If the Covid pandemic seems to be marking time, it is not over for all that… After three years, it is however possible to take a step back on five major points which have raised many questions and debates, both about the virus than ways to fight it.
All viruses evolve over time, including Sars-CoV-2. Many variants have been identified and are classified by the WHO as “Variants of Concern” (VOC) or “Variants to Watch” (VOI) – these are the famous Alpha, Delta or more recently Omicron… which punctuated the news in 2021 and 2022, and today considered “formerly worrying”.
Since early 2022, the Omicron variant has dominated the world, along with the BA.5 sublineage. The strength of the latter lies in its ability to escape the immune protection induced by a first infection (by BA.1, etc.) and/or a previous vaccination. It tends to be replaced by the XBB.1.5 sub-lineage, coming from the United States and classified VOI.
Variants whose name begins with the letter “X” are said to be recombinant because they result from the genetic mixing of two previous variants – in this case between two sub-lineages of BA.2 for XBB.1.5. Recombination is a means of evolution of the virus just like a “simple” mutation, which corresponds to a genetic modification of the virus.
Variants have long been characterized by their place of emergence. The typologies by Greek alphabet (VOC) and by compound alphabet (VOI) then replaced the stigmatizing initial geographical denomination (variants “English”, “Indian”, etc.). Although the places of emergence of the new variants are varied, their rapid diffusion on a planetary scale obscures this aspect.
The elderly and vulnerable are more at risk of developing complications, comorbidities and severe forms of the disease. But Covid-19 can affect anyone, regardless of age or physical condition.
Studies, French and international, have shown that precariousness is also associated with an increased risk of infection and severe Covid. The work of the Île-de-France Regional Health Observatory (ORS) and Insee in particular highlighted as of April 2020 excess mortality in the poorest areas, particularly marked in Seine-Saint-Denis. Although no causal link has yet been clearly established, correlations with environmental, urban, social and healthcare system factors are possible.
In addition, certain factors associated with long Covid have been described, such as the initial severity or the number of symptoms present in the acute phase. However, healthy individuals can experience long Covid with symptoms such as fatigue, chest pain and headache, experienced months after recovery from acute infection.
The transmission of Sars-CoV-2 is largely related to “viral load”, the amount of virus present in the body of infected or sick people. It is generally either aerial (via droplets, aerosol) or by contact (direct or indirect).
Applying physical distancing measures therefore reduces the risk of transmission.
And since it is mainly airborne, regular ventilation of closed spaces (air renewal) and wearing a mask are also relevant to reduce the transmission of the virus. A recent review of the literature highlighted that long-distance transmission (> 2 m) of Sars-CoV-2 was possible in confined spaces such as restaurants, offices and was associated with inadequate ventilation of these spaces.
Wearing a mask is one of the key measures to reduce the spread of Sars-CoV-2 – and respiratory infections more broadly. Indeed, wearing a mask would reduce viral exposure if worn properly (mainly with regard to the FFP2 mask).
Several studies that examined its impact on the epidemic dynamics of Sars-CoV-2 had struggled to conclude that there was a significant effect on the spread of the virus… However, the authors moderated these results, in particular because of a large number of existing biases in the trials conducted and a relatively small number of people who followed the mask-wearing guidelines. This may have affected the results of the studies.
A literature review of 172 studies concluded that masks were effective in preventing the transmission of respiratory viruses (Sars-CoV-2, Sras or Mers).
The development of several effective vaccines against Sars-CoV-2 was a major breakthrough in 2020. Never before has a vaccination campaign started so quickly after the identification of a new pathogen.
Vaccination had a significant impact on the evolution of the pandemic by reducing viral load, incidence (number of new cases of a disease for a given period and population), hospitalizations and deaths – thus saving lives. tens of millions of lives worldwide. According to one study, vaccination would have prevented 15 million deaths between December 2020 and December 2021. These beneficial effects were mainly concentrated in high-income countries.
The rare cases of myocarditis (13 cases per 1 million doses) are mainly observed with mRNA vaccines (Pfizer, Moderna). While cases of thrombosis (10 cases per 1 million doses) are observed with adenovirus vaccines (AstraZeneca and Janssen). Vaccination remained effective against infection with the Omicron BA.4 and BA.5 subvariants, which still predominate to this day. The effectiveness of vaccination is highest in the first two months following the injection and then decreases by half beyond nine months.
Hybrid immunity, obtained after vaccination and natural infection with Sars-CoV-2, confers longer-lasting protection, as the infection can elicit a more diversified immune response.
After three years of a pandemic followed almost live, today we have a clearer view of its five points, ranging from the pathogenicity of the virus to the impact of vaccines.
Although the pandemic currently seems to be contained, it is still present as shown by the ever-fluctuating infection figures… Sars-CoV-2 therefore does not seem to be about to disappear and the future evolution of the epidemic remains unpredictable. Many questions remain, and therefore, much work remains to be done on the Covid.
*Nicolas Pulik, international development officer – ANRS| Emerging Infectious Diseases, Inserm; Armelle Pasquet-Cadre, infectious disease specialist – head of the crisis management unit, ANRS | Emerging infectious diseases, Inserm and Claveau Nathan, project manager, crisis response and scientific coordination, ANRS-MIE, Inserm
