Call it a weakly testing option
Would you buy life insurance that pays only if your death occurs in April through December but not in January through March? Would you agree to a monthly contraceptive injection that lets you get pregnant during the second and third weeks of each month? Of course not.
Then why should we rely on a weekly COVID viral test among the unvaccinated as protective against the spread of COVID-19 in the workplace or university when that weekly test predictably misses infections that began just a few days before the test?
Governments, employers and universities that rely on once-aweek COVID viral testing as an alternative to vaccination do exactly that: require a frequency of COVID viral testing that misses cases that then inevitably expose others to infection. The MTA, the state of Connecticut — and my university, City University — do this, and so do many others. The vaccination mandate President Biden for large private companies through the federal Occupational Safety and Health Administration may include a weekly testing option for those who refuse to get a shot.
They all mean well, of course, but the road to a resurgent pandemic is paved with good intentions.
Why is weekly testing not good enough? The answer is in sensitivity of our tests and in the speed at which the virus reproduces. During the initial incubation period of SARS-CoV-2, it eludes detection by current tests. After a person acquires the virus that causes COVID-19, the virus reproduces in cells and builds in numbers over a two-to-three day period before a positive result will register on a PCR or antigen test. A day or two after this viral buildup, the infected person becomes infectious and can spread the virus to others. This is the so-called silent infectious period, when the infected person poses a threat to co-workers or classmates.
All this, notably, occurs before the person develops COVID-19 symptoms. And if the person never develops symptoms, this period of threat can last a week or more.
Suppose someone is tested every Monday. If a person has picked up the virus over the previous weekend, say, at a restaurant, movie or other indoor gathering, a viral test upon returning to work on Monday will be negative. The quantity of virus in the body hasn’t multiplied enough yet to be detected.
By mid-week, though, the viral load will be high, and the person becomes infectious, unknowingly spreading the virus to others. They may continue to spread the virus until the following Monday when they undergo their next weekly test, and the infection is finally detected. Weekly testing has thus permitted the spread of undetected virus for most of the week.
In this same Monday testing scenario, the person infected over the weekend may develop symptoms by Wednesday or Thursday and, if tested at that point (based on those symptoms), tests positive and isolates, protecting others. But they still have that one-to-two-day silent infectious period before the symptoms arrive and may infect others before they finally get tested and then isolate.
In short, the once-a-week testing schedule represents a dangerous failure of testing. This is true no matter what day of the week someone has the test. It consistently fails to identify many infections in time and predictably allows many infectious people to remain in the workplace or classroom.
How about testing twice per week, say, on Mondays and Thursdays? Some countries and universities (for example, in Italy and at the New School and Harvard) now require such screening for unvaccinated people.
Twice per week testing, though not perfect, is far more protective than weekly testing. The person who is infected on the weekend days will test negative on Monday but will most likely test positive on Thursday. They may have become infectious on Wednesday, but by Thursday, their infection would be identified, leading to isolation and rapid cessation of risk to others. This testing schedule is especially useful in identifying early the large proportion of infected people who never develop symptoms.
You might wonder why we should not just test for COVID-19 virus every day. In fact, daily testing is possible and desirable in countries where testing is inexpensive and plentiful (for example, Germany and England). And it is excellent news that the Biden administration plans to spend $1 billion to make rapid self-administered test more available in the U.S. Daily testing might be ideal, but, for the moment, feasibility, cost and science support performing COVID virus testing twice per week for the unvaccinated. It would be a vast improvement over the current weekly testing regimen.