You almost certainly know someone who has had Covid-19  more than once. Still, in the realm of speculation, the second infection of a known individual may have occurred in the previous few months, when the Omicron variant (BA.1) or subvariant BA.2 swept the globe. Unfortunately, the situation is typical, and new reinfections are becoming increasingly common.

To explain the issue of Covid-19 reinfections, it is necessary to reflect on the following three issues: the body’s immunity against disease does not always last forever; the virus is constantly mutating, and booster doses of vaccines are still needed.

Limited body immunity

“The coronavirus almost always enters the human body via the nose and throat. Immunity in the mucosal linings of these areas tends to be relatively short lived compared to systemic immunity throughout the body. This may explain why protection against severe illness, usually rooted in the lungs, lasts longer than protection against infection,” says Paul Hunter, consultant to the World Health Organization (WHO) and professor of medicine at the University of East Anglia, UK, in an article for The Conversation website.

For Hunter, the shorter duration of mucosal immunity “may explain why protection against severe illness, usually rooted in the lungs, lasts longer than protection against infection.”

Therefore, some studies try to make a vaccine available that is applied as a nasal spray. To be more specific, researchers at the University of Hong Kong are testing a formula that immunizes against covid and the flu (influenza). Tests have already been done on an animal model.

Omicron mutations

In addition to the loss of potency of previously acquired immunity, a factor that increases the risk of reinfection is mutations in the virus. When some structure is modified, eventually, the body’s antibodies may have greater difficulty in identifying the infectious agent. In addition, the mutation can be positive and make the virus more transmissible, as happened with the Ômicron variant.

Both the original Omicron (BA.1) and the subvariant BA.2 are known as the two most transmissible strains, so far discovered, of the covid-19 virus. In comparison, BA.2 did even better than the other when it came to invading healthy cells, according to the World Health Organization. 

Initial data suggest that BA.2 seems inherently more transmissible than BA.1, he points out.

Reinfection of the new variant

Obtaining data on the number of Covid-19 reinfections is not easy.

A British survey points out that, until February 6, 2022, the local health system accounted for more than 14.5 million primary infections and about 620,000 reinfections in England alone. From these data, it is possible to estimate that one reinfection occurs for every 24 primary infections. The curious thing about the data is that more than 50% of all reinfections were counted from December 2021, when the Omicron variant was already established in the country.

In parallel, a study by Imperial College London found that Omicron is 5.4 times more likely to cause reinfection. Because of this evidence, there is a consensus that mutations in the Spike (S) protein of the new variant facilitate new cases.

Reinforcement of vaccines

A third factor that must be added to the equation that explains the reinfections of covid-19 is the natural reduction in the effectiveness of vaccines over the months. Because of this, health authorities around the world recommend booster doses and, more recently, the fourth dose of the vaccine begins to be released.

In the United States, the new booster is recommended for everyone over the age of 50.

“Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals,” Peter Marks explained Tuesday in a statement. Marks is director of the Center for Assessment and Biological Research from another US health agency, the Food and Drug Administration (FDA).

Given this evidence, it is possible to believe that, in the coming years, people should receive annual reinforcements against covid-19, as with flu shots. The question is whether the formulas will be adapted annually or will they remain the same. Possibly, they will consider the strains with the greatest circulation and help the human species to live with this virus more.

Image Credit: Getty

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