COVID-19 infection rate was low among healthcare workers early in the pandemic

Results from a study in May 2020 of healthcare workers at the frontline of the battle against the COVID-19 pandemic in Saudi Arabia reveal that the seropositivity rate was low overall, though it varied across different regions and hospitals. 

Seroprevalence studies track the proportion of a population infected by a pathogen over a period of time. This is accomplished via immunoassays that measure the presence of antibodies in their blood serum. The prevalence of virus-neutralizing antibodies (NAbs) is an indicator of past infection as well as of immunity post-infection. 

The survey, the first of its kind in the kingdom, was conducted across 85 hospitals: 61 COVID-19 referral hospitals with confirmed COVID-19 patients, excluding those who were symptomatic, and 24 non-affected hospitals with no COVID-19 patients. The latter did not report any outbreaks among healthcare workers and were used as the control group. 

Blood serum samples tested from more than 12,600 healthcare workers had seropositivity rates from 0% to 6.31%. As expected, healthcare workers operating in case-hospitals with high COVID-19 exposure had a higher rate. In 8% of the tested samples, there was a lack of Nab due to the low level or presence of antibodies against coronaviruses. 

The low SARS-CoV-2 seropositivity could be an indication that vigilance in personal protective equipment and a nation-wide lockdown were successful in keeping the rate of asymptomatic COVID-19 in healthcare workers at low levels, says Naif Alharbi, study co-author, and head of the KAIMRC Vaccine Development Unit. 

 “This study is only part of the whole picture of COVID-19 epidemiology in KSA and needs to be taken in totality with other key studies and findings,” says co-author Jaffar A. Al-Tawfiq of Johns Hopkins Aramco Healthcare.

The seropositivity rate varied between regions and also with the number of community cases. “The variation in the seropositivity is likely to be related to the variability in the cases in that community or city.  Healthcare workers are part of any community and they could be exposed to SARS-CoV-2 in the community,” explains Al-Tawfiq.

Other studies have since been conducted to measure seroprevalence among the wider community in Saudi Arabia. Al-Tawfiq says that a study of blood from healthy donors found that the prevalence of antibodies to SARS-CoV-2 was low, although higher among non-citizens. Alharbi says that another survey showed that NAb is induced at a higher level in severe cases and peaks for three months post-infection. He has also been working on a more representative national seroprevalence study with over 11,000 samples collected between June and November 2020, which he hopes to publish soon.

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