How common is Covid-19 reinfection?

Asked by Anonymous 

Stokel-Walker C. What we know about covid-19 reinfection so far BMJ 2021; 372 :n99 doi:10.1136/bmj.n99

Of 11 000 healthcare workers who had proved evidence of infection during the first wave of the pandemic in the UK between March and April 2020, none had symptomatic reinfection in the second wave of the virus between October and November 2020. As a result, the researchers felt confident that immunity to reinfection lasts at least six months in the case of the novel coronavirus, with further studies required to understand much more.

An early study by Public Health England, indicated that antibodies provide 83% protection against covid-19 reinfections over a five month period. Out of 6614 participants, 44 had “possible” or “probable” reinfections.

To date, most of the SARS-CoV-2 reinfections that have been reported have been milder than first encounters with the virus, although some have been more harmful—and two people have died as a result.

Boyton RJ, Altmann DM. Risk of SARS-CoV-2 reinfection after natural infection. Lancet. 2021 Mar 27;397(10280):1161-1163. doi: 10.1016/S0140-6736(21)00662-0. Epub 2021 Mar 17. PMID: 33743219; PMCID: PMC7969128.

The authors were able to determine that 3·27% of those who were uninfected during the first surge had a positive test during the second surge, compared with 0·65% among those who had previously recorded a positive test. Thus, they determined from that, in general, past infection confers 80·5% protection against reinfection, which decreases to 47·1% in those aged 65 years and older.

One of the largest datasets has come from Qatar during a period of high disease burden and reported an estimated reinfection risk of 0.2%.

Adnan I Qureshi, MD, William I Baskett, BS, Wei Huang, MA, Iryna Lobanova, MD, PhD, S Hasan Naqvi, MD, Chi-Ren Shyu, PhD, Re-infection with SARS-CoV-2 in Patients Undergoing Serial Laboratory Testing, Clinical Infectious Diseases, 2021;, ciab345, https://doi.org/10.1093/cid/ciab345

According to the results, reinfection occurred in 0.7% (95% CI, 0.15%-0.9%) of patients, with an average gap between positive tests of 116 ± 21 days. They found that asthma (OR = 1.9; 95% CI, 1.1-3.2) and nicotine dependence or tobacco use (OR = 2.7; 95% CI, 1.6-4.5) were associated with reinfection.