The ups and downs of immunization coverage

Several developed countries have achieved relatively high vaccine coverage. However, some of them see their number of deaths, hospitalizations and cases decrease more than others. There are many reasons for these disparities. Overview.

Alice Girard-Bossé
Press

The behavior of the population

The behavior of the population and governments is the most likely reason to explain the disparities between countries, believes Alain Lamarre, professor-researcher specializing in immunology and virology at the National Institute for Scientific Research (INRS). “In the Netherlands, Austria, Germany and Great Britain, the measures were released much faster than in Quebec after vaccination,” he gives as an example.

In countries like Spain and Portugal, extremely well vaccinated, or Italy, which has taken strong measures, the increase in the number of cases is not so striking, said epidemiologist Yves Coppieters, of the Free University of Brussels, at Agence France-Presse. The situation is however worrying in several European countries, in particular in Belgium. On the other hand, China is maintaining draconian containment measures in order to completely eliminate cases of COVID-19 on its territory, a strategy that Australia and New Zealand have abandoned.

Adherence to measures also plays a role, adds the D^D Maryse Guay, professor in the department of community health sciences at the University of Sherbrooke. “Populations who observe the measures well have less risk of contracting the virus and therefore of being hospitalized or of dying. Japan, for example, is recognized for its compliance with the wearing of masks and hand hygiene, ”illustrates the specialist.

The time between the two doses

Countries that have opted for a longer period between the two doses of vaccine would also be favored, say specialists. Indeed, vaccine efficacy against infections increases when the interval between doses is longer, demonstrated the National Institute of Public Health of Quebec (INSPQ). Quebec’s decision to allow an interval of 12 weeks between doses of the vaccine, so that more people can receive their first injection, has now been validated by scientific studies. “In Quebec, we postponed the second doses, because we did not have enough vaccines. In the end, our misfortune was our blessing ”, sums up the D^D Guay. Remember that a three-week delay was recommended for the Pfizer-BioNTech vaccine and four weeks for that of Moderna.

Access to healthcare

The reliability of the data is also questioned in some countries. “In India, where the health system is very unequal between the more rural and urban regions, it is estimated that there are perhaps twice or three times as many cases as what is recorded,” says Lamarre. To be able to correctly count the number of cases in a country, people need to be tested, so they need to have access to the tests, adds the D^D Guay. If some people do not have access to the health system, they cannot be hospitalized either. “Now we know how to better treat COVID cases than at the start of the pandemic, but some countries do not have access to all these treatments,” she said. In a country like India, they may not be able to keep a patient in intensive care for three months while they get better, says D^D Guay.

Population profile

Individual factors, the prevalence of which varies across populations, may also play a role, argues D^D Guay. “In the United States, for example, there is more obesity and more chronic diseases linked to obesity. When the disease sets in, people who are affected can more easily have complications and die from them, ”explains the specialist.

The moment

The timing of the start of the vaccination campaign may also have played a role, says Dr.^D Guay. The Delta variant, first identified in India, appeared in the spring, as several countries began their vaccination campaigns. “In Europe and England, the Delta variant began to circulate long before Quebec, which may have had an impact,” she says. Due to the decline in immunity over the months, some countries that had started vaccination very early, such as Israel, may have found themselves in a slightly more vulnerable situation, says Lamarre.