Is the approach to anti-COVID-19 vaccination comparable to other anti-flu campaigns?

The majority of vaccines against respiratory infections are effective against symptomatic cases, but do not completely block infection. In the case of COVID-19, first results showed that the mRNA vaccines were very effective against symptomatic and asymptomatic infections, as well as against transmission. This news raised hopes that anti-SARS-CoV-2 vaccines could stop the spread of the virus. However, this optimism was dashed after the appearance of the Delta variant, which causes asymptomatic infections and sometimes moderate illness even in vaccinated individuals. After a period of relative stability, Delta caused an upturn in the incidence of COVID-19.

Current vaccines will clearly not completely eliminate SARS-CoV-2. In terms of future strategy, we can perhaps learn from the instance of the influenza virus. Flu and COVID-19 epidemics have numerous elements in common. Some strains of flu are able to spread rapidly, overloading health structures. The antigenic drift of influenza (generating variants), as well as the decline in immunity over time, also necessitates an annual booster jab. In fact, the vaccines are updated twice a year based on the recommendations of the World Health Organisation.

However, the efficacy of anti-COVID-19 vaccines is higher than 90% against symptomatic cases, while flu vaccines manage only 50 to 60%, and sometimes less. The priority is to limit the emergence of variants, severe complications, hospitalisations and death, but not to eliminate transmission and moderate illness. Taken as a whole, these priorities remind us of the current situation with the Delta variant and mRNA vaccines.

We need to learn to live with SARS-CoV-2 just as we do with flu. Regular vaccination will be crucial, since SARS-CoV-2 will remain with us and undergo antigenic changes, thus joining the other endemic coronavirus strains that reappear every year. We can base our approach on that of the flu model in order to deal with the situation, notably the public/private collaborations that determine the annual composition of vaccines. When evaluating their efficacy, the focus should be on reducing severe cases and mortality rather than on transmission and moderate cases. Although the proportion is small, the severe cases observed in vaccinated individuals underscore the importance of continuing to develop effective antiviral therapies that will not be affected by antigenic drift.