Hyderabad : If it wasn’t bad enough being infected once with COVID-19, now there is a talk about getting reinfected by this dangerous virus. Since August 2020, there have been anecdotal cases of people getting reinfected with the COVID-19 virus. There have been reports from Hong Kong, Belgium, the Netherlands, the US, and closer home, from Bengaluru, Mumbai, and even Hyderabad. These are all isolated cases but they have sent the world in a tizzy. The 28 million dollar question on everyone’s lips is: “Is reinfection a myth or a reality?” Before trying to answer this question, let us look at the logical and scientific aspects of reinfection.

What does reinfection mean?

A person is considered to be reinfected with the virus when:

• Step 1 – He/she got infected in the past.

• Step 2 – Got over it completely.

• Step 3 – Was virus-free for a period of time

• Step 4 – Developed a fresh infection with a different strain of the virus.

This sounds like a simple sequence of events but there are many pitfalls at each step. The major pitfalls are that the RT-PCR test; though considered the gold standard; is not 100 percent accurate. There are a significant number of false positives (where the person is actually negative for the virus but the test falsely reads him as positive) and false negatives (where the person is actually positive for the virus but the test falsely reads him as negative). Also, very few centers are equipped to test the exact strain of the virus.

In all the anecdotal reports so far, only the Hong Kong patient met all the criteria to confirm reinfection. Even in his case, there was no definite proof that it wasn’t a lab contaminant or a lab error!

What are the body’s mechanisms to prevent reinfection?

Once a person gets infected, they produce antibodies that fight the infection and protect them from new infections. These antibodies are produced after 2 – 6 weeks but unfortunately start reducing after 12 weeks and often disappear after 16 weeks. This makes the person vulnerable to reinfection after 16 weeks. Some patients, especially those with milder infections, produce very few antibodies after the first infection. This makes them vulnerable to reinfection even before 16 weeks.

Is reinfection more dangerous than the primary infection?

Luckily, we all have an immunological memory, which never forgets the virus. As soon as the virus enters the body the second time, the immune cells remember and recognize it and mount a strong response. This limits the intensity of the infection the second time around. Hence reinfections are usually milder than the initial infections. Some reinfections may also be asymptomatic.

If reinfection is so mild, why should we worry about it?

Once a person gets the infection, it does not mean he is safe and has an “immunity passport” and can roam around wherever he pleases without taking adequate precautions. If the first infection is very mild, he may not have an adequate antibody supply and might get a more severe infection the second time. This is especially true if the viral load he is exposed to is high. Also, persons who are reinfected can transmit the virus to other people. This is what we should worry about.

Theoretically, reinfection is very much possible as the antibodies wane over time and the virus gets smarter at evading the immune system by mutating (changing its appearance). Fortunately, among the 28 million COVID-19 cases that have been reported worldwide, very few cases of reinfection have been documented. Even accounting for errors of reporting or limitations of testing, this translates to a minuscule percentage of reinfection. Considering the low numbers and low intensity, at this point in time, reinfection is not something we should be worried about. Our focus should be on preventing primary infections by practicing SMS (Social distancing, Mask, and Sanitization).

Dr Andrews is a Nephrologist at Apollo Hospital, Hyderabad.

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