Researchers from TU Delft, UMC Utrecht and Populytics were commissioned by the Ministry of Health, Welfare and Sport to investigate the extent to which different variants of the corona access ticket can help prevent the spread of the corona virus in society. 3G and 2G policies are currently less effective in stopping virus spread than they were two months ago. A 1G policy (only recently negative tested people are allowed access) is much more effective. But even with 1G, the reproduction figure (R) cannot be brought below 1.0 at this time.

In the Netherlands, a 3G policy was applied in 2021: visitors to certain locations had to demonstrate through the corona access ticket (CAT) that they had recently been tested negative, cured or vaccinated. Other European countries opted for a 2G policy, where only people who were cured or vaccinated were allowed access. A 1G policy (which gives access only to recently negative tested people) was also mentioned in the public debate as an option. The purpose of this study was to investigate how effective these variants of the CAT are in stopping societal spread of the virus. The research consists of two model studies and a behavioral study. The modeling studies focused on: (1) individual infection risk and hospitalizations of visitors to CAT sites, and (2) the effect of CAT policies on the spread of the virus in society (R). The behavioral survey was conducted among 3,079 Dutch citizens, 783 of whom were unvaccinated. The study was overseen by a sounding board group with experts from Erasmus MC, Erasmus University Rotterdam, TU Delft, UMC Utrecht and Radboud University.

Effectiveness of CAT policies

A CAT policy can reduce the number of infections and hospitalizations among visitors to CAT sites. Implementing a 1G policy has a greater impact on reducing infections and hospitalizations among visitors than implementing a 2G or 3G policy. 2G and 3G lower the number of infections and hospitalizations among visitors to CAT sites, but this effect has become much lower with the entry of the Omikron variant.

In November 2021, 3G enabled the CAT to bring R below 1.0. The spread of the virus could be slowed because the less infectious Delta variant was dominant at that time. In January 2022, 2G or 3G will not allow the CAT to bring R below 1.0 due to the higher infectivity of the Omikron variant. The effect of 1G on the spread of the virus in society is less dependent on the degree of immunity of the population than 2G or 3G. The effect is especially large if 1G is applied to many locations (and thus contacts), and the quality of access testing is high.

The effect of 2G and 3G on virus spread in society greatly depends on the degree of immunity of the population. 2G and 3G are especially effective when there is a large difference in protection against infection between, on the one hand, the group of unvaccinated people who do not have a CAT and, on the other hand, the group who have received a CAT through a vaccine or a recovery certificate. The study shows that the effectiveness of 2G and 3G increases when the policy widely applied. The effectiveness of 2G and 3G is higher when the group of unvaccinated people who have not yet experienced COVID-19 is larger. Possible fraud with entry tickets and quality of testing has much less impact on the effectiveness of 2G and 3G.

The effect on limiting virus spread in society through a CAT has become much smaller with the entry of the Omikron variant. A major explanation for the limited effectiveness of 2G and 3G is the diminishing protection of vaccination against infection with the Omikron variant. In an optimal situation, the introduction of 2G in all locations other than school and home (think work, hospitality and supermarkets) can lead to a 16.0 percent reduction of R by January 2022, with 3G it is 15.3 percent. In the optimal situation, introducing 2G at all locations other than school, home and work can lead to a 9.8 percent reduction of R in January 2022 and at 3G it is 5.4 percent. These figures are about the optimal situation, assuming that the CAT has significant influence on the behavior of unvaccinated people who do not have a long-term CAT. However, behavioral research shows that a large group of unvaccinated people will choose alternative activities with people other than their family members if they no longer have access to certain locations. As a result, they substitute contacts with a high risk of infection for other contacts with a high risk of infection, which will reduce the effectiveness of 2G and 3G CAT compared to the optimal situation.

Implementing a 1G policy is much more effective. Introducing this policy at all locations other than home, school and work leads to a maximum reduction of R of 19.2 percent. In the most optimal situation, introducing 1G in all locations other than school and home leads to a 44.9 percent reduction of R. However, even if 1G is introduced in so many locations, the reproduction number remains higher than 1.0.

Behavioral research

A substantial group of Dutch people who have taken the first vaccines are unsure whether they will opt for the booster shot. The doubt is particularly high among young people and among people who only took the first vaccines a few months after they received an invitation. The group of unvaccinated people who say they will take a vaccine if corona access is abolished is larger than the group who say they will take a vaccine if the government introduces 2G or 3G in several places (work/education). We estimate that approximately 650,000 unvaccinated adult Dutch citizens visited locations requiring a CAT in November 2021. Between 300,000 and 325,000 did so after testing negative. If this group is no longer able to access these locations due to the introduction of 2G, about 40 percent will opt for alternative activities with people other than their family members. For example, they would meet at home instead of meeting at a café. The remaining 60 percent will not choose alternative activities or will only choose alternative activities with family members.