When people reinfect with Covid-19, the odds of hospitalization or death are about 90% lower than a first-time Covid infection, according to a study published in The New England Journal of Medicine by Qatar researchers.
The survey indicates that there were few confirmed reinfections among 353,326 people who contracted Covid-19 in Qatar and that these cases were generally mild.
The first wave of infections in Qatar took place between March and June 2020. By the end of it, around 40% of the population had detectable antibodies against Covid-19. Afterwards, the country had two other waves, from January to May 2021. This was before the escalation of the more infectious delta variant.
To determine how many people reinfected, scientists at Weill Cornell Medicine-Qatar compared records of people with PCR-confirmed infections between February 2020 and April 2021. They excluded 87,547 people who had taken the vaccine.
The researchers found that, among the remaining cases, there were 1,304 reinfections. The average time between the first infection and reinfection was approximately nine months.
Among those with reinfections, there were only four cases severe enough to be hospitalized. There were no cases where people needed treatment in intensive care units. Among the cases of first infection, 28 were considered critical. There were no deaths among the reinfected group, while there were seven deaths among the first infections.
“When there are only 1,300 reinfections among that number of people and four cases of serious illness, that’s quite remarkable,” says John Alcorn, an expert in immunology and professor of pediatrics at the University of Pittsburgh, who is not associated with the research.
The study has limits as it was carried out in Qatar and it is unclear whether the virus would behave the same way elsewhere. The work was done when alpha and beta variants were the cause of many reinfections. The delta variant, which is now the predominant strain, was not mentioned in the research. This factor could have an impact on the number of reinfections.
Previous studies have shown that natural immunity reduces the risk of infection.
A study in Denmark and published in March indicates that most people who had had Covid-19 appeared to have protection against reinfection, which was stable for more than six months. But a check on the demographics of those who were re-infecting showed that they were mostly people aged 65 and over. This study does not clarify how long the protection lasts, nor does the Qatar study.
Alcorn’s own research into natural immunity shows that antibody levels also vary significantly from person to person. Scientists still don’t know what level of antibodies provides protection. But in some cases, post-infection levels may not be enough to prevent someone from reinfecting.
“It is necessary to determine whether protection against severe cases at the time of reinfection lasts longer, analogous to the immunity that develops against other seasonal ‘common cold’ coronaviruses. These elicit short-term immunity against mild reinfection and, in the long term, immunity against more severe cases with reinfection,” the study noted. “If that were the case for SARS-CoV-2, the virus (or at least the variants studied so far) could adopt a more benign pattern of infection when it becomes endemic.”
Don’t get wrong impressions about reinfection and vaccines
Dr Kami Kim, an infectious disease specialist who is not associated with this study, said care should be taken not to get the wrong impression that this means that people do not need to get vaccinated if they have already contracted Covid-19.
“It’s like asking if airbags and seat belts are needed,” said Kim, director of the Division of Infectious Diseases and International Medicine at the University of South Florida. “The fact that you have airbags doesn’t mean that seat belts won’t help you, and vice versa. It’s good to have the protection of both.”
Kim says it’s not worth the risk of getting the disease, particularly since an infection could bring the long-term effects with it. “The incidence of prolonged Covid is much greater than the risk of getting a vaccine,” says Kim.
Furthermore, vaccines not only prevent someone from getting sick, they also protect the community.
“Modern medicine is much better. People get cancer and they survive, they get autoimmune diseases and they thrive. It is not always possible to know who is vulnerable to more serious illnesses. And literally, you could be putting people you care about at risk if you get sick and expose them,” says Kim. “Without vaccination, you can’t go back to having a normal life.”
Vaccines to limit the possibility of variants
Limiting the number of diseases also limits the possibility that more variants will develop—variants that may even be more dangerous than those that are in circulation now.
Alcorn says there is another important lesson from this study.
“Vaccines continue to be our best method to get to the same place these people who have been infected are located,” says Alcorn. “The main conclusion of this study is that there is hope that, through vaccination and recovery from infections, we will reach the level where everyone has some level of protection.”
Reference: CNN Brasil