What is the efficacy of the new COVID-19 (Coronavirus Disease 2019) vaccines, such as Pfizer-BioNTech (BNT162b2) and Moderna (mRNA-1273), in preventing severe illness?

Efficacy of COVID-19 Vaccines in Preventing Severe Disease

The 2024-2025 COVID-19 vaccines are highly effective at preventing severe COVID-19 illness, hospitalization, and death, with vaccine effectiveness against hospitalization ranging from 49% (95% CI = 43%-55%) within 7-59 days after vaccination to 32% (95% CI = 0%-53%) for critical illness after 120-179 days. 1

Vaccine Efficacy by Type and Population

General Population

• mRNA vaccines (Pfizer-BioNTech and Moderna) demonstrate the highest efficacy:
  • 87% effectiveness against severe outcomes ≥84 days after first dose
  • 98% effectiveness against severe outcomes ≥112 days after second dose 2
  • Protection against symptomatic infection: 60% after one dose, increasing to 91% after two doses 3

Cancer Patients

• COVID-19 vaccination significantly reduces the risk of severe illness in cancer patients:
  • Vaccinated cancer patients are 56% less likely to experience hospitalization or death (odds ratio 0.44,95% CI 0.28-0.72) 1
  • Efficacy rates of 83% in patients with solid tumors and 72% in hematological malignancies 4

Pregnant Women

• COVID-19 vaccines provide crucial protection for pregnant women who are at higher risk:
  • Symptomatic pregnant women have 2-3 fold higher rates of ICU admission, invasive ventilation, and mortality compared to non-pregnant women 1
  • Risk is particularly elevated for pregnant women over 35 years, those with comorbidities, and those of Black, Asian, or Hispanic ethnicity 1

Duration of Protection and Waning Immunity

• Protection against severe disease is more durable than protection against infection:

  • VE against COVID-19–associated hospitalization: 49% (95% CI = 43%-55%) at 7-59 days post-vaccination
  • Declining to 14% (95% CI = 0%-27%) at 120-179 days 1
  • VE against critical illness remains more durable: 69% at 7-59 days and 32% at 120-179 days 1

• This waning protection necessitates booster doses, particularly for high-risk populations 1

Variant-Specific Protection

• The 2024-2025 COVID-19 vaccines target currently circulating SARS-CoV-2 strains (JN.1 and KP.2) 1
• Previous data showed VE against symptomatic infection was:
  • 58% (95% CI = 33%-73%) for XBB-sublineage infection
  • 37% (95% CI = 13%-51%) for JN.1-sublineage infection 1
• Two doses provide excellent protection against Alpha, Gamma, and Delta variants 2

Safety Profile

• The vast majority of adverse events are mild to moderate (grade 1 or 2):

  • Most common: injection site pain, fatigue, myalgia, headache, and fever 1
  • Rare serious adverse events include myocarditis/pericarditis (1-4 cases per 100,000) 4

• Benefit-risk assessment strongly favors vaccination:

  • For every 1 million males aged 12-29 years receiving a second dose:
    • Risk: 39-47 cases of myocarditis
    • Benefit: Prevention of 560 hospitalizations, 138 ICU admissions, and 6 deaths 1

Special Considerations

• Immunocompromised patients: May have reduced vaccine response but still benefit significantly from vaccination 1, 4

  • Additional doses recommended after a 2-month interval for patients receiving therapies known to weaken vaccine responses 1

• Pregnancy: COVID-19 vaccines are recommended due to the significantly higher risk of severe outcomes in pregnant women 1

• Cancer patients: Vaccination is strongly recommended even during treatment, with optimal timing 2-4 weeks prior to initiating cancer treatment when feasible 4

Clinical Implications

• COVID-19 vaccines remain a critical tool for preventing severe disease and death, particularly in high-risk populations
• The benefit-risk ratio strongly favors vaccination across all age groups and populations
• Booster doses are important for maintaining protection, especially for those at higher risk of severe outcomes
• Healthcare providers should emphasize the strong protection against hospitalization and death when discussing vaccination with patients

While no vaccine provides 100% protection, the COVID-19 vaccines have consistently demonstrated high effectiveness against the outcomes that matter most: severe disease, hospitalization, and death.