Becoming reinfected with the coronavirus depends on the amount of neutralizing antibodies that the person in question has. If they are few in number, there is a much higher possibility of reinfection. In order to address this issue, science always looks at the available data, and the evidence at hand is always from the past. For now, there is still little data about the omicron strain. But the step from the previously dominant variant, delta, to this latest, more-contagious version of the virus can help us to understand it.
Omicron is infecting us more because it is able to evade the immunity that we may have had, be it via vaccination or previous infection with other variants. As such, it is possible for a person who has had omicron to become infected once more with the same strain, or the possible variants that could emerge in the future. All of this will depend on the number of neutralizing antibodies that a person has.
The only option for knowing if a person is at risk of reinfection would be to know if they have a sufficient amount of these antibodies, but this kind of test is very complex and is only done in the context of research projects. What’s more, they have to be done on a regular basis.
Just after an infection is when we have the highest level of neutralizing antibodies, although there are infected people who do not end up producing these specific antibodies in great quantity. As time passes after the infection and the activation of an immune response falls, we begin to have a higher risk of reinfection because the amount of neutralizing antibodies is also decreasing. That is why people with infections should also get vaccinated some time after having had the illness.
Data supplied this summer by the United States’ Centers for Disease Control and Prevention (CDC) indicate that among people who have had a SARS-CoV-2 infection, the vaccination provides additional protection against reinfection.
It is possible for a person who has had omicron to become infected once more with the same strain, or the possible variants that could emerge in the future
The same happens with vaccinated people who have not been infected, as with time their neutralizing antibodies also fade. This is why booster shots are being used to increase the amount of these antibodies and to reduce the risk of infection. Also, the probabilities of reinfection could increase if a new variant of the virus were to appear that can evade the immunity generated by omicron, previous variants or the vaccines that we have at the current time.
There are many reported cases of people who have been reinfected with SARS-CoV-2. This is easier to demonstrate from a scientific point of view when people are infected with different variants. That’s because it allows for the distinction of a reinfection, compared to a situation whereby the virus has remained hidden in the organism and has reappeared after a certain time has passed – this is something that can happen with people whose immune systems are compromised.
As we have seen in recent weeks, the appearance of omicron has greatly increased the risk of reinfection. Report 49 from the Centre for Global Infectious Disease Analysis in the United Kingdom states that it is associated with an increase in the risk of reinfection of between 4.8 and six times that of the delta variant.
This rise is related to the potential of this variant to evade the previous immunity from a natural infection with other variants and also from vaccines. In order to stop the entry of omicron in cells, we know that higher quantities of neutralizing antibodies are needed. This is one of the reasons why clinical studies have begun with vaccines that are specifically designed for omicron. However, we cannot rule out in the future that other variants, which are more transmissible than omicron and evade immunity, also emerge. This is why monitoring for new variants is important.
While the possibility of reinfection is real, it should be noted that the risk of hospitalization or the development of serious illness drastically falls from the moment we get over a natural infection or we are fully vaccinated.
Cellular and humoral immunity against the virus are proving to be key to preventing hospitalizations and deaths, independently of the variant that we are infected with. That is why it is so important that vaccines are available to the whole world. While vaccinations cannot completely stop the advance of new infections or reinfections, they can avoid the deaths of people infected on a global scale.
Nuria Izquierdo-Useros is a doctor of biology, and the head of the emerging pathogens group at the IrsiCaixa research institute.
Question sent via mail by Paula García.
Coordination and editing: Victoria Toro.
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