Can the new coronavirus be infected twice?

Nowadays, with the adjustment of epidemic prevention policies, many people have begun to worry about what to do if they are infected.

At the same time, there is a saying circulating among the people: since so many people have been infected, the sooner you get tested, the better, which is equivalent to getting a vaccination.

Whether this statement is true or not actually depends on whether the new coronavirus can infect people twice or more. So is it true?

If you get COVID-19 once, will you get it again?

Let me give you the answer first: Yes.

The highest number of COVID-19 infections we found in the news is five. In many countries, it is not uncommon to be infected twice or even three times.

A recent study in the journal Nature shows that globally, 2.5 cases of reinfection with the coronavirus occur per 100 people exposed to the virus each year. Although the probability is not high, it is not zero.

Related research also found several rules:

People who have been vaccinated have a lower risk of reinfection

People who were asymptomatic during their first infection are more likely to become infected again and develop symptoms

Children and the elderly are more susceptible to repeated infections

Some infectious diseases, such as measles, rubella, mumps, hepatitis A, etc., are not easily reoccurring after one infection. These pathogenic microorganisms are like "natural vaccines". When they invade again, the body will use the previously formed immune mechanism to protect itself.

Some infectious diseases do not have similar characteristics, such as influenza. Because there are many types of viruses and they mutate quickly, they can easily "escape" from the human immune system. This makes influenza not only easy to be infected repeatedly, but also requires vaccination once a year.

The new coronavirus belongs to the latter category, and one infection does not provide lifelong immunity.

Omicron, more likely to be infected twice

Different strains of the same novel coronavirus have different abilities to cause multiple infections:

Delta and previous variants are less likely to cause reinfection, but Omicron is more likely.

From 2020 to the end of last year, the original strain of the new coronavirus, as well as its various variants from Alpha to Delta, did not have strong immune escape capabilities and were therefore not easily reinfected.

However, since this year, the Omicron variant that has become the main one has a strong ability to cause reinfection. Regardless of whether you have been infected with Alpha, Delta or Omicron before, the risk of being infected with Omicron again is higher.

Data from the UK show that from July 2020 to early January 2022, the number of reinfections per 100,000 people-days was 20.8. The median time for these people to be reinfected was 10 months.

However, the risk of reinfection caused by the Omicron strain is 4.38 to 6.63 times that of the Delta strain.

As of February this year, the UK has reported 650,000 cases of COVID-19 reinfection, most of which occurred after Omicron became the dominant virus in November last year.

Image source: Reference [1] Chinese translation: Ding Xiang Doctor

At the same time, previous infections provide less and less protection against new virus variants, and the time interval between reinfections becomes shorter and shorter.

For other strains, previous infection provided 85% protection against reinfection within 6 months; but for Omicron, this protection dropped to only 19%.

Earlier this year, a 31-year-old Spanish woman was infected with the coronavirus twice in 20 days, one was Delta (asymptomatic) and the other was Omicron, setting a new record for the "shortest time interval."

The good news is

Reinfection symptoms are generally milder

The "natural vaccine" property of Omicron is not strong, and the protective effect of "Yang" once against "Yang" twice is not strong either.

The figure below shows the COVID-19 infection data in Portugal as of September this year. Studies have shown that a large number of people infected with Omicron BA.1 and BA.2 were infected with BA.5 three months later, and the protective effect between them was very low.

Image source: Reference [2]

However, overall, for those who are reinfected, their symptoms are generally milder.

A study published in late 2021 investigated 1,304 cases of reinfection in Qatar, when the prevalent strain was still the Delta strain.

The good news is that, probably because the immune system has been activated after the initial infection, the overall symptoms and danger levels of these reinfected people have become lower, and the chances of hospitalization or death are 90% lower than the initial infection. No one was hospitalized in the intensive care unit, and no one ended up dying.

Image source: Reference [3]

Studies have found that the chance of developing severe disease in reinfection is only 0.12 times that of the initial infection. Recent studies on the mainstream strain Omicron have also found that reinfection generally has milder symptoms. As of February this year, studies among Indian medical staff showed that the probability of moderate or above symptoms in reinfection was much lower than that of the initial infection.

However, although the symptoms of reinfection are generally milder, a small number of people will suffer from more serious other diseases during repeated infections. In November this year, a US study using data from more than five million people showed that within six months of reinfection, the risk of additional death due to COVID-19 and other diseases increased by nearly one-fold.

More rules about reinfection with the new coronavirus require further scientific exploration.

Preventing COVID-19 Infection

We still need to be prepared

Being infected with the new coronavirus once and recovering does not mean that "everything is fine."

Because there is a possibility of repeated infection, and there is still a certain risk of developing severe illness, and infecting high-risk groups such as the elderly and patients at home.

Although the overall symptoms of reinfection are alleviated, the existing symptoms are still very uncomfortable for many people. After all, no one wants to catch a cold again and again. Not to mention that for the elderly and those with underlying diseases, reinfection is somewhat dangerous and will affect their normal life.

Therefore, even if you have been infected before, you still need to take precautions and try your best to protect yourself and those around you from infection later or less.

For people who have been infected, getting vaccinated, washing hands frequently, and wearing masks are still good ways to protect yourself and the weak around you, such as the elderly, the sick, and children.

It is worth mentioning that it is also necessary to get vaccinated after infection. Its benefits even go beyond this. Studies have found that vaccination can also reduce the incidence of hospitalization and death.

A cohort study published in JAMA this year found that people who had been infected before and completed primary vaccination after a negative test could still reduce the risk of reinfection by about half. Similarly, the chance of reinfection in unvaccinated people was about 2 times higher than that of fully vaccinated people.

Especially when the possibility of reinfection with Omicron becomes higher, even if we have tested positive, it does not mean we will not be infected again. Don't take it lightly and don't accidentally become "Chongyang Zhenren" again.

Image source: Internet

References

[1]Mallapaty S. COVID reinfections surge during Omicron onslaught[J]. Nature, 2022.

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[3]Abu-Raddad, LJ, Chemaitelly, H., & Bertollini, R. (2021). Severity of SARS-CoV-2 reinfections as compared with primary infections. New England Journal of Medicine, 385(26), 2487-2489.

[4]Sacco, C., Petrone, D., Del Manso, M., Mateo-Urdiales, A., Fabiani, M., Bressi, M., ... & Riccardo, F. (2022). Risk and protective factors for SARS-CoV-2 reinfections, surveillance data, Italy, August 2021 to March 2022. Eurosurveillance, 27(20), 2200372.

[5]Klein N P. Added Benefit of Covid-19 Vaccination after Previous Infection[J]. New England Journal of Medicine, 2022, 386(13): 1278-1279.

[6]https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/articles/coronaviruscovid19latestinsights/infections#reinfections

[7]Deng L, Li P, Zhang X, et al. Risk of SARS-CoV-2 reinfection: a systematic review and meta-analysis[J]. Scientific reports, 2022, 12(1): 1-9.

[8]Why have I caught Covid five times? https://www.telegraph.co.uk/health-fitness/body/have-caught-covid-five-times/

[9]https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveycharacteristicsofpeopletestingpositiveforcovid19uk/19january2022#reinfections-with-covid-19-uk

[10]Ferguson N, Ghani A, Cori A, et al. Report 49: Growth, population distribution and immune escape of Omicron in England[J]. Imperial College London, 2021, 10. https://www.imperial.ac.uk/media/imperial-college/medicine/mrc-gida/2021-12-16-COVID19-Report-49.pdf

[11]Covid: Woman caught virus twice within record 20 days https://www.bbc.com/news/health-61161529

[12]Reynolds CJ, Pade C, Gibbons JM, et al. Immune boosting by B. 1.1. 529 (Omicron) depends on previous SARS-CoV-2 exposure[J]. Science, 2022, 377(6603): eabq1841.

[13]Morris, CP, Eldesouki, RE, Fall, A., Gaston, DC, Norton, JM, Gallagher, ND, ... & Mostafa, HH (2022). SARS-CoV-2 reinfections during the Delta and Omicron waves. JCI insight, 7(20).

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[15]Cavanaugh AM, Spicer KB, Thoroughman D, Glick C, Winter K. Reduced risk of reinfection with SARS-CoV-2 After COVID-19 vaccination—Kentucky, May-June 2021. MMWR Morb Mortal Wkly Rep. 2021;70(32):1081-1083. doi:http://dx.doi.org/10.15585/mmwr.mm7032e1

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