resistance

Levels of protective antibodies in people wane "quite rapidly" after coronavirus infection, say researchers.

Antibodies are a key part of our immune defences and stop the virus from getting inside the body's cells.

The Imperial College London team found the number of people testing positive for antibodies has fallen by 26% between June and September.

They say immunity appears to be fading and there is a risk of catching the virus multiple times.

More than 350,000 people in England have taken an antibody test as part of the REACT-2 study so far.

In the first round of testing, at the end of June and the beginning of July, about 60 in 1,000 people had detectable antibodies.

But in the latest set of tests, in September, only 44 per 1,000 people were positive.

It suggests the number of people with antibodies fell by more than a quarter between summer and autumn.

"Immunity is waning quite rapidly, we're only three months after our first [round of tests] and we're already showing a 26% decline in antibodies," said Prof Helen Ward, one of the researchers.

The fall was greater in those over 65, compared with younger age groups, and in those without symptoms compared with those with full-blown Covid-19.

The number of healthcare workers with antibodies remained relatively high, which the researchers suggest may be due to regular exposure to the virus.

Antibodies stick to the surface of the coronavirus to stop it invading our body's cells, and attract the rest of the immune system.

Exactly what the antibody drop means for immunity is still uncertain. There are other parts of the immune system, such as T-cells, which may also play a role.

However, the researchers warn antibodies tend to be highly predictive of who is protected.

Prof Wendy Barclay said: "We can see the antibodies and we can see them declining and we know antibodies on their own are quite protective.

Can we develop a herd immunity to Covid-19?

Experts say at least 50%-60% of exposure is required for herd immunity, where prevalence of exposure, and/or a vaccine, drastically reduces transmission of the virus. The CDC is careful to point out, however, that it doesn't know if the presence of antibodies prevents reinfection by the coronavirus. It appears that infection only gives a limited-time resistance, and a relatively weak resistance at that, so herd immunity may not be possible with Covid-19

Coronavirus infections in the United States are far higher than what has been confirmed, although the number of Americans who have been exposed is far below what is required for widespread immunity, according to data released by the Centers for Disease Control and Prevention. The CDC estimated the number of infections is about 10 times higher than the confirmed cases, based on blood samples analyzed for antibodies in 10 regions. Those regions included the New York City metropolitan area, parts of Washington state, Utah, south Florida and Missouri. Samples were taken from more than 16,000 people through the spring. Researchers relied on samples taken for routine tests, such as cholesterol tests, with more than a third coming from those aged 65 or older. Results for two rounds of sampling for eight of the 10 regions were released by the CDC. All the regions surveyed showed differences in estimates arrived at through the survey and confirmed cases. In Missouri, for example, that difference was 24 times in April. Though by the second round of sampling, in late May, that dropped to 13 times.

Basically we don't know yet whether or not infection with Covid-19 provides us with a resistance or an immunity to re-infection. It appears from the limited testing done so far that only a short-lived relatively weak resistance is obtained from infection; a resistance that is rather like the resistance obtained from catching the flu. First, scientists discovered patients who had recovered from infection with Covid-19, but mysteriously didn’t have any antibodies against it. Next it emerged that this might be the case for a significant number of people. Then came the finding that many of those who do develop antibodies seem to lose them again after just a few months.

This means that once infected with the coronavirus, after you recover, you can probably become infected again, or re-infected. This makes it even more critical that we SLOW the spread of the coronavirus, STOP the spread of the coronavirus, and try to SLAY (Eradicate) the virus completely, until such time that we have found an effective vaccine, or developed another way to gain a real immunity to the coronavirus. SSS - Slow, Stop & Slay!

In more scientific terms:

Antibody (Ab) responses to SARS-CoV-2 can be detected in most infected individuals 10-15 days following the onset of COVID-19 symptoms. However, due to the recent emergence of this virus in the human population it is not yet known how long these Ab responses will be maintained or whether they will provide protection from re-infection.

Studies show that a transient (temporary) neutralizing antibody response (nAb) is a feature shared by both a SARS-CoV-2 infection that causes low disease severity and the circulating seasonal coronaviruses that are associated with common colds. Stronger resistance is usually obtained from having a more severe form of Covid-19 (SARS-CoV-2), and lower levels of resistance are usually obtained from suffering milder forms of infection.