In a study published on January 14 by Public Health England, researchers found that people infected by COVID-19 maintain an effective level of natural immunity for about five months. The researchers looked at antibodies made by people who were infected with COVID-19, and they collected samples over an extended period of time. The study has yet to go through the peer review process, but the researchers felt that the results were important enough to provide this update to healthcare professionals in light of the ongoing campaign to vaccinate susceptible individuals against COVID-19.

About the COVID-19 Immunity Study

Researchers found that a past infection with COVID-19 showed an 83% lower risk of getting infected again compared with a person who had never been infected. The researchers added that natural immunity was not absolute immunity. Some people did catch COVID-19 again. They also explained that it is unclear how long natural immunity lasts. The researchers surmise that people who have some immunity to the virus may still be able to carry the virus and spread it to others, even if their reinfection does not cause them to get sick a second time. People who have been infected twice can still carry the virus in their noses or throats. Their sneezes and coughs can transmit infectious viruses to others.

What the Researchers Have to Say About Natural Immunity

Susan Hopkins, who is the Public Health England Senior Medical Advisor, stated that they now understand that a person who has had COVID-19 develops antibodies and is mostly protected from reinfection. However, that protection isn't guaranteed, and they don't know how long it lasts. She added that even if a person knows they were infected, there is still a risk of reinfection. A second infection could allow a person to spread the germs to others. Severe illness from a second infection is less likely, explained Hopkins.

About the Study at Public Health England

The Public Health England research study was called SIREN. The researchers tested 21,000 public health and hospital workers across the United Kingdom beginning in June and lasting through November. Among the study participants, 6,614 tested positive for antibodies against the SARS CoV-2 virus, which is the virus that causes COVID-19 disease. About 14,000 of the study participants tested negative for antibodies. Of the 6,614 who had antibodies from their past COVID-19 infection, 44 of them developed a possible new infection. That showed an 83% level of protection against getting reinfected.

Ongoing Studies of Immunity Against the SARS CoV-2 Virus

Public Health England will continue its SIREN study. The agency will monitor healthcare workers for 12 months. The researchers want to determine if the natural immunity will last even longer. For now, the information collected by the researchers shows that people who got infected with SARS CoV-2 in the spring or summer months of 2020 could get reinfected now. The study will also look at the new variants and mutations of COVID-19 that have been shown to be more transmissible. They want to know if infection with the original strain or administration of the COVID-19 vaccine will confer lasting immunity to any of the variants of the virus.

Researchers Caution Against Letting Your Guard Down

Researchers caution against people letting their guard down. If somebody had COVID-19 in the spring or summer months of 2020, they can get reinfected. Even if they don't get severely sick, they could shed enough virus to transmit the infection to other people. Some people shed a lot of virus, and they could easily transmit infections to household members, coworkers or others with whom they are socializing. Hopkins pressed upon the importance of continuing to adhere to social distancing rules, wearing a mask and avoiding large gatherings of people.

Implications for Getting Through the Pandemic

The Public Health England study has important results that could facilitate a path out of the pandemic. On one hand, it's promising that reinfection with COVID-19 is rare at this time. Antibodies persist for at least five months, and they seem to do a good job during that time. However, there is concern about people being able to get reinfected and spread COVID-19 to others. This situation is potentially dangerous because a person who knows they were infected once might assume that they're not a threat to others. They might not follow public health guidance. The majority of the population will need to be vaccinated before all of the current public health restrictions can be removed.