How Well Do Rapid COVID-19 Tests Work? Antigen Tests Against PCR, 2022–2023

Summary

• Early in the pandemic, rapid antigen tests were found to detect potentially contagious infection but to be less sensitive than RT-PCR.
• In November 2022–May 2023, among infected people in a household study, antigen tests were 47% as sensitive as RT-PCR and 80% as sensitive as viral culture — still catching likely contagious infection, but missing many that PCR found.
• People at high risk of severe COVID-19 who could get antiviral treatment should seek a more sensitive test from a health care provider, and clinicians should consider RT-PCR for them.

Why test again

Antigen tests were authorized early and rolled out widely when immunity was low, severe outcomes were common, PCR was scarce and slow, and government programs made them easy to get; home use surged after Omicron arrived in late 2021. Earlier studies — with the pre-Delta and Delta variants and few immune participants — found antigen tests highly specific but less sensitive than PCR, and closer to viral culture, which detects actively replicating virus (a sign someone is likely contagious), whereas PCR also picks up viral fragments. With more immunity and new Omicron variants, CDC re-examined their performance.

The study

Infected people and their household contacts were enrolled within 7 days of the first person's illness. For 10 days, participants kept daily symptom diaries and took two nasal swabs each day: one tested by RT-PCR and culture, the other with an at-home antigen test read by the participant.

Participants: of 354 people in 129 households, 236 (67%) tested positive by PCR — aged 2 months to 83 years (median 36), 56% non-Hispanic White, 59% female. 40% had a COVID-19 vaccine in the past 12 months, 35% had 2 or more doses longer ago, and 24% were unvaccinated; 43% had evidence of earlier infection. 93% had symptoms — 77% a cough, 66% fever.

Results

2,244 antigen results were reported. 61% of infected participants had at least one positive culture, and 69% at least one positive antigen test.

• Timing: positive antigen (59%) and PCR (83%) results peaked 3 days after onset; positive cultures peaked at 2 days (52%). Among people with symptoms, antigen positivity peaked at 65%, and among those with fever, at 80% on day 2.

Share of positive results by test type and day since onset. Figure from the CDC report.

Sensitivity of rapid antigen tests, overall and by symptoms. Figure from the CDC report.

What it means

• Antigen tests and culture caught a similar share of infections, both fewer than PCR. That suggests a positive antigen test likely signals contagious virus, so antigen tests can help people judge when they're no longer infectious as symptoms fade.
• The findings match earlier studies; an early 2021 study found 84% sensitivity against culture and 64% against PCR — differences possibly due to immunity, variants, the PCR's detection limit or sampling.
• Treatment can't wait: COVID-19 antivirals should start as soon as possible, within 5–7 days of symptoms. A false-negative antigen result can delay them, so PCR is the better test for people at higher risk. If PCR isn't available, follow the Food and Drug Administration's advice on repeat antigen testing.
• Use antigen tests once symptoms start — they perform poorly without symptoms — and stay home when sick, whatever the result, especially with cough or fever.

Limits: participants had mild to moderate illness and may not represent everyone infected; only one brand of antigen test was used; and onset for people without symptoms may be dated late if households enrolled after the first positive test.

Sources

Based on Sarah E. Smith-Jeffcoat, Alexandra M. Mellis, Carlos G. Grijalva and others, "SARS-CoV-2 Viral Shedding and Rapid Antigen Test Performance — Respiratory Virus Transmission Network, November 2022–May 2023," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain. Its social media graphic, built from stock photographs, is not reproduced.