disease (US) [273]. Gam-COVID-Vac (Sputnik V) was 91.6% effective (Moscow, Russia) [274].	Estimated 20- to 40-fold reduction in neutralizing activity with two doses of Pfizer vaccine [362] and by more than 10-fold for both AstraZeneca and Moderna vaccines [361,362]. 22.9-fold higher neutralization resistance than the ancestral D614G 3–4 weeks after receiving a second dose of either mRNA-1273 or BNT162b2 (US) [183]. Three to eightfold reduction in neutralization titers for Omicron compared to Delta in a study conducted in South Africa [359]. Pfizer was 70% effective during the proxy Omicron period (South Africa) [356]. Pfizer and Moderna booster effectiveness was ∼50% (Qatar) [304]. Reduced vaccine effectiveness against infection to 33%, down from 80% against Delta (South Africa) [295]. Pfizer and Moderna third/booster vaccine doses were associated with a 57% reduction in the risk of symptomatic infection when compared to 25 weeks after the second dose [321]. Booster doses (3X) were found to provide a high level or protection, exceeding 80% under certain circumstances [317]. Omicron may be twice as likely to evade existing vaccinations compared to Delta [299].