The Pfizer-BioNTech COVID-19 vaccine remains one of the most studied vaccines in history, and its effectiveness depends on what you’re measuring and when. In pooled real-world studies, it prevented 94.3% of hospitalizations and 96.1% of deaths from COVID-19. Protection against infection is lower and fades faster, but the vaccine’s ability to keep people out of the hospital has held up well across multiple studies and years of data.
Protection Against Severe Disease and Death
The strongest case for the Pfizer vaccine has always been its performance against the worst outcomes. Across eight real-world studies pooled by the CDC, the vaccine was 94.3% effective at preventing hospitalization. Four studies looking specifically at deaths found 96.1% effectiveness. These numbers reflect the vaccine’s core value: even as its ability to block infection has shifted with new variants, it consistently reduces the chance that a COVID infection becomes life-threatening.
How Protection Fades Over Time
Vaccine protection doesn’t stay at its peak indefinitely. Research from UNC’s Gillings School of Global Public Health tracked how updated COVID boosters performed over time. At four weeks after vaccination, protection peaked at 52.2% against infection and 66.8% against hospitalization.
From there, the decline was steady. By 10 weeks, effectiveness against infection dropped to 32.6%, and by 20 weeks it was down to 20.4%. Protection against hospitalization held up better, sitting at 57.1% at 10 weeks. This pattern explains why health authorities have moved toward periodic updates rather than treating any single dose as permanent protection.
Performance Against Newer Variants
The virus that circulates today looks very different from the one the original vaccine targeted. The JN.1 variant, which descended from Omicron’s BA.2.86 lineage, carries 28 mutations shared with earlier strains plus 25 unique ones, including 10 in the part of the spike protein that antibodies latch onto. Lab studies show a substantial drop in the ability of vaccine-generated antibodies to neutralize JN.1 and its offshoots (KP.2, KP.3) compared to earlier variants like BA.2.
This is why vaccine formulations are updated regularly, much like the flu shot. Each new version is designed to better match the variants currently spreading, which restores some of the effectiveness lost to viral evolution.
Effectiveness in Children and Teens
A large CDC study spanning nine states tracked how the 2024-2025 updated vaccines performed in younger age groups. The results varied by age. Children aged 9 months through 4 years saw 76% effectiveness against COVID-related emergency department and urgent care visits within the first six months after vaccination. For kids aged 5 to 11, that number was 51%. Adolescents aged 12 to 17 did slightly better at 61%.
The stronger protection in the youngest children likely reflects that many were receiving their initial vaccine series rather than a single updated dose on top of prior immunity and infections.
Reducing Spread to Others
Beyond personal protection, the Pfizer vaccine also reduces the chance of passing the virus to household members. A population-level study published in The Lancet found that fully vaccinated people who caught the Delta variant were about 80% less likely to transmit it to others in their household compared to unvaccinated people. On the receiving end, vaccinated household contacts were roughly two-thirds less likely to get infected when exposed to an infected family member. These figures apply to the Delta period, and transmission reduction is expected to be lower against Omicron-lineage variants, but the vaccine still provides a meaningful buffer.
Protection Against Long COVID
One of the more compelling benefits is reduced risk of long COVID, the persistent symptoms that can linger for months after infection. During the Delta wave, the Pfizer vaccine was 95.4% effective at preventing long COVID in adolescents. That number dropped during Omicron, but remained significant: 60.2% effectiveness in children and 75.1% in adolescents.
In adults, the picture is more modest. A population-based study from Japan found that people with three or more vaccine doses had a 30% lower probability of developing long COVID symptoms overall, and a 39% lower probability of the neurological symptoms (brain fog, fatigue, concentration problems) that many long COVID patients find most disabling.
Current Vaccination Schedule
For the 2025-2026 season, the CDC recommends COVID-19 vaccination for everyone aged 6 months and older, though with an important change: the Pfizer vaccine is no longer authorized for children under 5. For that age group, only Moderna is available.
For ages 5 through 64, the recommendation is one dose of the updated vaccine, given at least eight weeks after any previous COVID dose. Adults 65 and older are recommended to receive two doses, spaced six months apart (with a minimum of two months between them). This extra dose for older adults reflects the faster rate at which immunity wanes in aging immune systems and the higher stakes of severe illness in that group.