There are currently three COVID-19 vaccines authorized under an Emergency Use Authorization in the US and across the US, everyone 16 years or older is currently eligible for vaccination with at least one of the vaccines, with expansion of eligibility down to age 12 likely soon. The vaccine coverage among eligible individuals remains uneven, but high coverage among adults has been achieved in some settings. While all currently authorized vaccines have high or very high effectiveness to prevent both SARS-CoV-2 infection and COVID-19 disease, some vaccinated individuals do become infected with SARS-CoV-2, resulting in what is referred to as a “breakthrough infection”. This document is a brief summary of published evidence related to COVID-19 vaccine effectiveness and breakthrough infections. Included are manuscripts published in peer-reviewed journals or on pre-print servers through May 12, 2021. References summarized in this report were drawn from the COVID-19 Literature Report (Lit Rep) team database. References that appeared in the daily Lit Rep are marked with an asterisk*, and the summary is shown in the annotated bibliography.
- All COVID-19 vaccines currently authorized for use under an Emergency Use Authorization in the US (Pfizer-BioNTech, Moderna, and Johnson & Johnson-Janssen) showed high vaccine efficacy (66% to 95%) to prevent COVID-19 disease in phase 3 efficacy trials.
- Real-world effectiveness of the currently authorized vaccines has matched the efficacy observed in the trial results.
- Effectiveness of the currently authorized vaccines has been similar across all age groups, but there is some indication that breakthrough infections are somewhat more common among older individuals and those who may be immunocompromised, including recipients of solid organ transplants.
- Vaccine effectiveness has been high among residents and staff in skilled nursing facilities, with some indication that nursing home residents who have recovered from a past SARS-CoV-2 infection tend to mount more robust immune responses following vaccination. Partial vaccination has shown >60% effectiveness among nursing home residents.
- Vaccinated individuals who subsequently become infected with SARS-CoV-2 are more likely to have asymptomatic or milder cases of COVID-19 and have lower viral loads compared to unvaccinated individuals who become infected. There is also direct and indirect evidence that vaccinated individuals who become infected are less likely to transmit the virus to others.
- All vaccines currently authorized for use in the US have shown effectiveness against the B.1.1.7 variant of SARS-CoV-1 that is comparable to earlier viral strains.
- Vaccine-induced immune responses show lower levels of neutralization against the B.1.351 and P.1 variants in laboratory tests, but the effectiveness of the currently authorized vaccines do not appear to be diminished to a substantial degree against B.1.351 or P.1, particularly for prevention of severe disease.
- Similarly lower neutralization has been observed against a number of the newer variants of concern, but there is no evidence at this time that the vaccine effectiveness is reduced against any of these variants. There is not yet enough evidence to draw strong conclusions about the effectiveness of vaccines against the newest emerging variants.