Immunity to coronavirus lingers for months, study finds

(CNN)Immunity to Covid-19 infection lingers for at least five 
months, researchers reported -- and probably longer than that.

While the report may seem confusing and contradictory to a 
similar report out of Britain this week, it really isn't. 
People's bodies produce an army of immune compounds in response 
to an infection and some are overwhelming at first, dying off 
quickly, while others build more slowly.

The new report out Wednesday shows 90% of people who recover 
from Covid-19 infections keep a stable antibody response.

"While some reports have come out saying antibodies to this 
virus go away quickly, we have found just the opposite -- that 
more than 90% of people who were mildly or moderately ill 
produce an antibody response strong enough to neutralize the 
virus, and the response is maintained for many months," Florian 
Krammer, a professor of vaccinology at the Icahn School of 
Medicine at Mount Sinai, who led the study team, said in a 
statement.

"This is essential for effective vaccine development."

The team looked at the antibody responses of more than 30,000 
people who tested positive for Covid-19 at Mount Sinai's Health 
System between March and October. They characterized their 
antibody responses as low, moderate or high. More than 90% had 
moderate to high levels, or titers, of antibodies to the spike 
protein of the virus -- the structure it uses to grapple the 
cells it infects.

They then closely studied 121 patients who recovered and donated 
their plasma -- once three months after they first developed 
symptoms, and again five months later.

They did see a drop-off in some antibodies. But others 
persisted, they reported in the journal Science.

"The serum antibody titer we measured in individuals initially 
were likely produced by plasmablasts, cells that act as first 
responders to an invading virus and come together to produce 
initial bouts of antibodies whose strength soon wanes," said Dr. 
Ania Wajnberg, director of Clinical Antibody Testing at the 
Mount Sinai Hospital.

"The sustained antibody levels that we subsequently observed are 
likely produced by long-lived plasma cells in the bone marrow. 
This is similar to what we see in other viruses and likely means 
they are here to stay. We will continue to follow this group 
over time to see if these levels remain stable as we suspect and 
hope they will."

Antibodies are not the only protection the immune system musters 
against infection, but they are an important first line of 
defense.

"Although this cannot provide conclusive evidence that these 
antibody responses protect from reinfection, we believe it is 
very likely that they will decrease the odds ratio of 
reinfection," the team wrote.

Covid-19 has only been around for a little under a year, so 
scientists are still learning about it. Stories of people 
becoming infected more than once are mostly anecdotal, and few 
and far between.

There's obvious concern about this. It would be far better for 
getting rid of the pandemic if people developed permanent 
immunity to the virus after an infection. And, of course, 
immunity would be vital for a vaccine to work well.

It happens with other viruses. Measles is an example. One bout 
of measles usually leaves someone immune for life -- an effect 
known as sterilizing immunity. The same was true for smallpox, 
before that virus was eradicated in the 1970s by a global 
vaccination campaign. And proper vaccination against measles and 
smallpox completely protects against infection.

But respiratory viruses such as influenza are trickier. People 
can catch flu over and over again and flu vaccines generally 
provide only partial protection against infection and severe 
disease. Part of that's due to flu's tendency to mutate.

Coronaviruses seem to fall in between. They can cause the common 
cold, but because they are not usually deadly, they are not as 
well studied. Until Covid-19's deadly cousin SARS came along, 
there was little interest in coronaviruses.

Still, there is evidence that people can and do develop some 
immunity to coronaviruses.

"We know from work with common human coronaviruses that 
neutralizing antibodies are induced, and these antibodies can 
last for years and provide protection from reinfection or 
attenuate disease, even if individuals get reinfected," Wajnberg 
and colleagues wrote.

"It is still unclear if infection with SARS-CoV-2 in humans 
protects from reinfection and for how long."

The next important step, they said, will be to establish what 
are known as correlates of protection. These are compounds that 
can be measured in the blood that will tell doctors whether 
someone is immune -- so that it won't be necessary to wait and 
see if they get infected again after one bout, or after getting 
a vaccine.

https://www.cnn.com/2020/10/29/health/covid-immunity-lingers-
months-wellness/index.html