Lancet: Nasal mucosal immunity is a key factor in the protection of the new crown

As the main variant of the novel coronavirus (SARS-CoV-2), Omicron can significantly reduce the neutralization efficacy of different epitope neutralizing antibodies, and has strong immune escape characteristics, so there is still the possibility
of breakthrough infection after "Yangkang".
How long the antibodies produced after infection can be effective, and whether there are other ways to effectively reduce the risk of secondary infection, need to be thoroughly studied
.

A study 1 found published in LANCET INFECT DIS titled "Transmission of COVID-19 in 282 clusters in Catalonia, Spain: a cohort study.
" : Increased viral load values in nasopharyngeal swabs in COVID-19 patients were associated with a greater risk of transmission of positive SARS-CoV-2 PCR tests between contacts, and higher viral load in swabs of asymptomatic contacts was associated with a higher risk of developing symptomatic COVID-19, suggesting that viral load may be the main driver of transmission; Moreover, the incubation period of asymptomatic contacts is shorter than that of contacts with low viral load, indicating that nasal viral load is high, the risk of SARS-CoV-2 transmission is high (Figure 1), and the incubation period is shorter, indicating that the level of nasal viral load is closely related to the severity of COVID-19 symptoms and transmissibility, further suggesting that reducing nasal viral load has an important role
in the prevention and treatment of new coronavirus.

Figure 1 PROBABILITY OF SYMPTOMATIC ILLNESS CAUSED BY VIRAL LOAD (SOURCE: LANCET INFECT DIS)

The nasopharynx is the first site where the new coronavirus invades the human body, and the nasal antibody IgA produced by mucosal immunity is the most abundant mucosal antibody, which plays an important role
in effectively neutralizing the upper respiratory tract virus.
To reduce the risk of transmission, reduce SARS-CoV-2 infection, and reduce nasal viral load, this can be achieved by increasing nasal IgA antibodies
.
However, there are few studies on the long-term persistence of nasal antibodies, and the results are mixed, showing that nasal antibodies may persist for 3 to 9 months, and passive penetration of plasma antibodies into the mucosa may not provide persistent viral immunity
.
Therefore, understanding whether post-COVID-19 immunization can evoke a nasal IgA response is particularly important
for developing vaccines to prevent infection and transmission and finding effective ways to enhance mucosal immunity.

A study published in The Lancet eBioMedicine titled "SARS-CoV-2-specific nasal IgA wanes 9 months after hospitalisation with COVID-19 and is not induced by subsequent vaccination"² Findings: After COVID-19 infection or vaccination, the body's blood and nasal passages produce high concentrations of antibodies that enhance the response to the original strain, Delta, and Omicron variants
.
However, for Omicron, the nasal IgA response is particularly short-lived
.
This may be an important reason why
the new coronavirus can repeatedly infect the human body.

In this follow-up study, the research team prospectively collected plasma and nasal samples
from 446 adults hospitalized with COVID-19 between February 2020 and March 2021.
The neutralization response
of antibodies to the original strain, Delta, and Omicron (BA.
1) variants was evaluated by measuring the antibodies in the participants' nose/plasma, as well as the duration of the antibodies.

Note: * = p < 0.
05, ** = p < 0.
01, *** = p < 0.
001, **** = p < 0.
0001.

Figure 2 Nasal and plasma antibody reactions 12 months after new crown infection (Source: eBioMedicine)