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The Statens Serum Institut (SSI) reported just 80 pertussis cases in Denmark in 2021, the lowest level the country has seen in many years.

Denmark/CIA

The decline occurred in contrast to the widespread pertussis epidemic in 2019 and early 2020 and is likely due to the COVID-19 pandemic.

n the spring of 2019, however, Denmark was hit by a long-running, nationwide pertussis epidemic that only stopped again when the government shut down the country due to the covid-19 epidemic on 11 March 2020.

During 2019, a total of 3,696 cases of pertussis were found – three to four times as many as you normally see in a whole year. The high numbers continued into 2020, when both historically high numbers of pertussis cases were reported in both January and February in 874 and 849 cases, respectively.

“During the previous pertussis epidemic in 2016, the highest number of cases found was 284 in one month. So the epidemic in 2019 and 2020 was unusually strong, ”says ward doctor Peter Henrik Andersen from SSI.

Nor was there any indication that the pertussis epidemic was dying out when Denmark was hit by the global coronavirus epidemic in February 2020.

In the week before March 11, when Prime Minister Mette Frederiksen closed the country and introduced extensive coronary restrictions, an average of 349 samples were taken daily to the laboratories for pertussis examination. This number dropped to just 26 samples on average per. day the week after the restrictions were introduced. Later, the number of samples has increased again, but the number of detected cases has remained very low.

“From the summer of 2020 and the rest of the year as well as throughout 2021, the number of pertussis cases was very low. It was an average of 6.7 cases per month, which is the lowest we have seen since the monitoring of whooping cough was introduced in its current form “, says Peter Henrik Andersen.

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He continues:

“The low number of cases is most likely due to coronavirus disease, which has had a positive effect on the number of respiratory infections in general. At the same time, the increased immunity in the population after the pertussis epidemic 2019-20 has probably put a damper on the infection with pertussis for some years to come. Just as we saw it after the minor pertussis epidemic in 2016. ”

122 children under two years affected

In 2020 and 2021, a total of 122 cases of pertussis were reported in children under two years of age.

Among these children, 31 children (26%) had not been vaccinated against pertussis, while 26 children (21%) had received all three pertussis vaccines.

According to SSI figures, the proportion of unvaccinated children under the age of two who became ill with whooping cough fell in 2020 and 2021, compared to 2018 and 2019.

“This may be due to the fact that in the autumn of 2019, an offer of free pertussis vaccination was introduced for pregnant women in the 2nd and 3rd trimesters. This gives the newborns better protection until they can receive their first vaccine at the age of 3 months, ”says Peter Henrik Andersen.

The offer of free pertussis vaccine for pregnant women has since been extended. That applies right now until the end of March 2022.

Out of the 122 pertussis children under the age of two, a total of 53 children (43%) were admitted for one or more days. However, the risk of hospitalization was highest among the youngest children under 6 months.