The key to preventing secondary infection is in the nasal cavity! How long do nasal antibodies last after infection?

In recent days, various places have ushered in the first wave of infection peaks after liberalization, and the actual peak date of infection seems to be earlier than we expected, and the health threat of the new crown to the human body seems to be greater than predicted by experts
.
In the real world, the death group caused by the new crown is not limited to the elderly and those with underlying diseases, but is at risk
of severe disease and death at all ages.

In addition, it is more alarming that the antibodies produced after human infection are not once and for all, and there is a great possibility of repeated infection
.
The repeated infection of the new crown virus will bring trauma to the human immune system again and again, which poses a great threat
to human health.
In this case, we need to consider how long the antibodies produced after infection can remain in the human body? To what extent can the body be protected from secondary infection? Not only medical researchers are concerned, but also the general population
.

In order to answer these questions, researchers from Imperial College London and the University of Liverpool conducted a research analysis, they collected blood and nasal samples from 446 people infected with the new crown, including 569 plasma samples, of which 338 were collected from continuous time points, and 356 nasal samples, of which 143 were collected from continuous time points, respectively, measuring the effect of antibodies in the samples in neutralizing the original strain of the new coronavirus, the Delta variant, and the Omicron variant.
to analyze the duration
of effectiveness of antibodies in the body after infection or vaccination.

The research results, titled "SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination," were published in The Lancet's journal EBiomedicine
.

Studies have found that after 4 weeks of infection or vaccination, the nasal cavity of the human body begins to produce antibodies, but the level of antibody increase is limited, on average, the level of intranasal antibody immunoglobulin A (lgA) can last for 9 months, after which it begins to decline, which also means that the body's first line of defense against respiratory viruses begins to weaken.

Compared with antibodies in the nasal cavity, antibodies in the blood of infected people appeared 2 weeks after infection and increased 2181-fold after 9 months, and the period after that was higher than before infection, lasting at least one year
.

Figure 1 Research results (Source: [1])

The researchers analyzed the antibodies of 446 participants to understand how long antibodies in the nasal cavity and antibodies in the blood lasted, and also studied the effect
of the new crown vaccination on the body's nasal cavity and blood antibody levels.

Through sample collection and antibody level measurement, the researchers found that nasal and plasma lgG reactions lasted longer after infection with the new crown, while nasal lgA reactions lasted only 9 months
.
Of the 323 people vaccinated, 90% were vaccinated for the first time during the study follow-up, which resulted in an increase in antibodies in the nasal cavity and blood in the infected person, but the change in intranasal antibody levels was small and short-lasting
.
At the same time, the researchers said that the duration of intranasal antibodies was not affected
by the gender of the participants, the severity of the disease, and their age.

Fig.
2 Intranasal lgA and lgG reaction trajectories of new crown infected patients after the first vaccination (Source: [1])

In addition, the researchers found that even one year after infection, the antibodies in the participants' blood still had some protection against the body, but booster vaccination was needed to maintain it
.
And it should be pointed out that although the vaccine can effectively enhance the level of antibodies in the human blood, it does not significantly increase the level of
antibodies in the nasal cavity.
For this reason, it is crucial
to develop effective nasal spray or inhalation vaccines against the new coronavirus.

It is worth mentioning that after analysis, the researchers found that compared with the original strain, Delta variant and Omicron variant, the duration of antibodies produced by Omicron in the nasal cavity was the shortest, which once again provided a research basis
for repeated infection of Omicron.
And, after vaccination, the Omicron binding reaction did not reach levels
against both the Delta and the original strain.

In summary, studies have shown that the key to preventing secondary infection lies in the level of antibodies in the nasal cavity, which can only last for 9 months
after infection.
Future vaccines will require a significant increase in nasal lgA levels
if they want to completely prevent infection and transmission of the new coronavirus.
To date, intranasal and nebulized vaccines have shown great promise
in this regard.
Therefore, prioritizing the development of mucosal vaccines is crucial
.