Covid-19: RAT test right before travel is better than 3-day old RT-PCR , says study

Indian virologists agree with the study when it suggests repeated testing to compensate for the low sensitivity of the RAT.

ByChetana Belagere

Published Jul 30, 2022 | 2:16 PMUpdatedJul 30, 2022 | 4:17 PM

Covid-19 test before Travel

The Covid-19 test done 72 hours before travel in many countries, including India, is not enough to stop the transmission of the virus, according to a Yale School of Public Health study.

The study suggested that the test be done on the day of travel.

They also found that a Rapid Antigen Test (RAT) done hours before travel is more effective in reducing transmission than an RT-PCR test done days before the trip.

10 times more effective

According to the Yale epidemiologists, testing on the same day of travel or a social gathering reduced transmission by around 40 percent.

Rapid Antigen Test kit (RAT) (Creative Commons)

Rapid Antigen Test kit (RAT) (Creative Commons)

The study, published in the International Journal of Public Health, found that transmission was reduced only by about 4 percent when tested 72 hours before arrival when compared to not testing at all.

According to the study, the risk of transmission potentially decreases up to 46.7 percent if the Covid-19 test is done closer to travel time.

Small traces go undetected

The researchers stated, “Policies that require people to have a negative Covid-19 test within 72 hours or more of their arrival at a location — which many countries enforce for travellers — hardly help.”

They explained that the disease has a very short period when it is highly transmissible. A RAT, if taken early, may fail to detect faint traces of the virus before it builds up to show positively in the test.

However, as the virus grows exponentially, the person’s viral load could surge after a little while.

Interestingly, they assessed more than a dozen varieties of RAT kits, including home test kits, and found that they were more effective than RT-PCR tests.

While RT-PCR takes longer than 12 hours to produce results, the test taken just hours before travel or a social gathering using RAT is more effective in reducing transmission.

Opinion of Indian experts

Dr Shahid Jameel, virologist and former chairperson of The Indian SARS-CoV-2 Consortium on Genomics (INSACOG), told South First, “Well, it makes intuitive sense — the closer you test on arrival, the better it is. It has already been shown that repeat testing with RAT is better than one-time PCR testing. The repeats make up for lower sensitivity.”

However, explaining the problems with testing on arrival, he said: “Testing on arrival still leaves an infected person getting on a plane in a closed, poorly-ventilated space and potentially infecting others.”

Instead, he said, testing on departure at airports would be a better option, with travel insurance covering anyone who tests positive. It would require widely available rapid tests with good sensitivity.