The Sars-CoV2 virus circulates relentlessly and many of us are infected despite a full vaccination course or a past recovery. How common are reinfections? Are reinfections with Sars-CoV2 dangerous?
Sars-CoV2 belongs to the Coronavirus family, a family to which the terrible Sars1 and Mers viruses but also the ‘simple’ cold viruses such as OC43 and 229E belong. Coronaviruses are characterized by the ability to reinfect their hosts. Think of the common cold that can infect us up to 4 times a year. The ability to re-infect derives from the fact that coronaviruses mutate and therefore are able to evade the antibodies produced by the hosts following infections, moreover the antibodies themselves decay a few months after infection. Now that we have established that coronavirus reinfections are the norm, we can ask ourselves how common are they with Covid19?
Omicron, coronaviruses and reinfections
The phenomenon of reinfections at the beginning of the pandemic was quite rare: partly due to a lower viral circulation and partly due to the mechanisms described. Today, with the arrival of Omicron, reinfections are a very common phenomenon, it is estimated that in the United Kingdom it has gone from a risk of re-infection of 10 per 100,000 to a risk of 180, therefore an increase in risk of about 16 times.
Many reinfections are submerged
The Omicron variant has made reinfections even more common due to its ability to evade the immune system and its many mutations. It should also be considered that many reinfections can be ‘submerged’ as the Omicron variant is characterized by a high percentage of asymptomatic, so many people may have reinfected without even realizing it.
More and more mild re-infections
We have established that reinfections are the norm in coronaviruses and have become very frequent with Omicron, but are they dangerous? Do reinfections increase the risk of serious illness and death? Generally reinfections are milder from time to time, this is because each infection generates an immune response that reminds our immune system of the virus. Overall, the data indicate that recovery from the disease reduces the risk of hospitalization and death.
The ‘submerged’ cases
If reinfections were worse from time to time in terms of symptoms we would see hospitalizations and deaths rise as infections rise but fortunately this has not been happening for months (obviously hospitalizations and deaths rise as infections rise, but compared to 2020 in a way much less marked).
This phenomenon should not surprise us because we have learned that our immune system is strengthened following stimuli from the same pathogen and therefore in most cases healing guarantees a milder disease.
Some viral diseases such as Dengue do not respond to this rule, in fact, subjects cured of Dengue can experience a more severe disease in case of reinfection as the phenomenon of ADE occurs, i.e. an enhancement of the disease mediated by the antibodies themselves. ADE is an extremely rare phenomenon, which fortunately does not concern Sars-CoV2.
What are the risks
An American pre-print study released a few weeks ago (still pending review) studied reinfections in a large group of people. The American study shows that the accumulation of infections also increases the risks associated with them: this does not mean that the second infection will be more serious than the first but it means that the risks of the first are associated with the second and so on.
Sample too specific
These results, however, must be contextualized: the starting sample derives from a particular group of people, the American veterans, characterized by an average age of 65 years, mainly male and very high body mass index, therefore obese. We know that age, gender and weight are three important co-factors for the severity of Covid19, so it is difficult to extend the results of the American study to the general population.
Reinfections from a public health point of view
We have analyzed reinfections from a biological and immune point of view, we have said that they are a common phenomenon with Coronaviruses and that in most cases they are milder as the immune response is strengthened.
However, if we analyze the phenomenon from the point of view of public health, reflections are necessary.
- Reinfections from Covid19 tend to be mild but this is not valid for the whole population, there are in fact groups very subject to serious disease. Fragile individuals may experience severe disease even if they are reinfected.
- The risk of Long Covid is not yet fully understood, we do not know which subjects are at risk and if reinfections can increase this risk. Finally, we know that the Long Covid risk is reduced by vaccinations but we have no data on healings and their potential protective role.
- The risks and effects associated with each reinfection add up.
These reflections on public health must lead us to avoid reinfection in any way since every time we come into contact with the virus we run the risk of running into severe illness or long-term consequences.
TAKE HOME MESSAGE
- Reinfections are very common in Coronaviruses
- Reinfections are caused by the high number of virus mutations and the decay of antibodies
- Reinfections with Covid19 tend to be milder
- The population is very heterogeneous and the response to the virus also therefore reinfections must be avoided
REF:
https://www.gavi.org/vaccineswork/covid-reinfections-are-they-milder-and-do-they-strengthen-immunity
https://www.theguardian.com/world/2022/jun/22/uk-worried-rising-covid-infections
https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveycharacteristicsofpeopletestingpositiveforcovid19uk/2february2022#reinfections-with-covid-19-uk
https://www.cdc.gov/features/rhinoviruses/index.html
https://www.nature.com/scitable/content/model-of-antibody-dependent-enhancement-of-dengue-22403433/
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)00462-7/fulltext
https://www.nejm.org/doi/10.1056/NEJMoa2119658
https://www.nejm.org/doi/full/10.1056/nejmc2108120
https://www.thelancet.com/journals/lansea/article/PIIS2772-3682(22)00028-2/fulltext
https://academic.oup.com/cid/article/73/10/1882/6170939?login=false
https://assets.researchsquare.com/files/rs-1749502/v1/499445df-ebaf-4ab3-b30f-3028dff81fca.pdf?c=1655499468
Aureliano Stingi, doctor in molecular biology, works in the field of precision oncology. He collaborates with the World Health Organization in the battle against Covid19-themed fake news
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