Vaccination reduces risk of onward Covid-19 transmission, while reinfections are rare – ECDC technical review

People who have been vaccinated against Covid-19 pose a lower risk of passing the virus on, while those infected naturally can get sick again in rare cases, the EU's infectious disease agency said in a review of multiple studies.

The ECDC analyzed a plethora of international coronavirus studies in an attempt to understand the extent to which vaccination – or previous Covid-19 infection – hindered onward transmission of the virus from infected individuals to susceptible contacts. The agency shared their findings in a technical review released on Monday.

The review found evidence that “vaccination significantly reduces viral load and symptomatic/asymptomatic infections in vaccinated individuals, which could translate into reduced transmission.”

This means that the total number of Covid-19 cases, which so far stands at more than 120 million around the globe, is going to “decrease significantly” as more people are vaccinated in various countries, the agency, tasked with boosting EU defenses against infectious diseases, pointed out.

The ECDC found just a single study that specifically looked into the impact of vaccination on transmission of the virus. It was carried out in Scotland over the past year and suggested that vaccination of even one household member reduced the risk of infection in susceptible cohabitants by at least 30%.

As for those who contracted and recovered from Covid-19, the review noted that a previous infection didn’t provide “sterilizing immunity” from the disease. The protective effect remained at between 81% to 100% for five to seven months, and reinfection was a “rare event,” though still a possibility. “Some who are re-infected might still be able to transmit SARS-CoV-2 infection to susceptible contacts,” the review said.

The ECDC warned that new Covid-19 strains could still cause problems in the fight against the virus. It also pointed to the obvious lack of data on the duration of protection provided by vaccines, given how recently the first immunization drives kicked off.

Covid-19 has “the potential to escape human immune defenses induced by natural infection or vaccination,” and such cases have already been documented by scientists, it said, calling for more studies to better assess the transmission of the disease and ways to defend against it.

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