Question: I’m having my wedding in a few weeks and we have asked guests to take a covid test 72 hrs prior (in addition to other precautions). A few guests have pointed out updated information on rapid antigen tests. While I know pcr is the gold standard, I wonder about the use of rapid antigen tests for those who don’t have 3 days between travel and the event. Any thoughts?
Answer: Congratulations on your upcoming wedding! When it comes to testing, you’re right that PCR testing is more precise than antigen testing. Generally, antigen tests are pretty good at identifying cases in the early symptomatic period (see Q&A of 10/24/20), but not as good as PCR at picking up cases during early infection and 1+ week after infection. Even so, antigen tests could be a great addition to your medley of public health precautions. If I were you, I’d add antigen tests as an option for guests to use, with the push that they get tested twice– 3 days before the wedding and the morning of the wedding. And if anyone has had a known exposure or symptoms, I’d ask that they stick with the PCR test (although for someone with symptoms, I’d probably ask that they not come!). On this front, if time is of the essence, it’s good to remember there are a few sites that offer rapid molecular tests, which are quick turn-around tests that are provider-administered with sensitivity rates similar to PCR. If you want to read more on rapid antigen tests, here are a few relevant details:
A recent systematic analysis published in BMC Infectious Diseases, which synthesized results of 24 published studies, found that sensitivity*– the ability of a test to pick up all cases– of lateral flow assays (a type of antigen rapid test) varied dramatically by test type (Figure 1). Authors noted, “BD Veritor had the best sensitivity of 99.19% (95% CI 95.54–99.86%), though the sample size was small and it was only tested from a single centre study…. Panbio Abbott has been most thoroughly evaluated and noted a sensitivity of 78.41% (95% CI 76.78–79.96%) across over 2500 individual tests.” Other research has shown that sensitivity of antigen tests can be greatly increased if they are used every 3 days (reaching 98% in a small study). Many test kits that you can purchase at the drug store come with 2 tests, so this type of serial testing can be done with just one purchase. Finally, two days ago Scientific American published an article that is really informative and easy to read on this topic, The Smartest Way to Use Rapid At-Home COVID Tests.
*For a refresh of sensitivity/specificity, see Q&A of 4/15/20.
Figure 1. Sensitivity of different types of rapid tests (from BMC Infectious Diseases)
