Covid-19 certification or 'vaccine passports' led to increased immunisation 20 days before and 40 days after introduction in countries with lower-than-average vaccination coverage, according to a modelling study published in The Lancet Public Health journal. Covid-19 certification requires people to have proof of complete vaccination, negative test, or disease recovery certificate, to access public venues and events.
It has been suggested that such certification might encourage more unvaccinated people to get vaccinated, particularly those who perceive their own risk of hospitalisation or death from Covid-19 as low. "As mass vaccination programmes continue to play a central role in protecting public health in this pandemic, increasing vaccine uptake is crucial both to protect the individuals immunised and break chains of infection in the community," said study lead author Melinda Mills, from the University of Oxford in the UK.
"Our study is an important first empirical assessment of whether Covid-19 certification can form part of this strategy," Mills said. The study linked data of Covid-19 certification introduced from April to September 2021 to vaccination uptake in six countries where certification was legally mandated: Denmark, Israel, Italy, France, Germany, Switzerland.
In countries where vaccine coverage was previously low, introduction of Covid-19 certification was associated with a significant increase in the number of additional vaccine doses per million people, the researchers said. This ranged from 127,823 in France, 243,151 in Israel, 64,952 in Switzerland and 66,382 in Italy, they said.
In contrast, in Denmark and Germany, where there were higher average vaccination rates before certification was introduced, there was no significant increase in vaccination, according to the study. The researchers noted that compared to the control countries, daily Covid-19 case numbers decreased after implementation in France, Germany, Italy, Switzerland, but increased in Israel and Denmark.
Many countries implemented certification as a response to rising cases, making it difficult to assess the effect of certification on reported infections, they said. The study authors said this highlights the importance of taking account of the phase of infection trajectory when the intervention is introduced.
After the introduction of Covid-19 certification, increases in vaccination were highest in people under 30 years old compared to older groups, the researchers said. They explored whether prioritisation of vaccine rollout among older age groups and eligibility in younger age groups around the time of certification may have influenced the results, but found that the effect could not be fully explained by age-based eligibility criteria.
In Switzerland, when Covid-19 certification was used to restrict access to nightclubs and large events only, increases in vaccination uptake was only observed in people aged under 20 years old, according to the study. When restrictions were expanded to include all hospitality and leisure settings, uptake also increased among those 20-49-year-olds, the researchers said.
The study suggests that the policy may be useful in encouraging uptake in particular groups, but more research investigating other factors, including socioeconomic status and ethnicity, is needed to fully understand who certificates could effectively target. "We know that certain groups have lower vaccine uptake than others and it may be that Covid-19 certification is a useful way to encourage vaccine complacent groups, like young people and men, to get vaccinated," said study co-author Tobias Ruttenauer from the University of Oxford.
"However, Covid-19 certification alone is not a silver bullet for improving vaccine uptake and must be used alongside other policies," Ruttenauer said. The researchers said vaccine hesitancy due to lack of trust in authorities may be addressed more successfully through other interventions, such as targeted vaccine drives and community dialogue to generate more understanding about Covid-19 vaccines.