Are rapid tests for Covid reliable? What US Research Reveals

Since May 2022, the United States has been experiencing another spike in the number of Covid-19 cases.

High infection rates in Europe and Asia, along with the continued emergence of new subvariants, such as the BA.4 and BA.5, raise concerns that another outbreak may be on the way.

While demand for Covid-19 tests far outstripped supply at the start of the pandemic, many of us now have access to rapid home tests.

Home tests provide a quick and accurate result, but on the other hand many results are no longer reported to health authorities.

The advantage of these tests that are widely available to buy from pharmacies (without a prescription) is that individuals can quickly and conveniently know their infection status early on to prevent spreading the virus to others.

We are part of a team at the University of Massachusetts Medical School in the US that has been studying the performance of Covid-19 molecular (or PCR) and antigen tests for the past two years.

During this time, we’ve helped several companies generate the data they need to pass their products through the FDA’s emergency use authorization process, the US drug regulatory agency, and for commercial development.

We also carry out large-scale studies with real-world data to understand how rapid tests sold over the counter compare to PCR tests in detecting different variants of SARS-CoV-2, the virus that causes Covid-19, including among people. no symptoms.

We are also studying whether mass distribution of rapid antigen tests before an outbreak helps prevent the spread — and whether users of these tests are likely to report the results to health departments.

These studies are beginning to provide researchers like us with evidence about how these tests are performing and how we can use them to improve public health recommendations in the future.

Home tests and the omicron variant

When the omicron variant emerged in late November 2021, scientists reacted quickly to determine how PCR and rapid tests performed against this new variant.

Researchers have demonstrated that an infected individual will test positive on a PCR test one to two days before an antigen test.

This is because a PCR test works by amplifying the genetic material in a sample and is therefore able to detect extremely small amounts of viral material.

In contrast, a pharmacy test can only detect the viral proteins present in the sample.

At the beginning of the omicron outbreak, around December 2021, people wondered about the ability of rapid tests to detect the new variant.

In addition, some preliminary tests showed that rapid tests that identify the omicron variant had a delay of one to two days in the positive result, compared to tests performed with the delta variant.

This led to an FDA announcement on Dec. 28, urging caution in using tests to detect the omicron.

The role of rapid antigen tests

During this time, our group was working on a study looking at the performance of pharmacy tests in the general population.

We used the data from this study to evaluate the performance of these tests before and after the omicron became the dominant variant in the United States.

Our study, which has not yet been peer-reviewed, was unique in that it tested people for the virus that causes Covid-19 over two weeks, so we were able to observe emerging infections.

In our analysis of approximately 150 individuals who tested positive for SARS-CoV-2 during the study, we made two important observations.

The first is that pharmacy tests were able to detect the omicron variant as well as the delta variant.

The other is that serial tests — two tests performed 24 to 36 hours apart — are critical in the case of rapid tests.

That’s because we’ve observed that if a person had an infection detected by a PCR test for at least two days in a row, one or two of the pharmacy tests performed in the same period also detected the infection more than 80% of the time. In comparison, a single rapid test detected far fewer infections.

Previous research by our study team and others suggests that pharmacy tests are more likely to detect an infection among people who are actively contagious.

Pharmacy tests and notifications

In 2021, we assess whether mass distribution of pharmacy tests can reduce transmission of the virus by comparing new cases in Washtenaw County, Michigan, which has a population of 370,000.

Two communities made up of 140,000 of the county’s total population used more rapid tests and avoided an average of 40 Covid-19 cases a day during the delta outbreak.

Our findings suggest that rapid antigen testing is a critical public health tool that can help reduce the spread of disease during an outbreak.

But much of the research done to date on SARS-CoV-2 pharmacy testing has been done in controlled study settings.

We want to know if the performance of tests in a more realistic environment mirrors what is observed in clinical studies.

One question is whether people will report pharmacy test results to health departments.

We conducted several studies where people signed up using their smartphone, received the tests in the mail, took and reported the tests through a smartphone app.

Our initial analysis of data from the Michigan study, described above, shows that 98% of subjects agreed to submit test results to the state health department.

But only one in three participants most at risk of infection — for example, those who do not wear a mask in public and have not been vaccinated — have submitted their results.

Participants who carefully followed the instructions on the app reported more test results to their local health department than those who did not.

We also observed that negative test results were reported more than positive results.

In another study, we showed that incentives make a difference when reporting test results.

Sites with reporting incentives, such as cash payments, demonstrated significantly higher levels of reporting to the state health department than sites without incentives.

In total, 75% of the results recorded in the app were reported. In all communities, positive tests were significantly less reported than negative ones.

These results indicate that app-based reporting with incentives can be an effective way to increase rapid test notification for Covid-19.

However, increasing app adoption is an important first step.

These studies are ongoing and we continue to get more information about how people use rapid antigen tests.

If you are interested in contributing to this science, you can see if you are eligible for a study.

*Nathaniel Hafer is an assistant professor of molecular medicine at UMass Chan Medical School, USA. Apurv Soni is an assistant professor of medicine at the same institution.

This article was originally published on the academic news site The Conversation and republished here under a Creative Commons license. Read the original version here (in English).

‘This text was originally published at https://www.bbc.com/portuguese/internacional-61948938’