First Glimpse of SARS CV2 Seroprevalence in Canada
As is to be expected the headline buried the good news Serology study estimates less than 1 per cent of B.C. was infected by first coronavirus wave. Excerpts in italics with my bolds.
B.C. Centre for Disease Control research also suggests province’s true infection rate is about eight times the rate based on reported cases
The study is the first in Canada to report infection rates based on seroprevalence, which is a measure of the presence in blood samples of antibodies produced to resist the virus.Determining exactly how many people in Canada have been exposed to COVID-19 is a key goal of the immunity task force the federal government set up in April.
Timothy Evans, a member of the task force and director of McGill University’s school of population and global health in Montreal, said the B.C. survey indicates the province’s deft management of the first wave of the pandemic resulted in very low exposure across its population.
“The low prevalence of population immunity suggests that continued vigilance and adherence to best practices to reduce risk of infection will be critical, especially in the context of the second wave of the pandemic,” Dr. Evans said.
He added that the eight-to-one ratio of actual to reported cases is consistent with international studies and that he expected a similar result across Canada. The survey was based on blood samples from more than 1,700 people in two periods, one in mid-March and a second in late May. The data were gathered anonymously from residual blood drawn from individuals at diagnostic clinics in B.C.’s Lower Mainland. The subjects were males and females of varying ages, including children.
Dr. Jha, who is leading a seroprevalence study that aims to sample as many as 10,000 Canadians, also said the individuals in the B.C. study may not be representative of the province’s population. For example, the study may be skewed toward healthy people who were having their blood tested as a precaution, or by those who were already ill.
It also captured the presence of antibodies in blood samples before and after the first wave but not during the peak in April. Another key piece of information the B.C. study does not provide – and was not designed to – is whether the individuals found to have antibodies for COVID-19 are now immune to the coronavirus and, if so, for how long.
Up to now, we have only been able to estimate the lethality of Covid19 by comparing death rates to confirmed cases. In Canada as of July 17, 2020, there were 8839 deaths of people with Covid19 compared to 109669 confirmed cases, or 8.1%. If the actual # of infections was 8 times higher, that ratio drops to 1% lethality. Furthermore, the ratio of deaths/cases ranged as high as 14% early June, and is now down to 3%. Factoring in the hidden infections reduced the current lethality to 0.4%.
Of course this is preliminary reporting while we await results from the nation-wide study.
via Science Matters
July 21, 2020 at 09:07AM