Effectiveness of 2G and 3G has declined

At the request of the Dutch Ministry of Health, Welfare and Sport, researchers from TU Delft, UMC Utrecht and Populytics investigated the extent to which the various types of COVID certificates (coronatoegangsbewijs, CTB) can help to prevent the spread of COVID-19 in society. The 3G (vaccinated, recovered, tested) and 2G (vaccinated, recovered) rules are currently a lot less effective in curbing the spread of the virus than they were two months ago. A 1G policy (only people who have recently tested negative are given access) is much more effective. But, even if a 1G policy were to be introduced today, the reproduction number would not drop below 1.0.

The study
The Netherlands implemented a 3G policy in 2021: visitors to certain locations had to present a CTB to prove that they had recently tested negative, had recovered from coronavirus or were vaccinated. Other European countries opted for a 2G policy: only people who had recovered or were vaccinated were permitted to enter venues. A 1G policy has also been raised as an option in public debate. The aim of this study was to investigate the effectiveness of these types of the CTB in preventing the spread of the virus in society. The study comprised two modelling studies and a behavioural study. The modelling studies focused on: (1) the risk of individuals being infected and the number of hospital admissions among visitors to CTB venues and (2) the effect of the CTB policy on the spread of the virus in society (the reproduction number). The behavioural study was conducted among 3,079 Dutch citizens, 783 of whom were unvaccinated. The study was supported by a sounding board of experts from Erasmus MC, Erasmus University Rotterdam, TU Delft, UMC Utrecht and Radboud University.

Conclusions on the effectiveness of CTB policy
A CTB policy can reduce the number of infections and hospital admissions among visitors to CTB venues. The introduction of a 1G policy has a greater impact on reducing infections and hospitalisations among visitors than the introduction of a 2G or 3G policy. Although 2G and 3G policies do reduce the number of infections and hospitalisations among visitors to CTB venues, this effect has been greatly diminished by the arrival of the Omicron variant.

In November 2021, the 3G CTB policy helped to bring the reproduction number below 1.0. It was possible to curb the spread of the virus because the less infectious Delta variant was dominant at that time. In January 2022, however, introducing 2G and 3G CTB policies would not bring the reproduction number below 1.0 due to the higher infectivity of the Omicron variant.
The effect of 1G on the transmission of COVID-19 in society is less dependent on the level of population immunity than 2G or 3G. This would have a particularly significant effect if 1G applied to many locations (and therefore contact moments) and if tests used for entry were of a high quality.

The effect of 2G and 3G on the transmission of COVID-19 in society is strongly dependent on the level of population immunity. The 2G and 3G options are most effective when there is a large difference in the level of protection against infection between unvaccinated people who do not have a CTB on the one hand, and people who do have a CTB either through a vaccine or proof of recovery on the other. The study found that the effectiveness of 2G and 3G increases when the policy is used at more locations. 2G and 3G are more effective when a larger group of unvaccinated people have not yet had COVID-19. Potential fraud involving COVID certificates and the quality of testing have a much more limited impact on the effectiveness of 2G and 3G.

Omicron
The effect on limiting the spread of the virus in society through a CTB policy has been significantly reduced due to the emergence of the Omicron variant. One of the main explanations for the limited effectiveness of 2G and 3G is the declining protection offered by vaccination against infection with the Omicron variant. In an ideal situation, introducing 2G at all locations other than at schools and at home (e.g. work, restaurants and bars, supermarkets) in January 2022 could lead to a 16.0% reduction in the reproduction number; for 3G, this would be 15.3%. In an ideal situation, introducing 2G at all locations other than at schools, at home and at work in January 2022 could lead to a 9.8% reduction in the reproduction number; for 3G this would be 5.4%. The above figures are for the ideal situation, where we assume that the 2G and 3G CTB policies have a significant impact on the behaviour of unvaccinated people who do not have a long-term CTB. However, the behavioural study shows that a large group of unvaccinated people will opt for alternative activities with people other than their family members if they no longer have access to certain locations. By doing so, they will substitute contacts with a high risk of infection for other contacts with a high risk of infection, which means that 2G and 3G CTB policies will be less effective than in the ideal situation.

Implementing 1G would be much more effective. Introducing this policy at all locations other than at home, at schools and at work would lead to a maximum reduction in the reproduction number of 19.2%. In the most ideal situation, introducing 1G at all locations other than at schools and at home would lead to a 44.9% reduction in the reproduction number. However, even if 1G were to be introduced at all those locations, the reproduction number would still be higher than 1.0.

Conclusions from the behavioural study
A substantial group of Dutch people who have been vaccinated twice are unsure as to whether they should have the booster vaccination. This hesitancy is particularly pronounced among young people and among people who went for their first vaccines several months after receiving the invitation. The group of unvaccinated people who say they will get vaccinated if the CTB is abolished is larger than the group who say they will get vaccinated if the government introduces 2G or introduces 3G in several locations (work/education). We estimate that approximately 650,000 unvaccinated adult Dutch citizens visited locations requiring a CTB in November 2021. Between 300,000 and 325,000 people did so after testing negative for COVID-19. If this group no longer has access to these locations due to the introduction of 2G, around 40% will opt for alternative activities with people other than their family members. For example, they might choose to meet up at home rather than at a bar. The remaining 60% would not opt for alternative activities or would only opt for alternative activities with their family members.

More information
The full publication is available here (in Dutch).
Researcher: Niek Mouter, N.Mouter@tudelft.nl
Press office: Dimmy van Ruiten, D.M.vanRuiten@tudelft.nl, +31 15 2781588