The Economist - USA (2022-01-15)

70 Science & technology TheEconomistJanuary15th 2022

Omicronandimmunity

The start of

something new?

V

ariantsvary, buthow much?Since

sars­cov­2  was  first  sequenced  at  the

beginning of 2020 dozens of versions have

been identified. Five have been designated

“variants of concern” by the World Health

Organisation (who). The latest is Omicron,

which was given its name in November last

year and looks set to become the dominant

form of the virus almost everywhere. 

One question occupying both scientists

and  politicians  is  whether  covid  vaccines

would work even better if they were updat­

ed to deal with novel variants. Up to and in­

cluding Delta, first identified in India, and

designated  a  variant  of  concern  in  May

2021, the answer has been “no”. But new re­

search, which has mapped differences be­

tween  all  of  the  important  versions  of

sars­cov­2,  suggests  that,  although  ad­

ministering  existing  vaccines  is  still  use­

ful, Omicron is so different from the others

that the answer might now be “yes”.

Researchers  in  the  Netherlands,  co­or­

dinated  by  Rogier  Sanders  and  Colin  Rus­

sell  of  the  University  of  Amsterdam  and

Dirk Eggink of the Dutch Public Health In­

stitute,  acquired  blood  samples  collected

from  51  unvaccinated  people  shortly  after

they  had  been  infected  with  various  ver­

sions  of  sars­cov­2.  These  included  the

original,  ancestral,  strain  and  the  Alpha,

Beta, Gamma and Delta variants. (Omicron

samples were not available.) They then as­

sessed  the  antibody  response  (“neutralis­

ing capacity”) of those samples against dif­

ferent antigens—in other words, different

versions  of  the  virus,  again  using  the  an­

cestral  strain,  Alpha,  Beta,  Gamma  and

Delta and, this time, Omicron.

By measuring the neutralising capacity

of  the  serum  of  each  participant  against

the  various  variants  and  applying  what  is

known  as  a  multidimensional  scaling  al­

gorithm, Dr Sanders, Dr Russell, Dr Eggink

and their colleagues were able to position

both the viruses and the serum samples on

an “antigenic map” (see chart). This is used

to  study  how  mutations  make  viruses

more  or  less  different  from  the  ancestral

strain, in a process called antigenic drift. In

such maps, one unit of distance is equiva­

lent to a two­fold change in neutralisation

titre  (a  measure  of  the  concentration  of

antibodies in the blood needed to neutral­

ise a virus). Samples plotted closer togeth­

er  are  more  similar.  Going  by  a  measure

conventionally used to group influenza vi­

ruses—a  distance  of  three  or  fewer  anti­

genic units—the researchers found that

Omicronwouldcountasthefirstofa new

groupofsars­cov­2.Whereasallwidely

circulating variantsbefore it,beingless

thanthree units apartfromeach other,

clusterasa singlegroup,Omicronismore

thanfiveunitsawayfromallothers.

A paper describingthisresearchwas

uploadedtomedRxiv, a researchportal,on

January3rd,buthasnotyetbeenpeer­re­

viewed.Theauthorsalsocautionthattheir

methodsvaryslightlyfromthoseconven­

tionallyusedtomapinfluenza.Neverthe­

lesstheyconcludethat“thechangeinneu­

tralisation between Omicron and other

variantsofsars­cov­2,includingthean­

cestralstrain,isstriking”.(Aseparatein­

vestigation,publishedonthesamedayin

Cell, reachesa similarconclusion.)DrRus­

sell cautions that the study’s findings

shouldnotbeinterpretedtomeanthatex­

istingvaccinations,designedforthean­

cestralstrain,areineffective.“Omicron’s

substantial reduction in cross­reactivity

withpreviousvariantsdoesn’tmeanthat

thereisnoreactivity.Thisisprobablywhy

boosting withcurrent vaccinesprovides

someprotection,”hesays.

AsmorepeoplecatchOmicronorare

vaccinated,somoreofthepopulationwill

havesomeprotectionthaninthepast.Oth­

er studieshavealso shownthatthe re­

sponseofanotherpartoftheimmunesys­

tem,itst­cells,seemslessaffectedbyOm­

icron’smutations. That is probably one

reasonwhyOmicronrarelycausessevere

diseaseanddeathinthosewhohaveac­

quiredimmunitythroughinfectionorvac­

cination.TheotheristhatOmicronitself

seemstobeinherentlylesslethal.But,just

astwicea yearthewhoorganisesexpert

reviews ofinfluenzaviruses andissues

recommendationsonhowtotweakvac­

cine compositions, Dr Russell proposes

somethingsimilarforcovidvaccines.For

maximumefficacy,hesuggests,vaccines

shouldbeupdatedassoonaspossible.n

The latest iteration of sars­cov­2 really

is different from those before it

The same, but different

Antigenic map of differences in antibody response

Source:“MappingtheantigenicdiversificationofSARS-CoV-2”,

byKarlijnvanderStratenetal.(2022,preprint)

↑Two-foldchangeinconcentrationofantibodies

neededforneutralisationofvirus

Asthedistanceincreases,

sodoesthedifference

inantibodyresponse →←

↑

↓

Alpha

Ancestralstrain

Beta

Delta

Gamma Omicron

Antigens(samples

ofvirusvariant)

Serum (blood sample),

by variant of past infection

and Revivicor,  a  regenerative­medicine

company  in  Blacksburg,  Virginia.  It  was

Revivicor  that  provided  the  genetically

modified pig for Friday’s surgery. The ani­

mal in question had a genome modified in

ten  ways,  to  optimise  the  chances  of  suc­

cess. Three genes had been removed to re­

duce  the  risk  of  a  human  antibody  reject­

ing  the  donor  organ.  A  fourth,  a  growth

gene, had also been knocked out, to ensure

the heart did not enlarge after transplanta­

tion. And six human genes had been add­

ed, to promote acceptance. 

In addition to the usual risks surround­

ing any heart transplant, there are a num­

ber of areas of concern that Dr Griffith and

his colleagues will be looking out for. One

is any hitherto­unknown rejection mecha­

nism. Another is the possibility that the or­

gan may transfer porcine viruses to its new

host.  The  pig  in  question  was  reared  in  a

sterile  environment  to  minimise  the

chance of that, but it remains a possibility.

Supporters  of  xenotransplantation

think its potential to improve lives is huge.

In America alone, over 100,000 people are

waiting  for  transplants  (though  the  vast

majority need a kidney rather than a heart).

In  2020  only  a  third  of  the  required  num­

ber of organs became available. 

In  theory,  pigs  can  be  bred  to  provide

humans  with  any  solid  organ,  though

some will be more complex than others. A

large  part  of  the  heart’s  function  is  me­

chanical,  but  other  organs  have  chemical

jobs that will be harder to replicate. More­

over, even assuming these barriers can be

overcome  and  successful  surgical  proce­

dures developed, most researchers still ac­

knowledge that scaling up xenotransplan­

tation  to  meet  the  world’s  demand  for  or­

gans  may  take  decades.Afterthis  news,

however,  the  chances  thatitwill  happen

eventually have increased.n

Lifesaver