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Arnaud Fontanet
π Health and biotech

“No normality without mass vaccination”

Arnaud Fontanet, Medical epidemiologist, Professor at Institut Pasteur, and Lecturer at CNAM

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 8th 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 

Contributors

Arnaud Fontanet
Arnaud Fontanet
Medical epidemiologist, Professor at Institut Pasteur, and Lecturer at CNAM

Professor at the Institut Pasteur and the Conservatoire national des arts et métiers, Arnaud Fontanet is a doctor of medicine (Paris V) and a doctor of public health (Harvard), specialising in the epidemiology of infectious and tropical diseases. Since January 2002, he has been head of the emerging diseases epidemiology unit at Institut Pasteur in Paris. He is also director of the Pasteur-CNAM school of public health and director of the global health department at Institut Pasteur. In 2018-9, he was the first holder of the newly created Chair of public health at the Collège de France. Since March 2020, he has been a member of the Covid-19 scientific council to the French government.