“No normality without mass vaccination”

How is the pan­dem­ic expect­ed to evolve in the upcom­ing months?

Until the end of Decem­ber 2020, we expect­ed the first trimester of 2021 to be dif­fi­cult due to weak immu­ni­ty in the pop­u­la­tion as well as the win­ter peri­od, which increas­es the spread of res­pi­ra­to­ry virus­es and gath­er­ings for the hol­i­day sea­son. In France, 12% of the pop­u­la­tion has been infect­ed so far. But we will need more than 50% to be immu­nised through vac­ci­na­tion or nat­ur­al infec­tion if we are to stop the virus from cir­cu­lat­ing in an epi­dem­ic way. 

The gen­er­al idea was that with the arrival of spring and warmer weath­er, and vac­ci­na­tion of peo­ple at risk, we could grad­u­al­ly return to a more nor­mal life. How­ev­er, the tables have turned since the emer­gence of VOC 202012/01 in the UK. Trans­mis­si­bil­i­ty of this SARS-CoV­‑2 vari­ant is 50% high­er than the reg­u­lar virus. Despite exist­ing mea­sures in the UK, the num­ber of cas­es has rapid­ly increased since Decem­ber 2020 and the hos­pi­tal ser­vices have reached sat­u­ra­tion, forc­ing the gov­ern­ment to impose a strict lock­down at the begin­ning of Jan­u­ary 2021. The same sce­nario was observed in Ireland. 

It is more trans­mis­si­ble, but does not seem more path­o­gen­ic. The first stud­ies sug­gest that peo­ple infect­ed last year, or those who are already vac­ci­nat­ed, would be pro­tect­ed in the same way against this vari­ant. Its emer­gence could be due to an accu­mu­la­tion of muta­tions dur­ing a chron­ic infec­tion in patients with severe immune defi­cien­cy, or to immune eva­sion when the virus is sub­mit­ted to strong selec­tive pres­sure in areas of high trans­mis­sion. This is what might have occurred in South Africa and in Brazil where two oth­er vari­ants emerged. These two vari­ants are more alarm­ing; not only are they more trans­mis­si­ble, but they evade the immune response induced by a pre­vi­ous infec­tion or by cur­rent­ly used vaccines.

The pro­por­tion of VOC cas­es in France was esti­mat­ed to be 3,3% on Jan­u­ary 8^th 2021. Giv­en a 50% increase per week, we can expect VOC 202012/01 to become the main vari­ant by the end of Feb­ru­ary – begin­ning of March. We will need to take dras­tic mea­sures before then to slow its pro­gres­sion and work against the clock to vac­ci­nate the most vul­ner­a­ble peo­ple. Vac­ci­na­tion will start with peo­ple aged over 75 years old and front­line health­care work­ers. In the sec­ond trimester, vac­ci­na­tion will be extend­ed to include all peo­ple who are at risk of devel­op­ing a severe form of the dis­ease: over 50s and peo­ple with comor­bidi­ties. After­wards, the entire pop­u­la­tion can be vac­ci­nat­ed in the sec­ond half of the year.

When will we reach a lev­el of herd immu­ni­ty capa­ble of stop­ping cir­cu­la­tion of the virus?

There are some uncer­tain­ties relat­ed to vac­cines: an uncer­tain pro­duc­tion capac­i­ty, high demand and mod­er­ate accept­abil­i­ty of the vac­cine in France. Last Decem­ber, more than half of French peo­ple did not want to be vac­ci­nat­ed. This num­ber will need to be reassessed once we have demon­strat­ed that vac­ci­na­tion is well tol­er­at­ed. With­out mass vac­ci­na­tion, there can be no return to a nor­mal social and eco­nom­ic life. 

Last Decem­ber, more than half of French peo­ple did not want to be vaccinated.

Is cir­cu­la­tion of oth­er dis­eases reduced by restric­tions imposed on the pop­u­la­tion? Or, on the con­trary, is a resur­gence of patho­genet­ic agents due to the increas­ing prox­im­i­ty between humans and ani­mals to be expected?

Thanks to the health mea­sures, a decrease in the cir­cu­la­tion of the influen­za virus, the res­pi­ra­to­ry syn­cy­tial virus and virus­es respon­si­ble for gas­troen­teri­tis has been observed. The absence of influen­za this year could result in a more severe epi­dem­ic next year, because immu­ni­ty in the pop­u­la­tion will not have been “boost­ed” this win­ter sea­son, as is usu­al­ly the case. Gen­er­al­ly speak­ing, these new health habits will be ben­e­fi­cial in the long-term for populations. 

Regard­ing the emer­gence and spread of new virus­es, these are linked to two phe­nom­e­na. First, cross-species trans­mis­sion includes muta­tion of infec­tious agents from ani­mal to human hosts. Sec­ond, the sub­se­quent spread in the form of an epi­dem­ic. As such, all fac­tors that lead to increased con­tact between humans and ani­mals, as well as high­er pop­u­la­tion den­si­ty and mobil­i­ty, are like­ly lead to a rise in the num­ber of epi­demics. In that respect, poul­try or pig fac­to­ry farms serve to incu­bate new influen­za virus­es, which are a threat to human pop­u­la­tions. Add to that, an increase in den­si­ty of viral vec­tors like insects, such as mos­qui­toes; a rise that is part­ly due to glob­al warming. 

Among these mos­qui­toes, Aedes egyp­tii, is a very com­pe­tent vec­tor capa­ble of trans­mit­ting arbovirus­es such as yel­low fever, dengue, chikun­gun­ya or zika. In tem­per­ate areas, a relat­ed species, Aedes albopic­tus, is now well estab­lished in the South of France and has been respon­si­ble for the trans­mis­sion of import­ed cas­es of dengue, chikun­gun­ya and zika in France.

The SARS-CoV­‑2 pan­dem­ic took the whole world by sur­prise. How can we pre­pare for the emer­gence of new viruses?

Viral out­breaks have always tak­en us by sur­prise. They often hap­pen in unex­pect­ed places. For exam­ple, the H1N1 influen­za virus out­break began in Mex­i­co (2009) while influen­za virus­es often came from Chi­na. I am also think­ing of the MERS coro­n­avirus which appeared in the Gulf states and for which camels were the reser­voir. The West African Ebo­la out­break in 2013 and 2014 also came as a sur­prise because Ebo­la out­breaks are usu­al­ly found in Cen­tral Africa. 

Final­ly, the Zika virus start­ed in South-East Asia then spread through the Pacif­ic and to Latin Amer­i­ca from 2013 to 2015. All this means that our inabil­i­ty to pre­dict the emer­gence of new virus­es com­pels us to imple­ment a high­ly respon­sive sur­veil­lance sys­tem to inves­ti­gate an emerg­ing out­break as soon as pos­si­ble. It is most unfor­tu­nate that the dras­tic mea­sures tak­en in Chi­na against SARS-CoV­‑2 in Wuhan were delayed by a month when it is clear that Chi­na was even­tu­al­ly able to elim­i­nate the virus from its territory.

In the future, we will need to act pre­ven­tive­ly by close­ly mon­i­tor­ing the cir­cu­la­tion of infec­tious agents in ani­mals and also lim­it­ing ani­mal-human con­tact in con­texts where the emer­gence of new path­o­gen­ic agents is to be feared. This involves, for exam­ple, hunt­ing wild ani­mals or indus­tri­al farm­ing of poul­try and pigs.

Interview by Clément Boulle