Dear Sirs:

As all of you know well, it has repeatedly been alerted that the aged tends to suffer more severely than the young. Statistical data show more than fifteen percent of those aged over 80 and hospitalized due to the infection lose their lives if without any effective medical care.

Nevertheless, three of my acquaintances with their ages of eighty or more, who have got infected with CoV-2 during this year, wan their battles against the virus without, or with only little if any, difficulty:  They are a diabetic woman, age 80, her healthy husband, age 82, and a diabetic man, age 98！

One day in the beginning of September this year, the husband and his wife joined in a dinner party in downtown Tokyo.  Four or five days after the party, he felt a slight illness with which he thought of CoV-2 infection, had a PCR test, which was found positive. Then, his wife was tested, and was found positive, too.

For four or five days afterward, he had got some signs of Covid-19, i.e, dullness, low blood oxygen level, and some fever, but recovered soon. He was not hospitalized and did not take any medicine whole through this period.

His diabetic wife, who was compulsory hospitalized since she was regarded as a risky patient, did not particularly feel ill during hospitalization for ten days, and was discharged.

The 98 years old man went to a local hospital with his orthopedic problems, where he was exposed, unexpectedly and unfortunately, to an outbreak of CoV-2 within the clinic.  Being found PCR positive, he was moved from the local hospital to a hospital specialized for Covid-19 which is located far away from his home. He spent there alone for around two weeks without feeling any illness, except for a slight elevation of body temperature. Now he has come back to the local hospital and seems to be fine, as long as the viral disease is concerned.

So, how do you think?  What are the factor(s) that make these old persons so strong against CoV-2?   Looking for any scientific studies related to this personal experience, I have found statistic data showing that aged people are not uniformly sensitive, but 20 to 30 percent of them remain within ‘subclinical’ condition after infection (meaning that they do not feel illness so much as they want to see doctors), while many others suffer severely.

Another paper reports a case of identical diabetic twins with apparently similar body condition to each other, where the twins, being infected simultaneously with CoV-2, showed quite different courses of illness to each other: One became severely ill, turned to be housed in an ICU (intensive care unit), where she was barely saved with ECMO (extracorporeal membrane oxygenation), while her twin sister remained without almost any illness.

As to the puzzle of this unsolved question, there appear several theories, each with some epidemiological evidence, but not fully established yet. Yes, I myself have one in my mind. It is so thrilling to search in literature for any further evidence to test these theories.

hascross　mini-essay series no.1 December 31,  2020
Presented by Toshiharu Matsumura, Ph.D