“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