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I was listening to a virology expert on the Swedish radio yesterday. He said that there already were several corona viruses among humans that only affected children because basically all the adults were already immune. He said that he believed that SARS-CoV-2 will be added to this category in the future, which seemed logical to me. Basically SARS-CoV-2 will at some future time only affect children and give very little symptoms because all the adults will be immune.

By googling I found four viruses listed as "common corona viruses" that affects humans:

229E (alpha coronavirus)

NL63 (alpha coronavirus)

OC43 (beta coronavirus)

HKU1 (beta coronavirus)

1.Can something be said about how "common" these viruses are?

2.I mean if an adult for some reason has no immunity to one of these viruses how long will it take on average before he gets infected?

The reason I am asking is because if we know the answer to question 2 above for the four common coronaviruses one maybe can produce an educated guess for the likelihood for a person escaping the "first wave" of SARS-CoV-2 getting infected within a given time period after we have "herd immunity" against SARS-CoV-2.

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    $\begingroup$ I'd question pretty much anything else that "virology expert" says, since they seem to be well outside the mainstream understanding of these viruses. $\endgroup$ – Bryan Krause Apr 27 at 14:26
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    $\begingroup$ It was this guy: liu.se/en/employee/lensv66 Maybe people invited to public radio fell that their role is to calm the public rather than to be totally accurate. $\endgroup$ – Agerhell Apr 28 at 20:17
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The common [cold] coronaviruses are pretty common:

Four HCoVs (HCoV 229E, NL63, OC43, and HKU1) are endemic globally and account for 10% to 30% of upper respiratory tract infections in adults.

To pick a more detailed study in (ahem) Ghana:

This study sought to determine whether human coronaviruses (HCoVs) are associated with upper respiratory tract infections among older children and adults in Ghana. We conducted a case control study among older children and adults in three rural areas of Ghana using asymptomatic subjects as controls. [...]

Out of 1,213 subjects recruited, 150 (12.4%) were positive for one or more viruses. Of these, single virus detections occurred in 146 subjects (12.0%) and multiple detections occurred in 4 (0.3%). Compared with control subjects, infections with HCoV-229E (OR = 5.15, 95%CI = 2.24–11.78), HCoV-OC43 (OR = 6.16, 95%CI = 1.77–21.65) and combine HCoVs (OR = 2.36, 95%CI = 1.5 = 3.72) were associated with upper respiratory tract infections. HCoVs were found to be seasonally dependent with significant detections in the harmattan season (mainly HCoV-229E) and wet season (mainly HCoV-NL63).

enter image description here

Occasionally there are substantial outbreaks of common cold, e.g. as observed in Japan:

we conducted a longitudinal survey between 2010 and 2013 in Yamagata, Japan, to clarify the epidemiology of HCoVs using RT-PCR methods [...]. In 2011, we found that the monthly detection frequencies of HCoVNL63 were higher than 20% in January and February (28.5% and 25.3%, respectively), whereas those of the other HCoVs (HCoV-229E, -OC43, -HKU1) did not exceed 20%. In light of these findings, we continued the HCoV surveillance and, thus, captured data from the largest outbreak of HCoV-OC43 reported in the last 6 years. During the 2014–2015 influenza season in Yamagata, Japan, the monthly detection frequencies were approximately 30–40%.

Those percentages are from people reporting symptoms (and then swabbed.) The graph below (from the same paper) nicely shows the seasonality.

enter image description here

Monthly distribution of clinical specimens (A) and HCoVs (B) detected from patients with acute respiratory infections between January 2014 and March 2015, in Yamagata, Japan.

Question 2 is rather meaningless because immunity to common coronaviruses is short lived. See (also) this answer (esp. the 2nd table) to a related question putting the common coronaviruses immunity duration in perspective; reproducing just the table below (the relevant line for common coronavirus is the 1st below the break, i.e. 1st in the 2nd section of the table).

enter image description here

And I've managed to track down one of the primary studies on 229E long-term immunity (or rather lack thereof)

enter image description here

Although after 1 year concentrations of specific serum IgG and nasal IgA were still significantly raised in the infected group, they were much lower than at the maximum. [...] When challenged after 1 year all of the original uninfected group were infected and 6/9 of the infected group were reinfected. [...] In the infected group there were considerable individual differences. Some lost their antibody, particularly serum antibody, completely by 1 year, some did not.

And it's basically impossible not be exposed to a strain of the common cold coronaviruses at one point; one study on newborns found that interval to be 3.5 years, but that's probably an overestimation for adults.

all of the children had maternal anti-NL63 and anti-229E antibodies at birth that disappeared within 3 months [...] on average, HCoV-NL63 and HCoV-229E seroconversion occurs before children reach the age of 3.5 years.

The real question is whether Covid-19 will behave like the common coronaviruses or more like SARS and MERS for which it is suspected (from the detection of antibodies), but not certain that immunity lasts longer.

For the SARS and MERS coronaviruses, antibodies appear to persist for several years, but no studies have intentionally attempted to re-infect people, since these are deadly diseases.

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