T cell immune responses seen a year after infection

Strong and sustained T-cell responses were seen even when people were not re-infected or vaccinated

Strong and sustained T-cell responses were seen even when people were not re-infected or vaccinated

As in most countries where the Omicron variant had become dominant and caused a high spike in daily cases, the third wave in India, propelled by Omicron, caused a large number of reinfections in unvaccinated people and breakthrough infections, even in fully vaccinated people. Around the world, however, the Omicron variant was found to cause only mild illness in fully vaccinated people and those with a previous infection. This was real evidence that prior infection and/or full vaccination with two doses protects against progression of the disease to a severe form.

Protective effect

Laboratory studies conducted in all countries have only studied the neutralizing capacity of sera from people who have recovered from COVID-19 and people who have been fully vaccinated. This could only shed light on the ability of previous infection and/or vaccination to prevent infection by highly permeable immune escape variants. But no studies have been done to evaluate the protective effect of memory T cell immune responses against serious diseases 12 months after the primary infection. A new study from Wuhan addresses this gap. The results have been published in the journal The lancet microbe

Regardless of severity

The researchers found that neutralizing antibodies were detectable in “most individuals” even 12 months after infection, and it remained stable for 6-12 months after the initial infection in people younger than 60. The researchers found that “multifunctional T cell responses were detected for all SARS-CoV-2 viral proteins tested”.

Most importantly, the magnitude of the T-cell responses showed no difference, no matter how severe the disease was. While the ability of antibodies to neutralize was almost absent against the Beta variant, it was reduced in the case of the Delta variant.

In contrast, the T cell immune responses were detectable in all 141 subjects tested 12 months after infection and even when they had lost the neutralizing antibody response. And the T-cell responses responded to the beta variant in most of the 141 individuals.

Neutralizing Antibodies

“SARS-CoV-2 specific neutralizing antibody and T cell responses were maintained 12 months after initial infection. Neutralizing antibodies to the D614G, Beta and Delta were reduced compared to those for the parent strain, and were generally reduced. Memory T-cell responses to the original strain were not disrupted by new variants,” they write. “Our findings demonstrate that robust antibody and T-cell immunity to SARS-CoV-2 is present in most recovered patients 12 months after moderate to critical infection.”

T-cell robustness

The study reveals the durability and robustness of the T cell responses to variants, including Delta, even after one year of infection. Most importantly, the robust and long-lasting T cell responses were seen in people who have not been reinfected or vaccinated. This would mean that even without vaccination, a person infected with the virus even a year ago would have a robust immune response, protecting against disease progressing to a severe form requiring hospitalization. But the neutralizing antibodies were found to wane at the end of 12 months.

One may recall that, except for the Oxford vaccine (AstraZeneca), none of the studies evaluated the vaccines’ ability to prevent infection. The end point of all vaccine efficacy studies was to evaluate whether vaccinated people developed symptomatic disease or not.

Lack of studies

However, the booster doses aggressively pushed by vaccine manufacturers are intended to prevent infection. And even when the neutralizing antibodies increase after a booster injection, they drop after a few months. No studies have been done to assess whether booster doses improve the immune response of T cells, which is the main criterion for vaccination.

In the case of neutralizing antibodies, the researchers found that 121 (85.8%) were positive for neutralizing antibodies at 6 months, while there was a slight decrease at the end of 12 months, as only 115 (81.6%) were positive. were for neutralizing antibodies.

The neutralizing antibody titers showed no difference based on disease severity – mild or moderate – or in subjects younger than 60 years of age. However, neutralizing antibody titers decreased in older people and those with critical illness.

Reaction to strains

One year after infection, 115 of 141 (82%) individuals had neutralizing antibodies to the parent strain from Wuhan, China. “In contrast, only 68 (48%) had neutralizing antibodies to D614G, 32 (23%) had neutralizing antibodies to the Beta variant, and 69 (49%) had neutralizing antibodies to the Delta variant,” they write.

SOURCE – www.thehindu.com

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