covid-19 triggers a strong immune response in most pplz. yet several recent studies envisaged that the amounts of antibodies in those recovering from the virus appear to decline within a few mnths of infection. the findings set off a frenzy of speculation that immunity to the virus may not last long, throwing cold wata on hopes for a vaccine. many scis say such worries are overblon, however.
a jun 18 nature med study conducted witha lil group of patients in china showed that in both asymptomatic and symptomatic individuals with covid-19, antibody lvls dropped significantly during recovery—and that the lvls became undetectable in 40 % of the asymptomatic group. a preprint study by researchers in england twas' posted online in mid-jul similarly demonstrated that antibody lvls declined substantially within a few mnths of infection and that pplz with less severe illness had fewer antibodies. and most recently, a lil study, published on jul 21 inna new england journal of med, found a “rapid decay” in antibodies among individuals with mild cases of covid-19.
these results may sound universally grim. but several experts sci american spoke with said they thought that the declines were not as scary as initially portrayed, that some reduction in antibodies is normal and expected and that antibodies are just one piece of the immunity puzzle. evidence from other viruses and animal studies of sars-cov-2 infection provide reason for optimism, they add. that assessment is no doubt reassuring for vaccine developers, some of whom are already racing ahead with large-scale clinical trials. 1-ly longer follo-up studies of pplz infected w'da novel coronavirus will show whether antibodies confer lasting protection, however.
the human immune system consists of two pts: the innate immune system mounts a nonspecific response to invaders that occurs within hrs of infection. in contrast, the adaptive immune system launches a targeted reaction to a pticular pathogen, which can take weeks or mnths to develop. the latter system consists of 3 pts: antibodies, b cells and t cells. together they recognize and fite off the invader and can store a memory o'it in case of future infection (vaccines similarly work by creating a fake “memory”). somd' antibodies, known as neutralizing antibodies, can bind to a specific pt offa pathogen and deactivate it. scis hypothesize that these antibodies’ presence in pplz who ‘ve had covid-19 maybe one key signal of immunity.
the recent studies documenting patients’ antibody decline ‘ve triggered some scary headlines proclaiming that any immunity to covid-19 maybe short-lived. inna nejm study, otto yang, a professor of med and associate chief of infectious diseases atta david geffen school of med atta university of california, los angeles, and his colleagues measured antibodies in 34 pplz, the large majority of whom had clinically mild coronavirus infections, at an μ of 37 and 86 dys after symptoms appeared. “wha’ we saw was that the amount of antibodies gainsta virus dropped very dramatically in that time period”—by bout ½ every 36 dys, he says. (the paper originally described a ½-life of 73 dys, but this fig was found to be a mathematical error.) yang adds a few caveats: scis do not know if antibodies are protective against sars-cov-2 infection—although that possibility is a reasonable guess—or how much protection they mite confer. and they aint certain they are measuring the rite type of antibodies. nevertheless, he says, “the decline that we see is strikingly fast.”
other scis interpret the decline as less worrisome and in line with that envisaged in other viruses. in reference to the nejm study, florian krammer, a professor of microbiology atta icahn school of med at mount sinai, tweeted, “i fail to see the rapid decay here.” using a test developed by krammer and his team, a preprint study led by his colleague ania wajnberg found a much + modest decrease in antibodies. in some cases, pplz who had fewer antibodies at 1st even showed a lil increase over time.
seeing a slite reduction in antibodies is fairly normal, says wajnberg, an associate professor atta icahn school of med. “frankly, that’s not that surprising, cause you’re not sick any+,” she says. once a'pers has successfully fought off the infection, you ‘d expect his or her antibodies to approach a loer, baseline lvl. if that individual was reinfected, the b cells ‘d then ramp up the № of antibodies again, wajnberg says. or maybe that baseline lvl itself ‘d prove enough to be protective. “wha’ we don’t wanna see is: two weeks l8r, [antibodies] go to zero. honestly, that ‘d be very unexpected,” wajnberg adds. but'a fact that antibodies wane over time aint shocking, she says.
viral immunologist zania stamataki agrees. “the data onna decline of the antibodies aint scary. we’re seeing a tiny drop, which is quite expected,” says stamataki, a senior lecturer atta university of birmingham’s institute of immunology and immunotherapy in england. “i don’t think thris this really rapid decay like pplz ‘ve reprted.”
yang stands by his interpretation offa steep decline, saying it agrees well w'da nature med study and english preprint paper. he says the reason for disagreement may cogitate the pops bein’ studied. yang and his colleagues looked at pplz with clinically mild infections who had loer initial lvls of antibodies, whereas those who ‘ve higher lvls to start with “may actually also ‘ve + persistent antibodies,” he says.
stamataki and others caution that it remains to be seen whether any lvl of antibodies can shield against reinfection. “the fact that we can pick up antibodies in patients that ‘ve been infected with coronavirus does not mean t'they are protected,” she says. “it means'dat they can recognize the virus and make the rite immune response that ‘d potentially be protective inna future.” researchers still do not know wha’ amounts and types of antibodies will prevent reinfection 6 or 7 mnths l8r, “b'we ll'soon find out,” she adds.
scis ‘ve focused on antibodies cause they are relatively easy to measure witha blood test and maybe helpful as a treatment for covid-19. but'a adaptive immune system also involves t cells, which may mount a strong response to the novel coronavirus even if antibodies ‘ve waned. in may alessandro sette and shane crotty, both atta la jolla institute for immunology, published a study showing that sars-cov-2 produces a strong t cell response, pticularly to the virus’s “spike” protein, which it uses to gain entry to cells. and a preprint study by researchers atta karolinska institute in sweden found such responses in pplz with mild or asymptomatic covid-19, including when antibodies were undetectable. so even without antibodies, t cells ‘d keep a record of the infection. but its strength may depend on that infection’s severity. “the memory is proportional to the perturbation to the insult—how much offa scare the immune system has,” sette says. “if it’s a very mild infection, it mite not create enough of an immune response, inna 1st place, to create a long-lasting memory.” in fact, stamataki says, tis possible that some pplz may clear sars-cov-2 using the innate immune system—without developing any memory o'it. iffey then encountered the virus again, they ‘d potentially get covid-19 a 2nd time.
there ‘ve been a № of anecdotal reprts of pplz gettin reinfected w'da novel coronavirus, but no substantive proof s'been established. there are other explanations: pplz with weak immune systems mite not be clearing the virus totally, or tests mite be picking up remnants o'it tha're not infectious, stamataki says. while true reinfection aint impossible, it ‘d likely occur in 1-ly a lil minority of pplz, she adds.
scis still do not know wha’ lvl of immune response mite be protective against future infection. 1-ly longer-term studies ll'be able to answer that ?. wajnberg says her colleague viviana simon, a professor of microbiology atta icahn school of med at mount sinai, is currently leading a study to monitor a few hundred health care workers, with and without antibodies, ‘oer the course offa yr or two to see who gets covid-19 and who does not. yang says he and his team plan to continue monitoring + than 60 pplz for a yr swell.
inna short-term, though, animal research offers some clues. one study found that monkeys that were previously infected w'da novel coronavirus and developed antibodies did na'get sick when they were l8r reexposed. but monkeys aint humans, course. and deliberately exposing pplz to the virus rezs clear ethical issues, so we will likely ‘ve to w8 for + data to accumul8 ‘oer the nxt few mnths. “we nd'2 be patient,” sette says.
original content at: rss.sciam.com…
authors: tanya lewis