Friday, April 02, 2021

ECDC : Risk Of SARS-CoV-2 Transmission From Previously Infected or Vaccinated Individuals

 
United States COVID Vaccination Stats - Apr 1st - Credit CDC

#15,894


Later today I'll be gratefully going out to get my second (Moderna) COVID jab, and while there are still questions over how well it will protect against emerging and future variants, the evidence to date is that these mRNA vaccines are very safe and provide excellent (albeit not 100%) protection against serious COVID illness. 

Although the development and rollout of multiple safe and effective COVID vaccines has been a tremendous (and welcomed) accomplishment, these are first generation vaccines that are going up against a continually evolving SARS-CoV-2.   

No one should assume this to be a one-and-done vaccine volley against this virus.  Booster shots are already being developed, and it is too soon to let down our guard in public.  Even as the number of fully vaccinated individuals in the United States passes 56 million, we are seeing a fresh surge in cases.

Screenshot Johns Hopkins COVID Dashboard


Earlier this week the ECDC released a technical report on what we know about the risk of COVID transmission among those who have recovered from previous infection, or have been vaccinated.

While much of this data comes from before the rise of multiple new variants of concern (VOCs), the existing data is encouraging.

First the news report from the ECDC on these findings, followed by the executive summary and a link to the full report.
 

News story
29 Mar 2021
 
In the Technical Report 'Risk for SARS-CoV-2 transmission from newly infected individuals with documented previous infection or vaccination', published today, ECDC examines the evidence on the extent previous SARS-CoV-2 infection or COVID-19 vaccination prevents onward transmission from infected individuals to susceptible contacts.
“It is very encouraging to see that SARS-CoV-2 reinfections are quite rare. We also welcome the positive early indications that the risk of onward transmission seems to be reduced in those who are vaccinated. Although the effect of new variants of concern on transmission patterns needs to be closely monitored, we still expect that the total number of infections will significantly decrease as vaccination coverage increases” said Andrea Ammon, ECDC Director.
Concerning transmission from previously infected individuals, the following key points were concluded:
  • No studies directly measured SARS-CoV-2 transmission from reinfected individuals to their contacts. However, there was evidence showing that reinfections are rare. Studies that have followed people for 5 to 7 months after recovery from a SARS-CoV-2 infection have estimated that the protective effect of previous SARS-CoV-2 infection is very high (81% – 100%) during that period. It should be noted however, that many of these studies were carried out before the emergence of SARS-CoV-2 variants of concern and there is weak evidence that immunity induced against previously circulating SARS-CoV-2 strains may not have the same potency against variants of concern, in particular B.1.351 and P.1.

Among vaccinated individuals, ECDC’s review showed the following:
  • Evidence of the impact of vaccination on the risk of transmission is available from just one study, which suggests that vaccination of a household member reduces the risk of infection in susceptible household members by at least 30%.
  • There is evidence that vaccination significantly reduces symptomatic or asymptomatic infection in vaccinated individuals, although the vaccine efficacy varies by vaccine product and target group.
  • There is also some evidence of lower viral load and shorter duration of shedding in vaccinated individuals as compared to unvaccinated individuals, which could translate into reduced transmission.
  • Many of the studies on vaccine effectiveness were carried out before the emergence of SARS-CoV-2 variants of concern, and there is some evidence that vaccine efficacy could be decreased for some of the variants, in particular for B.1.351 and possibly also P.1.

Follow up of cohorts with previous SARS-CoV-2 infection and vaccination is needed to better assess the magnitude and duration of protection from reinfection and symptomatic disease, as well as the effect of protection against transmission.
The aim of this document is to provide a summary of the available scientific evidence on the risk of SARS-CoV-2 transmission to susceptible contacts from infected individuals with documented previous infection or vaccination.
Executive summary
More than one year into the SARS-CoV-2 pandemic, over 120 million people have been infected with the virus across more than 200 countries. Reinfections following natural infections with the same or a new SARSCoV-2 variant have been reported sporadically and questions remain concerning the duration of immunity following natural infection, and whether asymptomatic reinfected individuals may be able to transmit the virus.
COVID-19 vaccines have been evaluated for their efficacy and effectiveness against symptomatic COVID-19 infection and for reducing and/or preventing mild, moderate, or severe COVID-19 disease, including mortality. However, the vaccine trials have not been designed to measure reduction in transmission risk from infected vaccinated individuals to susceptible contacts.
In this context, it is important to understand the available scientific evidence on the extent to which previous SARS-CoV-2 infection or COVID-19 vaccination prevents onward transmission from infected individuals to susceptible contacts. Therefore, ECDC has conducted a review of published and pre-print literature on duration and characteristics of immunity following a natural SARS-CoV-2 infection due to any variant or after COVID-19 vaccination with any of the EU-authorised vaccines now available.
The review of evidence on natural immunity and possibilities for transmission from previously infected to susceptible contacts found that:
  • Evidence from studies specifically designed to assess the impact of previous infection on the risk of transmission is currently lacking. Infection with SARS-CoV-2 does not provide sterilising immunity for all individuals and some who are reinfected might still be able to transmit SARS-CoV-2 infection to susceptible contacts.
  • There is evidence that reinfection remains a rare event. Results from cohort studies confirm that the protective effect of previous SARS-CoV-2 infection ranges from 81% to 100% from Day 14 following initial infection, for a follow-up period of five to seven months. Protection against reinfection is lower in individuals aged 65 years and older.
  • These studies were carried out before the emergence of SARS-CoV-2 variants of concern (VOCs) and therefore there is limited preliminary evidence that immunity induced against previously circulating SARS-CoV-2 variants may not have the same potency or duration against the VOCs identified to date (in particular the B.1.351 and P.1 variants.)
  • As the number of individuals acquiring natural immunity increases, the total number of infections is expected to decrease significantly, leading to decreased transmission overall, unless the genetic changes in the circulating variants induce significant immune escape.
The review of evidence on immunity and possibilities for transmission from infected, previously-vaccinated individuals to susceptible contacts found that:
  • Direct evidence of the impact of vaccination on the risk of transmission is only available from one study, a large register-based household transmission study from Scotland. This study suggests that vaccination of a household member reduces the risk of infection in susceptible household members by at least 30%.
  • There is evidence that vaccination significantly reduces viral load and symptomatic/asymptomatic infections in vaccinated individuals, which could translate into reduced transmission, although the vaccine efficacy varies by vaccine product and target group. In light of this fact, the total number of infections is expected to decrease significantly as vaccination coverage increases, provided that there is a match between the vaccine strains and the circulating virus strains. This will lead to decreased transmission overall.
  • Follow-up periods for vaccinated persons are not yet sufficiently long enough to draw conclusions on the duration of protection against infection long-term. Antibody titres in vaccinated individuals peak at 3−4 weeks following vaccination.
  • Many of the vaccine efficacy studies were carried out before the emergence of SARS-CoV-2 VOCs. In studies that address the variants, there is limited preliminary evidence of reduced vaccine efficacy, in particular for B.1.351 and possibly also for P.1.
Follow-up of cohorts with previous SARS-CoV-2 infection and vaccination is needed to better assess the magnitude and duration of protection from reinfection leading to asymptomatic/symptomatic disease, and the effect of protection against further transmission to contacts.
As an RNA (ribonucleic acid) virus, SARS-CoV-2 will continue to evolve over time and its potential to escape human immune defences induced by natural infection or vaccination has already been documented. It is likely that in the future VOCs will continue to evolve and play a significant role in placing immunological pressure on the circulating viruses. It is not possible to predict when and where this will occur, however, cocirculation of the three VOCs (B.1.1.7, B.1.351 and P.1) has been noted in several EU/EEA countries.
Download
Posted by at