Vaccination, in general, is effective in protecting high-risk populations against severe COVID-19 infections and COVID-19-associated mortality. A summary of special population groups with regards to their features, prognosis of infection, and vaccination decision based on current evidence is listed in. Patients without contraindications should be prioritized for vaccination under the careful supervision of healthcare workers after balancing the benefits and risks of vaccinations.
COVID-19 has been spreading globally since late 2019 [1]. There is no definitive cure to date. The consequences of being infected with COVID-19 can be multi-faceted, such as multisystem inflammatory syndrome in children, acute multi-organ failure in adults, and long COVID-19 syndrome in all recoverees [2,3,4,5][2][3][4][5]. Global vaccination programs and multiple preventive measures are the most effective ways to curb rapid transmission. The progress of clinical trials has been accelerating globally to test the protective efficacy of different vaccines [6]. However, there remains a great hesitancy to receive the vaccines due to various reasons, such as fear of the side effects of the vaccination, especially in subjects with underlying co-morbidities [7]. The hesitancy rate of vaccination was found to be 19% in the United States [8], 35% in Ireland, and 31% in the United Kingdom [9]. The major factor is the uncertainty of the safety and efficacy of vaccination in high-risk groups. This review aims to review the most updated evidence concerning COVID-19 vaccination in high-risk groups to facilitate their decision-making.
Thus, geriatric populations should consider their risk factors, risk of COVID-19-associated mortality, type of vaccination, and vaccination risks and benefits before making a vaccination decision. Counseling on individual risk profile should be done by healthcare workers if in doubt.
Transplant recipients have a higher risk of severe COVID-19 infections [65,66][10][11]; they are recommended to receive vaccinations, unless there are other contraindications. Their family members should also consider vaccination to prevent cross-infection between family members.
More recently, the American Diabetic Association and Centre for Disease Control and prevention advocated prioritizing vaccination to diabetic patients in order to minimize their infection risks [114,115][12][13].
In view of the uncertainty of the impact of COVID-19 vaccinations in pregnant women, there have been opposing opinions as to whether pregnant women should receive the vaccination. The American College of Obstetricians and Gynecologists (ACOG), American Society for Reproductive Medicine (ARSM), and the Society for Maternal–Fetal Medicine (SMFM) advocate vaccination in all pregnant and lactating women [140[14][15][16],141,142], while the World Health Organization (WHO) advocates vaccinations only in high-risk pregnant women such as medical care workers or those with co-morbidities that add to the risk of severe diseases [143][17].
Several contraindications have been listed by guidelines and pharmaceutical companies. Absolute contraindications are listed in Table 1 . The United States Centre for Disease Control and Prevention recommends absolute contraindications in two scenarios [144][18]: History of a severe allergic reaction (e.g., anaphylaxis) after a previous dose or to a component of the COVID-19 vaccine. Immediate allergic reaction of any severity to a previous dose or known (diagnosed) allergy to a component of the COVID-19 vaccine.
Table 1.
Absolute contraindications of vaccinations.
Absolute Contraindications |
Type of Vaccine | Recommended Actions |
---|
Severe allergic reaction, e.g., anaphylaxis | All [144] | All [18] | 1. Do not vaccinate 2. Referral to allergy immunologist 3. Consider other vaccine alternatives |
Immediate allergic reaction | All [144] | All [18] | 1. Risk assessment 2. Referral to allergy immunologist 3. Prolong observation period after vaccination (e.g., 30 min) |
The components of the COVID-19 vaccine are listed in Table 2.
Table 2. Components of 24 COVID-19 vaccines with emergency use authorizations by national regulatory authorities (as at 13 September 2021). The first 7 vaccines on the table have been approved for emergency or full use by at least one WHO-recognized stringent regulatory authority (Pfizer, Moderna, Janssen, Sinovac, Oxford–AstraZeneca, Serum Institute of India Covishield, Sinopharm-BBIBP). The remaining vaccine candidates were arranged in alphabetical order.
Type of Vaccine | Active Ingredient | Inactive Ingredients | |||
---|---|---|---|---|---|
Pfizer (mRNA) [145] The United States | Pfizer (mRNA) [19] The United States |
Nucleoside-modified mRNA encoding the viral spike (S) glycoprotein of SARS-CoV-2 |
| ||
Moderna (mRNA) [146] The United States | Moderna (mRNA) [20] The United States |
Nucleoside-modified mRNA encoding the viral spike (S) glycoprotein of SARS-CoV-2 |
| ||
Janssen (viral vector) [147] The United States | Janssen (viral vector) [21] The United States |
Recombinant, replication-incompetent Ad26 vector encoding a stabilized variant of the SARS-CoV-2 spike (S) protein |
| ||
Sinovac/Coronavac (Vero cell) [148] China | Sinovac/Coronavac (Vero cell) [22] China |
Inactivated SARS-CoV-2 virus (CZ02 strain) |
| ||
Oxford–AstraZeneca Vaxzevria [149] The United Kingdom | Oxford–AstraZeneca Vaxzevria [23] The United Kingdom |
Chimpanzee adenovirus encoding the SARS-CoV-2 Spike (S) protein ChAdOx1-S |
| ||
Serum Institute of India Covishield (Oxford–AstraZeneca formulation) [46,150] India | Serum Institute of India Covishield (Oxford–AstraZeneca formulation) [24][25] India |
Recombinant, replication-deficient chimpanzee adenovirus vector encoding the SARS-CoV-2 Spike (S) protein in genetically modified human embryonic kidney 293 cells |
| ||
Sinopharm-BBIBP (inactivated virus in Vero cells) [151] China | Sinopharm-BBIBP (inactivated virus in Vero cells) [26] China |
Inactivated SARS-CoV-2 virus (HB02 strain) in Vero cell culture |
| ||
Sputnik V (viral vector) [152] Russia | Sputnik V (viral vector) [27] Russia |
Modified replication-deficient Ad26 and Ad5 encoding the SARS-CoV-2 spike(S) protein |
| ||
Abdala [153,154,155] Cuba | Abdala [28][29][30] Cuba |
Protein subunit vaccine containing COVID-19-derived proteins | No clinical results and information on ingredients found on electronic databases (PubMed, Google Scholar, Medline, Scopus, Embase) | ||
Chinese Academy of Medical Sciences Covidful [156, | Covidful [31] | 157] China | Chinese Academy of Medical Sciences[32] China |
Inactivated virus vaccine | No clinical results and information on ingredients found on electronic databases (PubMed, Google Scholar, Medline, Scopus, Embase) |
Cansino Convidecia [158,159] China | Cansino Convidecia [33][34] China |
Recombinant replication-deficient adenovirustype 5-vectored vaccine expressing full-length spike gene based on Wuhan-Hu-1 (Genebank accession number YP_009724390) | Details of inactive components were not listed | ||
Covaxin [160,161], India | Covaxin [35][36], India |
Whole-virion inactivated SARS-CoV-2 antigen (strain: NIV-2020770) |
| ||
COVIran Barakat [162,163] Iran | COVIran Barakat [37][38] Iran |
Inactivated SARS-CoV-2 virus with Vero cell culture |
| ||
CoviVac [164,165] Russia | CoviVac [39][40] Russia |
Inactivated SARS-CoV-2 virus (strain:AYDAR-1) with Vero cell culture |
| ||
EpiVacCorona [166,167] Russia | EpiVacCorona [41][42] Russia |
Chemically synthesized peptides (short fragments of viral spike protein) conjugating to a carrier protein containing nucleocapsid proteins and maltose-binding proteins |
| ||
FAKHRAVAC [168,169] Iran | FAKHRAVAC [43][44] Iran |
Inactivated SARS-CoV-2 virus based with cell culture | Details of ingredients not published | ||
Medigen [170,171,172] Taiwan | Medigen [45][46][47] Taiwan |
Recombinant S-2P spike protein adjuvanted with CpG 1018 |
| ||
Minhai [173,174,175] China | Minhai [48][49][50] China |
Inactivated SARS-CoV-2 virus based with Vero cell culture | Details of ingredients not published | ||
QazCovid-in [176,177] Kazakhstan | QazCovid-in [51][52] Kazakhstan |
Inactivated SARS-CoV-2 virus based with cell culture | Details of ingredients not published | ||
Sinopharm-WIBP [178,179,180] China | Sinopharm-WIBP [53][54][55] China |
Inactivated SARS-CoV-2 virus (strain WIV-04) in Vero cell culture |
| ||
Soberana [181,182,183] Cuba | Soberana [56][57][58] Cuba |
Receptor binding domain of SARS-CoV-2 spike protein conjugated chemically to tetanus toxoid | Details of ingredients not published | ||
Sputnik light [184,185] Russia | Sputnik light [59][60] Russia |
Recombinant replication-deficient Ad26 encoding the SARS-CoV-2 spike(S) protein |
| ||
Zifivax [186,187] China | Zifivax [61][62] China |
Recombinant tandem repeat dimeric receptor-binding domain-based protein subunit vaccine |
| Details of ingredients not published | |
ZyCoV-D [188,India | ZyCoV-D [63] | 189] (DNA plasmid vactor) | [64] (DNA plasmid vactor) India |
DNA plasmid vector carrying the gene encoding the spike protein (S) of the SARS-CoV-2 virus | Details of ingredients not published |
Patients with absolute contraindications should reassess their risk of vaccination and refer to an allergy immunologist. A longer observation period (e.g., 30 min) after vaccination is recommended if they have an immediate allergic reaction or minor contraindications [144][18]. They may also choose to receive alternative COVID-19 vaccination from other brands without their allergic components. Currently, 24 COVID-19 vaccines have been granted emergency use authorizations by national regulatory authorities (as at 13 September 2021). The first seven vaccines listed in Table 2 have been approved for emergency or full use by at least one WHO-recognized stringent regulatory authority (Pfizer, Moderna, Janssen, Sinovac, Oxford–AstraZeneca, Serum Institute of India Covishield, Sinopharm-BBIBP).