SARS-CoV-2 Transmission: Time to Rethink Public Health Strategy

SARS-CoV-2 transmission

As we enter the third year of the COVID-19 pandemic, many key questions about SARS-CoV-2 transmission dynamics remain unclear.

In The Lancet Infectious Diseases, Cheryl Cohen and colleagues explore the nuances involved in SARS-CoV-2 household transmission.

Current evidence supports transmission between household contacts as a substantial driver of SARS-CoV-2 spread.

Increased transmission in household settings is likely to be due to non-use of personal protective equipment and close prolonged contact during daily activities within the household.

Although evidence shows that people with asymptomatic COVID-19 can transmit SARS-CoV-2, the exact extent of this transmission was not known.

The prospective household cohort study of SARS-CoV-2, influenza, and respiratory syncytial virus community burden, transmission dynamics, and viral interaction in South Africa (PHIRST-C) by Cohen and colleagues comprehensively investigated the incidence, reinfection, and transmission dynamics within urban and rural households in South Africa.

Novel study methodology included intensive symptom screening, midturbinate nasal swabs twice a week for testing of SARS-CoV-2 with real-time RT-PCR (RT-rtPCR; irrespective of symptoms), and anti-SARS-CoV-2 antibody testing every 2 months. The study period coincided with three COVID-19 waves in South Africa, which were driven by original wild-type variant in the first wave, the beta variant in the second wave, and the delta variant in the third wave.

The study reports that 749 (62·4%) of 1200 participants were infected with SARS-CoV-2, based on RT-rtPCR and serology combined, and 87 (11·6%) of 749 were reinfected. The prevalence of asymptomatic infection was high (565 [85·3%] of 662 RT-rtPCR-confirmed episodes with available data), even in older participants (≥19 years; 220 [76·1%] of 289), when compared with a previous systematic review of 79 studies (1287 [19·5%] of 6616).

In contrast to existing evidence,

this study showed that household cumulative infection rate (transmissibility from the index case to susceptible household members) was similar between asymptomatic index cases (23·9% [175 of 731 susceptible household members infected]) and symptomatic index cases (23·3% [20 of 86]; odds ratio [OR] 1·0 [95% CI 0·5–2·0]). Increased household transmission was associated with the delta and beta variants (vs wild-type, OR 10·4 [4·1–26·7] and 3·3 [1·4–8·2], respectively) and increased SARS-CoV-2 viral load in the index case (OR 5·3 [2·3–12·4]).

Additionally, people living with HIV who had unsuppressed HIV viral loads (≥400 viral load copies per mL) were more likely to have symptomatic infection (OR 3·3 [1·3–8·4]), with longer shedding of SARS-CoV-2 (hazard ratio 0·4 [95% CI 0·3–0·6]), than HIV-uninfected individuals. This chronic persistent SARS-CoV-2 infection in patients with immunosuppression from uncontrolled HIV infection might promote the emergence of new variants.

Therefore, strengthening of antiretroviral treatment programmes is urgently needed, so that patients with advanced immunosuppression are prioritised for effective antiretroviral treatment and COVID-19 vaccination.

We think this study provides unique insights into the epidemiology of household transmission of SARS-CoV-2, in a largely unvaccinated population. The high prevalence of asymptomatic infection with similar transmission potential as symptomatic cases, and the need for frequent testing to detect transient infections, highlights the limitations and complexities of current screening and testing protocols. Symptom and temperature screening at entry points (eg, restaurants, schools, airports) might not have the public health infection containment benefit that was expected. Similarly, attempting to prevent nosocomial COVID-19 transmission by symptom and PCR screening on admission to hospital might miss transient infections if tests are not repeated regularly, given that patients with COVID-19 might not have symptoms, and transmission might have already occurred, despite a negative PCR test.

Current public health approaches encourage a combination of vaccination and non-pharmacological measures such as wearing a face mask, social distancing, hand sanitation, and ventilation strategies to prevent COVID-19 transmission.

This study suggests that the COVID waves in South Africa were potentially driven by household transmission in the young population, highlighting the difficulty in relying on non-pharmacological interventions as prevention and containment measures. At this time, vaccination remains the key public health intervention in high-risk populations that can provide immunity, and thus mitigate and limit severe infections, complications, and mortality from COVID-19.

HD reports personal fees from Merck Sharp & Dohme, Adcock Ingram, and conference attendance sponsorship from Merck Sharp & Dohme and Pfizer. AP declares no competing interests.
SARS-CoV-2 transmission
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