“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