Covid-19: What you need to know today
There’s long been a theory that the number of people infected with the Sars-CoV-2 virus, which causes Covid-19, is actually higher than that reported.Updated: Apr 25, 2020 07:27 IST
When there is no cure, metrics such as the prevalence of infection and immunity in a population become important.
Which is why the results of New York’s study of 3,000 people picked at random for an antibody test that were announced on Thursday are being studied around the world.
With the caveat that there are still question marks over the first phase of antibody tests for Covid-19 — it turns out there have been issues with the first phase of antibody tests for pretty much anything, including HIV-AIDS — the study found that around 21.2% of the sample in New York City tested positive.
New York City may be an outlier given its population density (the corresponding proportion for the state, in the same study, was 14%), but the study, which needs to be validated across a larger population is very significant: it means the extent of the infection is much larger than previously measured; it also means the fatality rates are much lower (in fact, much, much lower).
There’s long been a theory that the number of people infected with the Sars-CoV-2 virus, which causes Covid-19, is actually higher than that reported — one that has gained currency following confirmation that many infected people are asymptomatic and 97% of the cases (according to worldometers.info ) are mild. In New York City, for instance, this would mean that around 1.8 million people have been infected, didn’t know about it, and either didn’t fall ill or fought off an all-too-brief illness.
A similar study in France claimed that 6% of the French population was infected.
The New York study is important because it shows that antibody tests can be used to gauge prevalence of disease in a population. Some countries also want to use these tests to decide how and when to open up — a person with antibodies should, in principle, be immune to the disease and can safely return to work. Experts aren’t so sure because not enough about Covid-19 is known to assess just how long people with antibodies will remain immune to the disease.
Such tests, which are being refined and improved continuously, will also help measure if and when countries achieve herd immunity. This is the proportion of population that needs to be infected with the virus (and therefore become immune, at least in theory) to ensure that the virus doesn’t jump easily from person to person. Experts put the number at 60-65%.
The studies from France and New York show that it will be a while before that number can be reached.
Sars-CoV-2 is clearly a vexing virus — it is highly infectious, hasn’t mutated and weakened and died out like many other viruses before it have, and remains without a cure. Every promising line of prophylaxis and treatment has ended up failing. The latest among these is Gilead’s failed Ebola drug remdesivir. The Guardian reported that the drug didn’t work in its “first full trial”. A previous trial in China, the report added, came up with a similar result.
Adding to its vexatious nature is the discovery that while it infects more of a population than initially thought, the virus doesn’t infect enough to cause herd immunity.
Now, everyone is pinning their hopes on a vaccine trial that began on Thursday in Oxford. The vaccine, which uses a weak strain of a virus that causes a cold in chimpanzees, has generated excitement after one of the scientists involved in its development, Sarah Gilbert of the Jenner Institute, told media last week that she was 80% confident of the vaccine’s success. Everyone is hoping she is right.