How much immunity do we get from COVID infection? Large study provides new clues

After being infected with COVID, whether it’s the first, second, or third time, many of us wonder how protected we are from re-infection and whether we might be infected with new variants. increase. And if I get COVID again, will the immunity gained from this infection reduce the severity of the next one?

a new research To answer these questions, published in The Lancet, we examined the strength and duration of innate immunity by COVID variants.

The authors collected data from 65 studies in 19 countries, making it the largest review to date on this topic. These studies compared her COVID risk in previously infected people with those who were not previously infected. Studies examining innate immunity (hybrid immunity) combined with vaccination were excluded.

The researchers aimed to assess whether infection elicits similar protection against reinfection with different subspecies and whether this weakens in different ways over time.

The analysis spanned studies from the beginning of the pandemic to September 2022 and focused primarily on alpha, beta, delta and omicron BA.1 variants.

Protection from reinfection

The authors independently assessed protection against reinfection, symptomatic disease, and critical illness (defined as hospitalization or death).

Previous infections were highly protected against reinfection with alpha, beta and delta variants, but less so against Omicron BA.1. Previous infections provided moderate protection (45%) from reinfection with omicron BA.1, compared with stronger protection (82%) against pleomicron variants. This was also the case for symptomatic infections.

Data from a long-term study showed that protection against reinfection with the pleomicron variant declined to 78.6% at 40 weeks, but declined rapidly to 36.1% with omicron BA.1.

However, when assessing severe disease, all variants showed sustained protection of over 88% over 40 weeks. This is not to say that protection will drop significantly after his 40 weeks. Rather, the available data that track people long enough to allow the authors to draw strong conclusions beyond this time frame appear to be limited.

The results also revealed that protection against severe disease after natural infection was comparable to that obtained from two vaccination doses for both pleomicron and omicron BA.1 variants.

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Understanding our findings

Years are a long time for a highly contagious respiratory virus, and SARS-CoV-2 (the virus that causes COVID) is no exception. It has generated a worrying array of subspecies due to its enhanced transmissibility and ability to evade immune responses compared to ancestral viruses.

The observations of studies that treat protection against pleomicron variants and omicron BA.1 separately make some sense. Omicron variants are different from their predecessors.

By way of background, neutralizing antibodies generated after previous viral infection are important to prevent subsequent viral entry into susceptible cells. These Y-shaped molecules recognize and bind intact proteins on the outside of the virus, preventing the virus from catching on cellular receptors necessary for infection.

However, in order to persist, viruses like SARS-CoV-2 aim to introduce random mutations into the genome during replication and continuously modify proteins to escape immune recognition.

Because the Omicron lineage has enough mutations to virtually distinguish it from previous variants, Avoids existing antibodiesEvasion from neutralizing antibodies explains the inability to control reinfection with omicron variants.

Thankfully, we don’t rely solely on antibodies for protection.a type of immune cell called T cells It recognizes fragments of viral proteins rather than intact proteins. This means that many more mutations are needed in the viral genome to fully evade T-cell immunity.

Unlike antibodies, T cells do not search for viruses. Instead, it recognizes infected cells and eliminates them quickly to reduce viral factories in the body. Thus, after infection, T cells activate where neutralizing antibodies may not have worked. A strong T-cell response to coronavirus is essential to prevent severe disease, and fortunately, it is more difficult for Omicron to circumvent.

SARS-CoV-2-specific T cells fade more slowly than antibodies.In fact, people infected with the similar coronavirus SARS in 2003 still had T cells Recognize SARS-CoV-2 17 years after infection.

Infectious disease and vaccination

Natural infection may offer protection equivalent to vaccination, but this doesn’t mean you should try to get infected.SARS-CoV-2 remains dangerous and unpredictable. It is a virus and in some cases can cause many harmful effects that linger long after recovery.

The authors suggest that an individual’s prior infection status and timing should be considered, along with booster vaccination, to predict prevention. However, this may be difficult to implement due to reduced surveillance in most countries compared to the early days of the pandemic. in any case, COVID certificate It is not used much now.

They also suggest that their findings could be used to inform optimal timing for booster vaccination strategies. .

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The authors acknowledge that there are not many studies on natural infection compared to post-vaccination protection, so further high-quality long-term follow-up studies are important to complement these findings. will be There have also been few studies mapping protection against the newer omicron sublineages. As the pandemic continues, we have much to learn about immune protection against this evolving virus.