Do Covid-19 vaccine boosters continually reduce the likelihood of getting Covid-19?

COVID-19 Vaccine Boosters and Continued Protection Against COVID-19

COVID-19 vaccine boosters provide significant but time-limited additional protection against COVID-19 infection, with stronger and more durable protection against severe disease, hospitalization, and death compared to protection against infection alone. 1

Effectiveness of COVID-19 Boosters Against Infection

• During the Omicron-predominant period, monovalent mRNA primary series vaccine effectiveness against SARS-CoV-2 infection was substantially lower and waned over time since vaccination 1
• A third monovalent (booster) dose provided increased protection against infection during the Omicron predominance, but this protection also waned over time, especially during the BA.2/BA.2.12.1 and BA.4/BA.5 sublineage periods 1
• For adults, vaccine effectiveness against symptomatic COVID-19 with the delta variant peaked early after the second dose and then decreased by 20 weeks to 44.3% with the ChAdOx1-S vaccine and to 66.3% with the BNT162b2 vaccine 2
• In a UK study, by 6 months post-booster, the cumulative incidence of positive SARS-CoV-2 tests was actually higher in boosted than unboosted individuals, suggesting limited long-term protection against infection 3

Effectiveness Against Severe Disease and Death

• Booster doses provide substantially stronger and more durable protection against severe outcomes compared to protection against infection:
  • Against hospitalization: 80.0% effectiveness with ChAdOx1-S and 91.7% with BNT162b2 at 20+ weeks post-vaccination 2
  • Against death: 84.8% effectiveness with ChAdOx1-S and 91.9% with BNT162b2 at 20+ weeks post-vaccination 2
• In the UK, booster vaccination showed 97-99% absolute effectiveness against hospitalization or death in all age groups, with no evidence of waning up to 10 weeks 4
• For older adults (≥80 years), those receiving booster doses had 75% lower risk of SARS-CoV-2 infection, 82-83% lower risk of COVID-19 hospitalization and ICU admission, and 81% lower risk of death compared to those who completed primary vaccination ≥5 months earlier 5

Bivalent Boosters and Omicron Protection

• Bivalent boosters were developed specifically to address waning immunity and improve protection against newer Omicron variants 1, 6
• Bivalent boosters contain mRNA encoding spike proteins from both the original Wuhan-hu-1 strain and the Omicron BA.4/BA.5 sublineages 7
• In adults over 60 years, a fourth dose using bivalent mRNA vaccine provided significant additional protection compared to three doses of monovalent vaccine:
  • 52% reduction in COVID-19 infection risk
  • 61% reduction in hospitalization risk
  • 77% reduction in 30-day mortality risk 8

Waning of Protection Over Time

• Monovalent vaccine effectiveness against COVID-19–associated hospitalization during the BA.4/BA.5 period among immunocompetent adults aged ≥18 years was:
  • 49% at 14–149 days after dose 3
  • Declined to 34% at ≥150 days after dose 3 1
• For children aged 5–11 years, monovalent vaccine effectiveness against emergency department and urgent care visits was:
  • 51% at 14–59 days after dose 2
  • Declined to 18% at ≥150 days after dose 2 1
• For adolescents aged 12–17 years, vaccine effectiveness against emergency department and urgent care visits was 63% ≥7 days after dose 3 1

Special Considerations

• Waning of vaccine effectiveness was greater in persons 65 years of age or older than in those 40 to 64 years of age 2
• Greater waning in vaccine effectiveness against hospitalization was observed in:
  • Persons 65 years of age or older in clinically extremely vulnerable groups
  • Persons 40 to 64 years of age with underlying medical conditions 2
• Prior SARS-CoV-2 infection provides additional protection, with lower risk of COVID-19 infection, hospitalization, and death in both boosted and non-boosted individuals 8

Current Recommendations

• The Advisory Committee on Immunization Practices (ACIP) recommends that all persons aged ≥5 years receive a bivalent mRNA COVID-19 vaccine booster dose 1
• The bivalent booster should be administered at least 2 months after completion of any FDA-approved or FDA-authorized primary series or monovalent booster doses 1
• Persons who recently had a SARS-CoV-2 infection may consider delaying a booster dose by 3 months from symptom onset or positive test 6

In conclusion, while COVID-19 vaccine boosters do provide additional protection against infection, this protection wanes considerably over time. However, the protection against severe disease, hospitalization, and death remains more robust and durable, which is the primary goal of vaccination from a morbidity and mortality perspective.