Does a Covid infection protect against reinfection?

RIO DE JANEIRO, BRAZIL – Vaccines have high protective efficacy against infection or re-infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the 2019 coronavirus disease pandemic (Covid-19).

A new review available on the medRxiv * preprint server has shown that the protective effect of a previous infection with SARS-CoV-2 is at least equivalent to that of vaccination.

Does a Covid infection protect against reinfection?


Researchers performed a systematic review of all studies reporting reinfection with SARS-CoV-2. Immunity following natural infection has been demonstrated in various viral diseases. It is in fact responsible for the decline of most epidemics after a majority of susceptible hosts have been infected.

While early research indicated that SARS-CoV-2 induced potent immunity, its extent and magnitude remained to be characterized. Epidemiological results have indicated that HIV-positive individuals are unlikely to be re-infected.

In addition, HIV-negative individuals are protected against 80% of re-infections if they have already suffered an infection compared to previously uninfected individuals.

One study showed a risk of reinfection of 0.7% among 10,000 cases, while others found that 0.03% and 0.01% of people with a history of infection required hospitalization or had a fatal outcome , respectively.

Another interesting study has shown that being infected with the virus is at least as powerful a protective factor against re-infection as vaccination, looking at lab staff tested for infection daily.

The present study aimed to compare immunity rates in people with a history of infection versus those without immunity. This is important in the context of rising infection rates, even as vaccines are being rolled out.


Following a review of the literature that followed the PRISMA guidelines, the researchers found that the risk of reinfection was reduced by 90% compared to those who were naive to the virus. This protection was maintained for up to ten months.

The results corroborated previous studies which show how durable the level of protection conferred by previous infections is in preventing re-infection, similar to those who had been vaccinated.

Other researchers have found that humoral and cellular immunity remains active for ten months or even longer. These studies covered a range of countries with different age groups and regional coverage.

Despite the many differences in the included cohorts, the conclusion in all cases was that the risk of re-infection was very low after recovery from a previous infection or after vaccination.


Scientists concluded that the protective effect provided by a previous SARS-CoV-2 infection on re-infection is of the same protective effect as vaccination or even greater.

In the current pandemic conditions, it is essential to avoid strong outbreaks of infections to prevent the emergence of new variants that are potentially more transmissible and resistant to neutralization by antibodies directed against previous strains.

The first generation vaccines developed on several platforms have focused on the expression or introduction of the viral spike protein into the recipient’s body. The efficacy of these vaccines has been particularly high against symptomatic and serious illnesses and deaths following infection with SARS-CoV-2.

However, such protection is challenged by newer variants such as alpha, delta and beta strains.

The alpha and delta strains rapidly increased to become the dominant strains of the second wave and the following ones. Both are associated with significantly higher transmissibility, and the latter may also have partial immune escape capability, just like the beta variant. This has led to a possible reduction in vaccine effectiveness, although vaccines continue to reduce the number of symptomatic infections worldwide.

This study shows that a previous infection with or without seropositivity can provide immunity against reinfection with another viral variant. However, the researchers point out that the studies reviewed here may have suffered from multiple sources of bias.

The results correlate well with other serological studies showing that seropositivity was linked to a rate of reinfection lower than that of the rest of the population. It should be noted that the current review and serologic studies are based on the earlier period of the pandemic when the wild type or Wuhan strain was prevalent, and re-infections would have been largely caused by this variant.

At present, with competing strains that are more transmissible and able to evade antibody-mediated immunity, the reinfection profile may be different. Ultimately, more research needs to follow this study to characterize the protective effects against different strains of SARS-CoV-2.

*Important Notice
medRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.

Source: Medical News

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