Whither the coronavirus?

Whither the coronavirus?

Whither the coronavirus?

I started to write this letter in early March but realized there was too little known about the trajectory and characteristics of the SARS-CoV-2 (novel coronavirus) at that time.

The current public health restrictions in place serve to slow the rate of spread, avoiding overloading the health care systems and the mortuaries for those who are unfortunate enough to fall gravely ill or die. It does little to alter the number of people who will eventually become infected.

In the case of SARS-CoV-2, almost nobody yet has immunity so each infected patient passes it on to two (or more) others. The math is relentless; the series goes 2, 4, 8, 16, 32, 64... as more and more people become infected. Where does it stop? Once there are enough people who have gained immunity, and the propagation rate falls below 1:1, the infection peters out.

Polio, smallpox, and measles are viral diseases we attacked with effective vaccines, isolating patients and creating a ring of defense around the patients by vaccinating known contacts.

How does this work? Once an infected person has a vanishingly small chance of meeting and infecting a non-immune individual, the epidemic dies out. If enough people are vaccinated or have survived the disease, we approach ‘herd immunity’ where there are few or no chances for the virus to be passed on to an unprotected person.

What about SARS-CoV-2? It belongs to the same family that causes the common cold, SARS, and MERS. We were able to stamp out SARS and MERS through strict isolation of patients combined with rigorous contact tracing, limiting the known cases to under 10,000 in each case.

In both instances, early identification and isolation limited the spread of SARS and MERS, plus they both had a high mortality. With a high mortality rate there are fewer infected people circulating in the general population, allowing health care systems to isolate and stamp out any potential epidemic.

Compare this to Ebola, where the disease is both deadly and swift. Most victims, once they exhibit symptoms, are likely to die very quickly, limiting how far the infection can spread. As another comparison point, the dreaded Spanish Flu of 1918-20 had a mortality rate of ~2.5% and was the last great pandemic that swept the world, contributing to the end of World War I.

SARS-CoV-2 is significantly different from SARS, MERS, the Spanish Flu and Ebola. With SARS-CoV-2 asymptomatic people can transmit the virus to others and the mortality rate is somewhere between 1% and 3.5%, meaning there are many more chances for the infection to be transmitted before a patient either shows symptoms or succumbs.

The early detection was ignored or suppressed, allowing the virus to gain a wide foothold, first in China, and then around the world. Hence the rapid rates of spread.

Will there be a vaccine or future immunity to the SARS-CoV-2?

The jury is out on whether exposure to the current SARS-CoV-2 imparts immunity. The common cold is part of the coronavirus family, and we know that there has never been an effective vaccine developed against the common cold as it mutates rapidly enough to evade the immune system’s defenses.

If SARS-CoV-2 follows the pattern of the common cold, then people may become infected with a future variant and there will be no general ‘herd immunity’ developed against SARS-CoV-2 or its descendants.

This does not bode well for the development of a future vaccine. If prior infection or a vaccine imparts immunity to a specific variant of SARS-CoV-2 then each subsequent season will see another rise in infections and victims to the next variant.

This dismal scenario harks back to the pre-antibiotic days when there were no cures for scourges such as tuberculosis or typhoid or syphilis or sepsis and other bacterial diseases. The only solutions available were public health measures to isolate victims and prevent them from passing on the disease.

As with other infectious and contagious diseases, there is a percentage of the population that successfully rebuffs the ravages of the virus, while others becomes seriously ill and some die.

Until a vaccine is developed against SARS-CoV-2 it appears there will be an ongoing level of infection that afflicts a steady portion of the population each year.

It may well end up like the current situation with the influenza vaccine where each season we have to develop versions that are the closest match to the variants that are expected to emerge that year. But every year lots of people get the flu and many thousands die.

As of May 10, 2020, there have been two variants of the SARS-CoV-2 virus that allow it to bind to and infect human cells. One variant has been found in 788 samples, and the other in 32.

Michael Wycombe

Napa

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